ALBERT

Beschreibung: The reliable determination of the total phosphorus (P) content stored in aquatic biota is essential for studies on nutrient stoichiometry, as well as for effective lake management measures. However, a variety of methods are found in the literature for sample P content determination, which renders it necessary to assess whether the data reported in different studies are comparable. We used different combinations of combustion durations, acid types and acid concentrations for sample digestion, and measured P concentrations subsequently with the standard colorimetric method. In addition, P contents of samples were assayed by ICP–OES and MP–AES methods. Our results confirmed that the variability among studies using different methods may explain some of the reported intraspecific and interspecific variation. We found that duration of combustion exerted the most important influence on the P retrieval, while acid type and acidity of the hydrolysing solution did not substantially influence the efficiency of sample digestion. We recommend using 8 h of combustion and 0.3 N HCl for acid hydrolysis prior to the colorimetric P analysis, and urge standardisation in the P analyses of biotic samples so as to obtain reliable results and data comparable among different studies.

Beschreibung: Reservoirs are intermediate ecosystems between rivers and lakes. These ecosystems break up the landscape by forming artificial lakes connected by rivers and change important ecological processes of lotic ecosystems (e.g. organic matter production and nutrient cycling) and thus have direct effects on aquatic biodiversity. We test the hypothesis that damming water courses exerts a negative effect on the zooplankton community by decreasing the alpha diversity. Samplings were conducted in 30 reservoirs and 29 natural lakes in the Neotropics, during two hydrological periods (dry and rainy) in 2001. The study analysed differences in alpha diversity, the number of rare, accessory and constant species, and species composition between the types of lakes. Alpha diversity was significantly higher in natural lakes and species composition differed between natural lakes and reservoirs. Zooplankton alpha diversity was positively related to total phosphorus (best model), indicating that productive environments (natural lakes) gather more species. Our results suggest that reservoirs have negative effect on community structure, whereas natural lakes have an important ecological function for biodiversity conservation because they are refuges for biodiversity.

Beschreibung: Copepods are major components of zooplankton in the Humboldt Current system. Here, intra-seasonal (monthly) variation of upwelling and its influence on the copepod community were assessed. Species abundances, species richness, diversity (Shannon–Wiener index) and dominance, were studied during four upwelling periods (2002–2009) at the Station 18 time series off of Concepción (36°S). Although 77 species were identified, most variability of the community structure was explained by few (〈10) species. A negative trend in copepod abundance over the years was associated with lower oxygenation of the mixed layer. A generalized linear model test for relationships among community descriptors and environmental parameters (temperature, dissolved oxygen, chlorophyll, and water column stratification) revealed that diversity was positively correlated with stratification. Upwelling variation, reflected in alternate periods (active and relaxed), characterized two distinct communities during the spring–summer. The study concludes that upwelling interacts with copepod populations by changing stratification, and temperature and oxygenation gradients. The study also suggests that greatly increased upwelling may negatively impact copepods by reducing oxygenation, cooling down the mixed layer and causing more advection. The same mechanisms may be operating in other systems, and thus this study provides clues on how zooplankton communities can respond to climate-induced variation of upwelling.

Beschreibung: Aquatic food webs are supported by primary production from within the system (autochthony) as well as organic matter produced outside of and transported into the system (allochthony). Zooplankton use allochthonous resources, especially in systems with high terrestrial loading and moderate to low internal primary production. We hypothesized that due to high terrestrial loads and remnant submerged terrestrial material, allochthonous resource use by zooplankton would be significant in all reservoirs and would decline along an increasing reservoir age gradient. Using hydrogen stable isotopes and a Bayesian mixing model, we estimated the contribution of allochthonous sources to organic matter pools and crustaceous zooplankton biomass for ten reservoirs. Dissolved organic matter (DOM) in all systems was dominated by allochthonous sources (posterior distribution median 〉92% allochthonous), while particulate organic matter (POM) composition varied (2–68% allochthonous) and had a lower allochthonous fraction in older reservoirs. There was no relationship between zooplankton allochthony and reservoir age. Crustaceous zooplankton allochthony varied among systems from 26 to 94%, and Chaoborus allochthony, measured in four reservoirs, was similarly variable (33–94%). Consumer allochthony was higher than POM allochthony in some reservoirs, potentially due to terrestrial DOM pathways being important and/or algal resources being inedible (e.g., cyanobacteria). As with many lakes, in the reservoirs we studied, allochthonous inputs account for a significant fraction of the organic matter of basal consumers.

Beschreibung: We investigated the seasonal influence of an effective size-selective planktivore, the anadromous alewife ( Alosa pseudoharengus Wilson), on summer zooplankton and phytoplankton communities in a series of lakes in Maine, USA (4 with and 4 without alewife) that ranged from oligotrophic to eutrophic to determine the role of lake trophic state in influencing the relative strength of top–down forces on phytoplankton biomass. Predation by young of the year alewife reduced the mean body length of cladoceran and copepod biomass from spring to summer in alewife lakes, while mean body length remained unchanged in nonalewife lakes. Cladoceran biomass decreased substantially from spring to summer in 3 of 4 alewife lakes, increasing only in the most eutrophic lake. Conversely, cladoceran biomass increased from spring to summer in 3 of 4 nonalewife lakes. Predation by alewife on zooplankton did not have consistent cascading effects on phytoplankton biomass. Analysis of planktonic biomass ratios (phytoplankton biomass: zooplankton biomass) suggests that cascading effects were stronger in oligotrophic systems and weakened with increasing trophic status, as ratios in alewife and nonalewife lakes converged at higher total phosphorous levels. Our results suggest that lake trophic status may influence the relative importance of top–down control of both zooplankton and phytoplankton biomass. The mechanisms that explain this pattern remain elusive and likely require additional efforts to estimate alewife densities, rates of zooplankton and phytoplankton production relative to consumption, and the influence of other physical lake features.

Beschreibung: The bullet tuna Auxis rochei , the little tunny Euthynnus alletteratus , and the Atlantic Chub mackerel Scomber colias are three small Scombridae with similar life-history traits such as overlapping epipelagic distribution and a shared spawning area in Tunisian waters. In this study, we compared the phylogeography and demographic histories of these species by analyzing the sequence variability of the mitochondrial DNA control region. None of the species showed genetic differentiation in their Tunisian distribution; however, we inferred three completely different population histories. E. alletteratus showed a demographic history of a very recent bottleneck followed by sudden population expansion probably consequence of a population decline in the Last Glacial Maximum. S. colias also presented a population expansion after collapse but in this case about ten-fold older than that observed in E. alletteratus . Finally, A. rochei presented a history of demographic stability. These contrasting population histories were discussed based on their possible differences in life-history traits, but the hypothesis of stochastic factors affecting the demography of these species was also invoked.

Beschreibung: Since the late 1980’s, a persistent green tide of floating Ulva without any clear seasonal fluctuation has occurred in Hiroshima Bay, Seto Inland Sea, Japan. We hypothesized that the persistence is due to the co-existence of Ulva species with different seasonal growth patterns, and monitored the seasonal composition and growth characteristics of the constituent Ulva within the green tide. Two morphological types of Ulva were identified, and one type, U. pertusa , was almost the sole constituent during winter and spring. The other type Ulva spp., which has marginal microscopic serrations on the thallus, was dominant during summer and autumn. Both Ulva showed the highest relative growth rate in early autumn, but growth of Ulva spp. was faster in summer than that of U. pertusa and inhibited in winter. U. pertusa had more eurythermal characteristics in which the growth rate remained relatively high in winter. Water temperature was the most correlated environmental variable for the seasonal growth of both Ulva types rather than light or nutrients, but more influential on Ulva spp. Recent increasing trend of ambient seawater temperature is considered to be favorable for the growth of both Ulva types and a causative factor of the green tide.

Beschreibung: Tadpoles reduce activity and increase hiding in the presence of dragonfly larvae. Several studies demonstrate that tadpoles showing this behaviour have slower growth, however, other studies have found no effect or even positive growth in tadpoles exposed to predators. A recent study demonstrated that swimming is an energetically expensive activity for Bufo arabicus tadpoles. Therefore, if food resources are abundant close to refuges, reduced activity may be an advantage and could offset the cost of reduced foraging. I tested this hypothesis by growing B. arabicus tadpoles with food provided either near or away from shelters, in the presence or absence of caged dragonfly larvae. In the presence of dragonfly larvae, tadpoles provided with food close to shelters were significantly larger than those with food further away. Control tadpoles under both food treatments were intermediate in size, although not statistically different from the predator + near food tadpoles. The results indicate that access to resources is the main determinant of growth in B. arabicus tadpoles and that the energetic cost of swimming is a secondary factor.

Beschreibung: Landlocked lagoons are naturally stressed environments. They are strongly influenced by freshwater input which not only varies naturally, but which is also impacted by anthropogenic activities. This study investigated the direct influence of freshwater discharges on the distribution patterns and abundance of benthic communities in two neighbouring landlocked coastal lagoons, assessing the whole system and the confluence area of each tributary. Sampling occurred in the wet and dry seasons of 2011 at two distances from freshwater discharge locations. Both lagoons were colonized by species from two different pools, freshwater and marine. Freshwater flow rates had a direct influence on the spatial structure of the benthic communities of brackish-water/freshwater interface areas, where also specific taxa can act as early indicators of freshwater input variations. The intensity of this influence is highly dependent on lagoon size, creating spatial heterogeneity or affecting the entire system. The benthic fauna at the confluence of the tributary that depends almost exclusively on groundwater showed the lowest variability, suggesting that the biogeochemical nature of the groundwater may be a central cause for setting specific ecotones. The results suggest that benthic communities of landlocked coastal lagoons can be highly impacted by flow reduction from freshwater aquifers under drought conditions or water abstraction activities.

Beschreibung: We examined the settlement preferences of leeches by analysing colonization patterns on artificial substrates. The intention was to check whether the type of material, texture and size of artificial substrates would influence the abundance of leeches. To test substrate type preferences, we used the following nine artificial substrates: polyester, polycarbonate, aluminium, glass, rubber, steel, polyethylene, ceramics and polypropylene. In addition, substrates of different textures (structural vs. smooth) and sizes (900, 400, 100 cm 2 ) were used. We found that rubber, polyethylene and aluminium were most frequently chosen by the leeches. Surface structure and size of the objects were other factors which determined substrate selection by these organisms. Leeches more readily inhabited rough surfaces and the surfaces of smaller-sized objects. The species composition of leech assemblages on analysed artificial substrates was dominated by predatory taxa of the genus Erpobdella and Helobdella .

Beschreibung: The use of multiple taxa rather than a single taxon of stream organisms in ecological studies appears to be necessary to interpret independent environmental influences and interactions. We tested if macroinvertebrate assemblages in Indiana, USA, streams were better predicted from co-occurring fish assemblages or environmental variables. We used multivariate analyses to identify significant environmental predictor variables for macroinvertebrate and fish assemblages. Macroinvertebrate distribution and relative abundance were best predicted by in-stream cover and turbidity, and fish distribution and relative abundance were best predicted by fine sediments, bedrock, water temperature, and pool habitat. Patterns in fish assemblages were not significant predictors of macroinvertebrate distribution and relative abundance. Mantel tests for covariation among fish assemblage composition and macroinvertebrate assemblage composition resulted in significant, but low correlations. Our results suggest that macroinvertebrates respond to local environmental variation, and less to local presence of fishes indicating the surrogate taxa approach has little use at the Eastern Cornbelt Plain ecoregion of Indiana. Stream surveys of multiple taxa and environmental variables are appropriate assessment methods for ecosystem integrity.

Beschreibung: Bluemouth, Helicolenus dactylopterus is zygoparous species with internal fertilization spawning multiple batches of early-celled embryos in gelatinous masses. Its unusual reproductive strategy required methodological adjustments to estimate potential annual fecundity. The present study applied an adaptation of the gravimetric method, estimated batch fecundity based on different spawning fraction criteria (gestation, early-celled, and blastula females), and compared these estimates with the number of developing oocytes (NDOR) in the beginning of spawning to clarify the oocyte development pattern. Spawning fraction estimation based on the gestation criterion was considered the most reliable given its low variance and the subjectivity of staging early-celled embryos. On average, 87 batches were spawned with a mean spawning interval estimated at 1.73 days, and a mean relative annual total fecundity of 1,773 embryos g −1 carcass. The inexistence of a clear decreasing trend in the NDOR throughout the spawning season, and the lower NDOR estimates in females in the beginning of spawning comparing with relative annual fecundity (gestation criterion) suggests vitellogenic oocyte recruitment supporting previous results of indeterminate fecundity in Portuguese coast. The method proposed can be considered in fecundity studies of other commercial important species which extrudes gelatinous egg masses.

Beschreibung: In recent years, it has been recognized that the laser diffraction gives valuable information on particle size distribution for all types of dry inorganic or even organic materials. With use of the laser diffraction and the laser granulometer, this paper presents the changes occurring in the granulometric distribution of algal agglomerates and the changes in values of percentiles 10, 50 and 90%, determined basing on volume distribution. While assessing the granulometric composition, the existence of a proportional relationship between the diameter values corresponding to the percentile of 10, 50 and 90% was observed. What is more, the obtained results give insight into the possibility of application of the general Avrami equation to describe the granulometric composition of the algal suspension through the analogy of crystals formation from saturated solutions. The analysis shows that the model described by the modified Avrami equation adequately matched the regression to the experimental data on the granulometric composition of algal suspensions. The values of the correlation coefficients were close to 1, which proves that the regression model explained nearly all cases by the dependent variable V i  =  F ( d i ).

Beschreibung: The morphological and genetic structure of Western Mediterranean trout Salmo cettii inhabiting basins in Sardinia was completed to assist the design of its conservation programmes. Genetic analysis of protein-coding LDH-C1 plus sequencing mitochondrial control region gene and analyses of morphological characters described 253 specimens from seven localities in two basins in Southwest Sardinia. Nuclear and mitochondrial analyses revealed all of the fish were pure-bred native S. cettii , with no introgression from allochthonous S. trutta . The novel 18 mtDNA control region haplotypes were clustered in an ‘insular’ clade, strictly related to the Adriatic haplogroup, and depicted a radial network around two ancestral haplotypes. Completion of discriminant analysis using data on body pigmentation and quantitative morphologic parameters revealed three phenotypic groups within the fish. Each population and phenotype, characterised by high values of nucleotide and haplotype diversity, were not genetically differentiated and not geographically structured according to the two hydrological basins. Geometric morphometric analysis, based on 15 landmarkers, revealed pronounced and highly significant differences in body shape morphology between populations, suggesting S. cettii is locally adapting to extreme environmental conditions and so future management plans for these populations should treat the two basins as distinct morphological units.

Beschreibung: The dynamics of fluorescent organic matter (FOM) in lakes have generally been studied over extended periods of weeks to months rather than short time scales. We employed spectrofluorometry to examine whether short-term in situ variations in the three components of FOM (protein-like, terrestrial, and marine fluorescence) were related to changes in production in Lake Kinneret, Israel. Protein-like fluorescence correlated strongly with phytoplankton biomass, chlorophyll a, and Secchi depth in situ, suggesting it might serve as an indicator of aquatic production. In vitro dark incubations of filtered and unfiltered surface lake water (without added nutrients or organic matter) revealed considerable protein-like and marine fluorescence production in the unfiltered samples, suggesting that FOM is linked to particulate matter dynamics and to microbial processing of this suspended material. Terrestrial fluorescence did not significantly change in incubation, indicating that this component is probably produced deeper in the lake. Moreover, the lack of marine FOM accumulation in surface waters, despite producing in vitro, suggests that FOM photobleaching may regulate this component.

Beschreibung: The harmful bloom-forming cyanobacterium Cylindrospermopsis raciborskii grows in freshwaters over a wide range of light conditions. This species has increased its global distribution recently. The influence of ultraviolet radiation (UVR) on the fitness and toxin production of C. raciborskii has not previously been explored. We performed short-term experiments with three C. raciborskii strains (MVCC19, LB2897, and CYP011 K), and we compared their responses with other bloom-forming species ( Microcystis sp.1 and Plankthotrix agardhii ) to determine the impact of UV-B radiation on pigments, biomass, and morphological traits. In addition, we analyzed the effect of UV-B on the saxitoxin content and sxtU gene expression in the strain MVCC19. C. raciborskii strains were stressed differentially by UV-B exposure as evidenced by changes in growth, morphology, and heterocytes number. A significant increase in saxitoxin concentration and sxtU gene expression under UV-B suggests that toxin production in C. raciborskii can be a response to UV-B stress. In comparison, Microcystis sp.1 was more tolerant, while P. agardhii was severely impacted by UV-B, indicating also different sensitivities among cyanobacteria to UVR. Our results underscore the influence of UVR on C. raciborskii and the differences between strains which showed phenotypic plasticity, which potentially could affect its distribution in freshwaters.

Beschreibung: Predatory control of community structure, through consumption of herbivores and subsequent positive effects on the biomass or productivity of primary producers is common in marine ecosystems. We designed an experiment to analyse the effect of large-sized predators on the development of the macrofouling assemblage of a harbour. Predation was manipulated by randomly assigning artificial substrata to three treatments: (1) exclosure cages preventing access of large predators, (2) cage controls, i.e. cages with lateral walls but without roofs, allowing predators free access, (3) uncovered panels. Substrata were submersed horizontally and upper surfaces sampled at quarterly intervals over a 1-year period. No differences in species richness were observed among treatments but diversity was lower within exclosure cages than on cage controls/uncovered panels. In sessile assemblages, structure differed between treatments: cage controls/uncovered panels were dominated by algae and associated mesoherbivores, which were scarce/absent within cages. Exposure to predators also affected the structure of mobile assemblages. The sea urchin Pseudechinus magellanicus (Philippi) occurred within exclosure cages but was never found on exposed panels. We conclude that large predators exert a significant effect on assemblage structure and diversity, indirectly promoting the development of filamentous algae and mesoherbivores by controlling the abundance of browsers.

Beschreibung: To investigate whether dinoflagellates and diatoms interact with the polyp stage of Aurelia sp., feeding responses to dinoflagellates and diatoms and the survival of polyps fed on phytoplankton or Artemia sp. were studied in laboratory experiments. Feeding responses to motionless diatoms, defined by the movement of the polyp tentacles, were seldom seen but responses to motile dinoflagellates were clearly observed. Meanwhile, the feeding response was significantly positively related to the equivalent spherical diameters of the dinoflagellates. Gastric cavity analysis indicated that micro-phytoplankton ( Alexandrium catenella, Akashiwo sanguinea), which were in high concentration, could be detected, but nano-phytoplankton ( Prorocentrum donghaiense , Karenia brevis ) were not detected, implying that nano-phytoplankton were not eaten by Aurelia sp. polyps. We also observed that dinoflagellates whether nano or micro lost their motility and became attached on Aurelia sp. polyps. Compared to feeding on Artemia sp. nauplii, survival of the polyps was significantly depressed after 91 days feeding on phytoplankton in all combinations of species and concentrations. High mortality of the polyps when feeding on a high concentration (80 mg C l −1 ) of dinoflagellates implied that the polyps may be harmed when they coexisted with dinoflagellate blooms, so that the mass occurrence of large numbers of Aurelia medusae in natural coastal waters was depressed.

Beschreibung: Blooms of Nemopilema nomurai medusae have plagued East Asian coastal waters during the last decade. Recent studies indicate that the benthic polyp phase is important for reproductive potential and survival in scyphozoans. We investigated the effects of temperature and food on the development of N. nomurai polyps in the laboratory in Dalian, China. First, polyps were exposed to temperatures of 2.5–27.5°C in 2.5°C intervals. Next, we assessed the long-term cold tolerance by subjecting polyps to 0°C for 90 days. Third, we tested polyps in 16 combinations of temperature (8, 12, 16, and 20°C) and food supply (0.42, 1.25, 2.08, and 2.91 μg C polyp −1  day −1 ). Our results showed that N. nomurai polyps can survive from 0 to 27.5°C and overwinter without feeding. Production and excystment of podocysts did not occur at temperatures below 10°C. Somatic growth, podocyst-formation, and excystment increased with increasing temperature and were dramatically affected by food supply at warmer temperatures. Thus, warm temperatures (15–27.5°C) and abundant plankton biomass during the previous season should result in high productivity of polyps and significantly contribute to blooms of N. nomurai the following year.

Beschreibung: The rationale, the design, and the methods that have been used in the Chinese National Basic Research Project on “Giant Jellyfish Blooms in Chinese Seas” are described. Sixteen papers resulting from the project are published in the present special issue, and these are individually addressed.

Beschreibung: Aurelia spp. are among the main blooming jellyfish species. The polyp stage plays an important role in its outbreaks. To determine how temperature and food conditions may affect the process of reproduction, we maintained Aurelia sp. 1 polyps in the laboratory at three temperatures (10–15°C) and four food concentrations (0–0.1 mg C l −1 ) to test their combined effects on the strobilation process and the production of buds and ephyrae. The length of the strobilation preparation period significantly decreased with increased temperature, but was not affected by food conditions. With sufficient food supply, the polyps that had already released ephyrae restart the strobilation process. Food condition positively affects both the production of buds and ephyrae. Temperature, however, had different effects: at the three temperatures tested, 13°C was most appropriate for polyps to release ephyrae, while bud production was highest at 15°C. These results suggest that eutrophication (as a proxy for food condition) would affect both the size of the Aurelia sp. 1 polyp population and juvenile medusa population, whereas temperature adjusts the reproductive energy distribution between budding and ephyra release to regulate the strobilation process. This temperature adjustment mechanism likely helps match the production of juvenile medusae with the peak of zooplankton biomass.

Beschreibung: Frequent blooms of the giant jellyfish, Nemopilema nomurai , have occurred in the East Asian Marginal Seas since 2000 and have had a devastating effect on commercial fisheries. To determine the probability of future bloom development to permit effective countermeasures, it is essential to assess the influence of environmental factors on polyp development. In this study, the effects of salinity on the polyps of N. nomurai from the coastal waters of Dalian in the northern Yellow Sea were tested at salinities ranging from 2.5 to 45. The combined effects of salinity (15 and 32) and light intensity (800, 400, and 0 lux) in a 12-h light–12-h dark photoperiod were also assessed. The lower and upper salinity limits for N. nomurai polyp survival were 10 and 40, respectively. The salinity range of 20–27.5 was best for podocyst reproduction. Survival and somatic growth of polyps, and their asexual production of podocysts, were significantly greater at low to middle than at high salinities. Polyps survived, grew, and produced podocysts at all light intensities tested; however, differences in light intensity induced few statistically significant changes. These results indicated that N. nomurai polyps are adapted to survive, grow, and reproduce in estuaries and near-shore environments.

Beschreibung: Environmental factors such as temperature and food type affect the rate of asexual reproduction of jellyfish at the polyp stage. Combinations of three temperatures (10, 15, and 20°C) and four food treatments ( Prorocentrum donghaiense , Skeletonema costatum , Artemia sp. nauplii, and no food) were established to examine the asexual reproduction strategy of Aurelia sp.1. The results allowed us to reject two null hypotheses: no effect of temperature and no effect of food. A change from 20 to 15 or 10°C induced polyps to release ephyrae when food was present, while polyps without food did not strobilate. Polyps with Artemia sp. nauplii as prey produced more polyps through buds and podocysts, as well as more ephyrae through strobilation. At 20°C, the mortality rates of polyps exceeded 50%, except for those served by Artemia sp. nauplii. The number of polyps increased rapidly with Artemia sp. nauplii as prey. We conclude that when animal prey is limited, plants can serve as a nutrient source and satisfy the energy requirements for polyps at lower temperatures (10 or 15°C). Phytoplankton cannot provide adequate nutrition to polyps at higher temperature (20°). Abundant animal prey and suitable temperatures are essential conditions for polyps to strobilate and release ephyrae, leading to jellyfish blooms.

Beschreibung: The scyphozoan Aurelia aurita (Linnaeus) s. l., is a cosmopolitan species-complex which blooms seasonally in a variety of coastal and shelf sea environments around the world. We hypothesized that ephyrae of Aurelia sp.1 are released from the inner part of the Jiaozhou Bay, China when water temperature is below 15°C in late autumn and winter. The seasonal occurrence, growth, and variation of the scyphomedusa Aurelia sp.1 were investigated in Jiaozhou Bay from January 2011 to December 2011. Ephyrae occurred from May through June with a peak abundance of 2.38 ± 0.56 ind/m 3 in May, while the temperature during this period ranged from 12 to 18°C. The distribution of ephyrae was mainly restricted to the coastal area of the bay, and the abundance was higher in the dock of the bay than at the other inner bay stations. Young medusae derived from ephyrae with a median diameter of 9.74 ± 1.7 mm were present from May 22. Growth was rapid from May 22 to July 2 with a maximum daily growth rate of 39%. Median diameter of the medusae was 161.80 ± 18.39 mm at the beginning of July. In August, a high proportion of deteriorated specimens was observed and the median diameter decreased. The highest average abundance is 0.62 ± 1.06 ind/km 2 in Jiaozhou Bay in August. The abundance of Aurelia sp.1 medusae was low from September and then decreased to zero. It is concluded that water temperature is the main driver regulating the life cycle of Aurelia sp.1 in Jiaozhou Bay.

Beschreibung: The Scyphozon Cyanea nozakii is a common jellyfish species that blooms in Chinese seas. However, little is known of the field ecology of this species for the lack of polyps. Here, we studied a breeding technology of C. nozakii that included artificial acclimation of wild jellyfish, stimulation of spawning, as well as polyp and medusa rearing. Female and male medusae were observed to have dark brown ovaries and milky white testes, respectively. Massive spawning was stimulated by continuous light (1,000–1,500 lux) about 4 h a day. Planulae of C. nozakii were used as initial feed for rearing four-tentacle polyps. This food was replaced by Artemia nauplii when polyps developed to intermediate and fully developed stages. Ephyrae and 50 mm medusae were also obtained under laboratory conditions, though the survival rates of both stages were only about 20%. In this paper, we described a process of large-scale breeding of C. nozakii polyps, and finally making about 600 pieces of 30 × 40 cm 2 corrugated plates adhered with four polyps per cm 2 .

Beschreibung: Blooms of the scyphozoan jellyfish Aurelia spp. are directly affected by the number, survival, and ontogenetic process of the ephyra stage. To determine the combined effect of temperature and food conditions on the production of ephyrae, the rising- and decreasing-temperature experiment was designed to simulate the warming from spring to summer and the cooling from fall to winter, respectively. Results showed that both temperature and prey concentrations significantly affected the ephyra production. Aurelia sp. 1 strobilation occurred from 8 to 17°C, while 13°C was the optimal temperature for ephyra production. At 8, 10, and 17°C, when the parental polyps had abundant food, the released ephyrae had a larger bell diameter and a better nutritional foundation. Abundant food conditions in the field would therefore elevate ephyrae survival rate, accelerate individual development, and thus ensure the population size of medusae. Our results indicate that a longer spring and a relatively higher zooplankton biomass may increase blooms of Aurelia sp. 1. However, the limited food conditions present in autumn and winter most likely mean that the Aurelia sp. 1 ephyrae released during these seasons are not the main source of the following year’s medusa population.

Beschreibung: In East Asian waters, concern about giant jellyfish blooms, including Nemopilema nomurai (Cnidaria: Scyphozoa: Rhizostomeae), has increased in recent decades. Based on surveys in 2012 and 2013, as a part of the Chinese Jellyfish 973 Program, we investigated the life cycle in situ of the planktonic stages of this species in the Yellow Sea and the East China Sea. We found the following results: (1) Offshore of the Changjiang River is one of its principal breeding places, and is the area where the pelagic stages of N. nomurai appear earliest in the YS and ECS. (2) The general distribution pattern of pelagic stages of N. nomurai described previously in the YS and ECS is confirmed from the 2012 and 2013 surveys: From this small area (31.50–33.00°N, 122.00–122.75°E) usually in late May and early June, it expanded into the 31.5–36°N sea area (aggregating in 32–34°N) in June, then continued to expand northward and southward to 30–37°N by August, and then shrank to 34–37°N in October. (3) The biomass and abundance of N. nomurai in 2012 both in June and August were higher than those in 2013. (4) We confirmed that almost all pelagic stages of N. nomurai in the YS and ECS were confined north of 30°N. The breeding places, population dynamics, and mechanism of formation of the distribution pattern of N. nomurai in the YS and ECS in recent years are presented.

Beschreibung: This study evaluates the size-dependent predation of fish larvae by jellyfish, exemplified with flounder Paralichthys olivaceus and moon jellyfish Aurelia aurita under laboratory conditions. The effects of some environmental factors on the size-dependent predation were also investigated. The results indicate that the predation rate increased with larval development, until the larvae had developed the ability to actively avoid predation at approximately 11-day post-hatching and decreased thereafter. This suggests a size-dependent predation on the fish larvae. Water temperature and predator size significantly affected the predation rate of the medusae on the fish larvae, but the temperature and size effects were markedly reduced as the larvae reached post-larval stage. These findings suggest that water temperature and jellyfish size interacted with the ontogenetic development of the fish larvae to affect the predation rates. The presence of alternative prey Artemia salina , could alleviate the predation rate on the fish larvae, whereas light conditions showed no effects on the predation rate. Due to their overlaps in spatial and temporal distributions along the north Chinese coast, jellyfish are likely to prey upon flounder larvae and thus affect the recruitment of the wild fish populations.

Beschreibung: The biotic resistance hypothesis provides one of several explanations for the limited biological recovery of streams recovering chemically from acidification. The hypothesis proposes that acidification has changed the presence, abundance and interactions among species in acidified streams to the extent that acid-sensitive colonists cannot re-invade even where acidity has ameliorated. As a first step in testing for biotic resistance in streams, we conducted a field experiment to determine whether the success (growth rate) of acid-sensitive recolonists (mayfly nymphs, Baetis rhodani ) is reduced by competition with abundant acid-tolerant residents (stonefly nymphs, Leuctra inermis ) in a chemically recovering Welsh stream (UK). Gut contents analysis revealed a marked overlap in resource use between the two species. However, when Baetis was exposed to several (0, 0.25, 0.5 and 1 times ambient) densities of its putative competitor, Leuctra , growth rates of the colonist were not affected by the residents at any of the densities tested. These results do not support the hypothesis that resident species constrain colonist populations by affecting growth rates through competition for limited resources or interference. Further work is required to assess whether independent and/or interactive ecological effects of other common residents might affect colonists in ecosystems recovering from past stressors.

Beschreibung: The round goby Neogobius melanostomus has successfully invaded much of the Baltic Sea. However, very little is known about the feeding habits of the species in this newly invaded environment. Our laboratory experiment showed that the round goby is able to effectively consume a diverse variety of prey when given the choice between dominant benthic invertebrates: bivalves ( Macoma balthica , Mytilus trossulus , Cerastoderma glaucum ) and amphipods ( Gammarus spp.). In contrast consumption of the gastropod ( Theodoxus fluviatilis ) was very low in all provided combinations. Nevertheless, the round goby had no statistically significant preference towards any of the prey taxa. The round goby exhibited size-specific consumption of M. trossulus , with smaller individuals being consumed at least 25% more than larger size classes. In addition elevated prey density resulted in higher consumption of prey by the fish. The broad diet suggests that shifting densities of benthic invertebrate prey has little influence on the further dispersal of the round goby in the Baltic Sea as the species is potentially able to switch between several native invertebrate taxa. This opportunistic feeding behaviour has likely favoured this invasion and ensured success of the species in the invaded ecosystem.

Beschreibung: Clonal plants benefit from the ability to translocate resources among interconnected ramets through clonal integration to colonise ubiquitous heterogeneous habitats, which may contribute to the invasiveness of exotic clonal plants. To test this hypothesis, a greenhouse experiment was conducted to investigate the effects of clonal integration on a non-native clonal plant, Myriophyllum aquaticum , subjected to spatial and temporal heterogeneity of water supply. The daughter ramets were grown with stolon connections either severed from or connected to the mother plant and subjected to different amounts or frequencies of water supply. Clonal integration significantly improved growth and photosynthetic performance of daughter ramets that were exposed to spatial and temporal heterogeneity of water supply. Biomass allocation to roots of offspring ramets changed with water supply to enhance the capacity for water uptake. The decrease of the maximum quantum yield of photosystem II ( F v / F m ) as a function of reduced water supply was greatly alleviated by stolon connection. Moreover, clonal integration facilitated stabilisation of foliar N concentration and C/N ratio to support healthy growth of the ramets. These results suggest that clonal integration may facilitate invasion of M. aquaticum when subjected to heterogeneity in resource supply under ever-changing environments.

Beschreibung: Streams receiving agricultural runoff are typically enriched with nutrients, which variously impact stream communities. We examined the effects of phosphate and nitrate enrichment on leaf litter breakdown, microbial biomass and the nutrition of an invertebrate shredder to determine how nutrients are transferred through the stream detrital food web. Using artificial streams, individuals of Anisocentropus kirramus (Trichoptera: Calamoceratidae) were fed leaves of Apodytes brachystylus (Icacinaceae) under different nutrient regimes. We measured the amount of leaf material consumed or decomposed and the microbial biomass colonising the leaves. The dry mass, and protein, lipid and carbohydrate composition of A. kirramus larvae were determined after 28-day feeding on the leaves. Supplements of phosphorus, but not nitrogen, enhanced leaf breakdown, microbial growth and growth of larvae. Microbial biomass and dry mass of larvae increased with nutrient enrichment and they were significantly correlated. Thus, the phosphorus supplement was transmitted through the detrital food web via the microbial pathway, resulting in higher nutritional quality of leaves and enhanced physiological condition of the shredder. Understanding such subtle relationships is important in determining the impacts of anthropogenic contaminants on freshwater ecosystems.

Beschreibung: Assessing ammonium (NH 4 + ) availability in aquatic systems requires accurate concentration and turnover rate data. Water column NH 4 + regeneration, potential NH 4 + uptake, and nitrogen (N) fixation rates were measured in Missisquoi Bay, Lake Champlain, to help constrain internal N dynamics affecting phytoplankton community structure and cyanobacteria (Cy) blooms. Cyanobacteria dominated phytoplankton biomass during occasional summer bloom periods, but low or undetectable N 2 fixation rates and low heterocyte abundances suggested that N fixing cyanobacteria did not rely on atmospheric N 2 . Light/dark incubations revealed that photosynthetic and dark NH 4 + uptake generally were balanced, highlighting the importance of bacterial uptake. Our results suggest that phytoplankton were not controlled by nutrients from the “bottom-up”; rather, water column N dynamics responded to phytoplankton patterns. Basin-scale water column NH 4 + regeneration rates were about 700,000 mol N day −1 (9.8 t N day −1 ), which is almost twice the estimated N load from tributaries, and suggests a primary role for water column N regeneration in supporting primary production. Comparisons of basin-scale NH 4 + regeneration and demand imply that primary production is not sustained fully by combined water column regeneration and tributary N inputs; thus, future research should constrain additional sources and sinks affecting N balance in this and other aquatic systems.

Beschreibung: The reconstructed Lake Karla, Greece, has been undergoing its water-filling period since November 2009. In this paper, we aimed at investigating whether the unicellular eukaryotes, including the toxic/parasitic ones, that have been found during mass fish kills in the lake (March–April 2010), persist during the first warm period of the lake (May, August, November 2010). Given that microscopic characterization of some of these eukaryotes is not adequate for their identification, we analysed the 18S rRNA gene diversity of plankton samples. All the found phylotypes belonged to the phyla of Mesomycetazoa, Chlorophyta, Fungi, Alveolata, Cercozoa, Cryptophyta and Stramenopiles. Some members of these groups seem to persist in Lake Karla as they have been found in early spring as well. These microscopic eukaryotes are either ichthyotoxic/parasitic (e.g. Pfiesteria sp./ Pseudopfiesteria shumwayae , some Fungi, Mesomycetazoa, Lagenidium sp., Cercozoa) or indicative of hyper-eutrophic conditions (e.g. Oocystis sp., Scenedesmus spp.) and were rather abundant during the first spring–autumn period of the lake’s refilling process. These complex microscopic communities are expected to shape highly dynamic and variable food webs with the risk of repeated fish kills.

Beschreibung: Subfossil chironomid and sediment geochemistry data from Lugu Lake, a large high-elevation lake in southwest China, were used to assess the influences of climate warming and direct human impacts on the lake through time. A 95-year-long sediment record was recovered from the lake. Principal components analysis (PCA) and redundancy analysis of fossil chironomid data were performed to determine the controlling factors on the chironomid community. The four prominent environmental controls were summer air temperature, organic matter C:N ratio (C org :N), dry mass accumulation rate (DMAR), and total nitrogen. C org :N proved to be the most important controlling factor through time. However, C org :N and summer air temperature were highly co-linear, possibly due to temperature directly impacting lake productivity (and thus C:N ratios) through increased stratification and a longer growing season. PCA Axis 1 scores were a strong predictor of summer temperatures even after DMAR was factored out to account for direct human influences. The strong temperature–chironomid relationship over the last 50 years could be due to the lake becoming more responsive to climate warming after cultural eutrophication of the 1950s, as lakes with higher nutrient loads are shown to be more responsive to the effects of climate warming.

Beschreibung: The impacts of climate change on Microcystis blooms in San Francisco Estuary are uncertain because factors associated with the abundance and distribution of Microcystis blooms since their inception in 1999 are poorly understood. Discrete and continuous data collected between 2004 and 2008 were used to assess what factors controlled bloom initiation and persistence, if there was an impact of the bloom on mesozooplankton abundance and toxicity or dissolved organic carbon concentration, and how these might vary with climate change. Microcystis abundance was greater in dry years than wet years and both total microcystins concentration and the microcystins content of mesozooplankton tissue increased with abundance. The bloom began in the upstream portions of the estuary and spread farther west during dry years. Bloom initiation required water temperature above 19°C and surface irradiance in the visible range above 100 W m −2 . The bloom persisted during a wide range of water quality conditions but was closely correlated with low turbidity. The intensity of Microcystis blooms will likely increase with climate change due to increased water temperature and low streamflow during droughts. Elevated water temperature earlier in the spring could also extend the duration of Microcystis blooms by up to 3 months.

Beschreibung: In pike E. lucius L., evidence on maternal effect on reproductive output is mixed. We studied whether older and larger pike females produce eggs and larvae of higher quality (weight, starvation resistance) in three forest lakes in southern Finland. Later, the study lakes were subjected to intensive experimental pike fishing, which we assumed would increase resource availability and lead to higher maternal investment (larger egg size). Length of female pike was positively correlated with the dry weight of eggs and larvae but this relation was dependent on female age. In old females, the effect of female length on egg weight was lower or even negative. Survival analysis showed a positive effect of female length on larval survival time indicating that larvae from larger females are less vulnerable to starvation during the early stage of life. After the intensive pike fishing, the positive effect of female length on egg weight was stronger in all age classes probably due to the released resources. Based on the high quality and amount of reproductive products in large (but not very old) females, they are important for the reproduction of pike populations. This should be considered in fisheries management.

Beschreibung: Freshwater predatory insects can exert strong effects on prey, although how multiple similar predators may coexist is not well understood. Larval predaceous diving beetles are often numerically and taxonomically abundant predators in lentic systems, but the proximate mechanisms that explain their high abundance remain unknown. Field surveys were conducted twice in June in ponds in Alberta, Canada to assess the associations between larvae of two genera ( Graphoderus , Rhantus ), their spatial locations, and correlations with potential prey. Both larvae were common and positively correlated within wetlands although neither varied with pond depth nor distance from edge. Laboratory trials indicated that Graphoderus consumed more prey (corixids) at the surface, whereas Rhantus killed benthic prey (chironomids) and corixids at an equal rate; damselflies were the least consumed prey. Predation also varied with depth, with both larvae feeding at higher rates in the shallowest environments compared to Graphoderus at an intermediate depth. Predator–prey correlations from ponds were mostly congruent with predation trials; Graphoderus was positively correlated with corixids, Rhantus was positively correlated with corixids and chironomids; beetles were uncorrelated with damselflies. Reliance on different prey in different microhabitats may be an important mechanism for the maintenance of high abundance of dytiscid larvae.

Beschreibung: In Chile, mediterranean climate conditions only occur in the Central Zone (ChMZ). Despite its small area, this mediterranean climate region (med-region) has been recognised as a hotspot for biodiversity. However, in contrast to the rivers of other med-regions, the rivers in the ChMZ have been studied infrequently, and knowledge of their freshwater biodiversity is scarce and fragmented. We gathered information on the freshwater biodiversity of ChMZ, and present a review of the current knowledge of the principal floral and faunal groups. Existing knowledge indicates that the ChMZ has high levels of endemism, with many primitive species being of Gondwanan origin. Although detailed information is available on most floral groups, most faunal groups remain poorly known. In addition, numerous rivers in the ChMZ remain completely unexplored. Taxonomic specialists are scarce, and the information available on freshwater biodiversity has resulted from studies with objectives that did not directly address biodiversity issues. Research funding in this med-region has a strong applied character and is not focused on the knowledge of natural systems and their biodiversity. Species conservation policies are urgently required in this highly diverse med-region, which is also the most severely impacted and most populated region of the country.

Beschreibung: Freshwater species worldwide are experiencing dramatic declines partly attributable to ongoing climate change. It is expected that the future effects of climate change could be particularly severe in mediterranean climate (med-) regions, which host many endemic species already under great stress from the high level of human development. In this article, we review the climate and climate-induced changes in streams of med-regions and the responses of stream biota, focusing on both observed and anticipated ecological responses. We also discuss current knowledge gaps and conservation challenges. Expected climate alterations have already been observed in the last decades, and include: increased annual average air temperatures; decreased annual average precipitation; hydrologic alterations; and an increase in frequency, intensity and duration of extreme events, such as floods, droughts and fires. Recent observations, which are concordant with forecasts built, show stream biota of med-regions when facing climate changes tend to be displaced towards higher elevations and upper latitudes, communities tend to change their composition and homogenize, while some life-history traits seem to provide biota with resilience and resistance to adapt to the new conditions (as being short-lived, small, and resistant to low streamflow and desiccation). Nevertheless, such responses may be insufficient to cope with current and future environmental changes. Accurate forecasts of biotic changes and possible adaptations are difficult to obtain in med-regions mainly because of the difficulty of distinguishing disturbances due to natural variability from the effects of climate change, particularly regarding hydrology. Long-term studies are needed to disentangle such variability and improve knowledge regarding the ecological responses and the detection of early warning signals to climate change. Investments should focus on taxa beyond fish and macroinvertebrates, and in covering the less studied regions of Chile and South Africa. Scientists, policy makers and water managers must be involved in the climate change dialogue because the freshwater conservation concerns are huge.

Beschreibung: Streams and rivers in mediterranean-climate regions (med-rivers) are subjected to sequential, yet contrasting hydrologic disturbances of drying and flooding. Although seasonally predictable, these disturbances can vary in intensity and duration within and among mediterranean-climate regions (med-regions). Consequently, med-rivers differ in the permanence of their aquatic habitats. To persist, species have acquired matched resistance and resilience adaptations. They gain resistance either by enduring the stress or avoiding it. Community recovery (or resilience) is achieved with cessation of hydrologic stress that permits maximization of re-colonization and reproduction. Endurance strategies are usually disturbance-specific, but avoidance enables organisms to cope with both drying and flooding, and is the prevalent resistance strategy. Correspondingly, community persistence depends to a large extent on the integrity of refuges, an aspect that has so far been little explored. Existing information suggests that seasonal community succession becomes more pronounced with increasing aridity and declining water permanence. The invertebrate community in semi-arid med-rivers can therefore undergo succession through three to four identifiable assemblages, whereas in perennial streams the difference between wet and dry period assemblages is smaller. Community turnover is influenced by the intensity of the hydrologic disturbances and varies between wet and drought years.

Beschreibung: Southwestern Australia is recognised as a global biodiversity hotspot, characterised by high diversity and endemism of vascular terrestrial plants. However, the significance of its freshwater biodiversity is not well understood. This review provides an updated account of species richness in rivers in the Mediterranean region (med-region) of southwestern Australia. Taxonomic knowledge of many aquatic invertebrate groups in this region has improved significantly in the last two decades as a result of ecological surveys and government funding for taxonomic research. Of the 662 species of plants and animals surveyed, 43% were found to be endemic to the region, yet when taxonomic groups were considered separately, levels of endemism were varied. To date, few aquatic species from the med-region are listed as threatened; however, many more species would be expected to be included if assessed against appropriate criteria. Conservation efforts are focussed on climate change mitigation and managing the impacts of broad scale land clearing for agriculture. Reserve design and location of important nature reserves on the extreme south coast, limits the ability for species’ movement to cooler, wetter regions. This will necessitate supporting restoration which leads to increased resilience in freshwater ecosystems to withstand the combined effects of climate change and land use.

Beschreibung: Rivers in mediterranean regions are subject to hydrological extremes. They range from highly stable, perennial ground- or snow-fed systems to highly ephemeral, unpredictable ones in semi-arid environments. Spatial and temporal complexity inherent in these systems presents challenges for ecological status assessment and defining reference conditions, particularly as many areas have been extensively transformed through anthropogenic activities. Temporal variability driven by sequential and predictable, seasonal events of flooding and drying accentuates the need to take season and/or hydrological period into account. Intermittent streams, which are common in mediterranean regions (med-regions) and which have aquatic communities distinct from perennial streams, are often not incorporated in bioassessment and present distinct challenges. Med-regions are also known for their high biodiversity and rates of endemism, as well as large numbers of introduced species. Med-regions are expected to be among the most affected by global climate change and, in these systems, climate change is an additional driver influencing ecosystems that are already stressed. From this review it is evident that an understanding of responses of indices, metrics, and models to climate change in comparison to existing stresses, and the development of thermally specific bioassessment tools are needed for this region.

Beschreibung: Refuges protect plant and animal populations from disturbance. Knowledge of refuges from disturbance in mediterranean climate rivers (med-rivers) has increased the last decade. We review disturbance processes and their relationship to refuges in streams in mediterranean climate regions (med-regions). Med-river fauna show high endemicity and their populations are often exposed to disturbance; hence the critical importance of refuges during (both seasonal and supraseasonal) disturbances. Disturbance pressures are increasing in med-regions, in particular from climatic change, salinisation, sedimentation, water extraction, hydropower generation, supraseasonal drought, and wildfire. Med-rivers show annual cycles of constrained precipitation and predictable seasonal drying, causing the biota to depend on seasonal refuges, in particular, those that are spatially predictable. This creates a spatial and temporal mosaic of inundation that determines habitat extent and refuge function. Refuges of sufficient size and duration to maintain populations, such as perennially flowing reaches, sustain biodiversity and may harbour relict populations, particularly during increasing aridification, where little other suitable habitat remains in landscapes. Therefore, disturbances that threaten perennial flows potentially cascade disproportionately to reduce regional scale biodiversity in med-regions. Conservation approaches for med-river systems need to conserve both refuges and refuge connectivity, reduce the impact of anthropogenic disturbances and sustain predictable, seasonal flow patterns.

Beschreibung: River and stream biofilms in mediterranean fluvial ecosystems face both extreme seasonality as well as arrhythmic fluctuations. The hydrological extremes (droughts and floods) impose direct changes in water availability but also in the quantity and quality of organic matter and nutrients that sustain the microbial growth. This review analyzes how these ecological pulses might determine unique properties of biofilms developing in mediterranean streams. The paper brings together data from heterotrophic and autotrophic community structure, and extracellular enzyme activities in biofilms in mediterranean streams. Mediterranean stream biofilms show higher use of peptides during the favorable period for epilithic algae development (spring), and preferential use of cellulose and hemicellulose in autumn as a response to allochthonous input. The drying process causes the reduction in bacterial production and chlorophyll biomass, but the rapid recovery of both autotrophs and heterotrophs with rewetting indicates their adaptability to fluctuations. Bacteria surviving the drought are mainly associated with sediment and leaf litter which serve as “humid refuges”. Some algae and cyanobacteria show resistant strategies to cope with the drought stress. The resistance to these fluctuations is strongly linked to the streambed characteristics (e.g., sediment grain size, organic matter accumulation, nutrient content).

Beschreibung: Mediterranean climate ecosystems are among the most fire-prone in the world; however, little is known about the effects of fire on mediterranean streams (med-streams). Fire impacts on med-streams are associated with increased runoff and erosion from severely burned landscapes during storms, particularly the first intense rains. Increased inputs of water, solutes, nutrients, sediment, organic matter, and ash to streams after fires are usually observed for months to up to 4 years. Return to pre-fire conditions is associated with vegetation recovery. Benthic algae, invertebrates, and fish are reduced to low levels by scouring floods after wildfire. If riparian zones are burned, benthic algae increase, and invertebrate communities become dominated by r -strategist species. Fishes are eradicated from reaches affected by intense wildfire and often do not re-colonize quickly because of downstream barriers. In general, med-stream communities appear to be more resilient to fire compared to streams in other ecosystems because of the rapid recovery of mediterranean upland and riparian vegetation and geomorphological conditions (1–4 years in med-streams vs 5–10 years in non-med streams). However, drought or mass sediment movements after fire can prolong fire effects. Studies of the long-term effects of fire and the consequences of fire management practices are still needed.

Beschreibung: Although the California mediterranean climate region is widely considered a biodiversity hotspot for terrestrial plants and vertebrates, freshwater biodiversity in this region is generally not well known. Using information from museum specimen databases, published literature, biological assessment surveys, and specialist’s knowledge, we review freshwater biodiversity for several groups of stream organisms in the med-climate region of California, which includes 2,220 species in 292 families. The groups with the highest diversity of lotic species are aquatic insects and diatoms, which comprise 39 and 36 % of species in our lists, respectively. Sequential floods and drying periods limit the overall biodiversity of many stream organisms in California mediterranean rivers, and continued climate and land-use change may cause disproportionate biodiversity declines in the region. However, only 4 % of lotic species have been evaluated in the IUCN Red List of Threatened Species, and many assessments are outdated. Future development of online databases for botanical and zoological collections will significantly enhance biodiversity and distribution knowledge. This information will enable us to more accurately and efficiently assess the effects of global change on biodiversity of freshwater organisms, to evaluate conservation status of individual taxa, and to set conservation priorities for stream ecosystems.

Beschreibung: The occurrence of picocyanobacteria, the smallest cell-size fraction of cyanobacteria, in low-pH waters, is still poorly studied. In this study, we tested the hypothesis that picocyanobacteria found occasionally in low-pH environments are adapted to such water conditions. We isolated picocyanobacteria by means of the cytometric method from two humic lakes with pH ≤5. We obtained two strains belonging to two cosmopolitan phylogenetic clades of picocyanobacteria: Cyanobium gracile cluster and Subalpine cluster I. Experiments on filtered lake water from low-pH (≤5) and slightly alkaline (pH 8.2) lakes, and with an acidified cyanobacterium medium (pH 4.5) were conducted to test the growth of the isolated picocyanobacteria in various pH conditions. The experimental results of this study showed that some picocyanobacteria strains were acid tolerant, achieving higher growth rates and reaching higher maximum numbers in humic, naturally acidic waters rather than in alkaline waters. We show that despite a close phylogenetic relationship, strains of picocyanobacteria exhibit significant physiological and ecological diversity and that at least some picocyanobacteria have the evolutionary potential to cope with low pH. Characterization of the genetic basis of acid tolerance in picocyanobacteria is important to understand how these microorganisms function in aquatic ecosystems and how their communities may respond to a changing environment.

Beschreibung: This paper summarises key issues from papers included in a special issue about the impacts of climate change on Australian wetlands. The papers covered: the assessment of wetlands under climate change, adaptation and engineering responses to climate change, and restoring wetlands under a changing climate. The key issues from these papers were used to indicate areas where the Ramsar Convention could develop guidance as part of its’ Handbooks for the Wise Use of Wetlands. These included: (i) assessing changes in the distribution of species and whether these constitute a change in the ecological character of the wetland; (ii) assessing the usefulness of models of wetland response to climate change; (iii) assessing the value in allocating water to protected sites where restoration would be contingent on reallocation of larger volumes of water; (iv) assessing the efficacy of engineering responses with the potential to deliver more water-efficient environmental outcomes for wetlands and (v) determining if the description of the ecological character of a Ramsar site at the time of listing is a suitable reference for management purposes. With these issues in mind it is recommended that further attention is directed towards determining and responding to the ecological consequences of climate change.

Beschreibung: A review of stratigraphic, radiocarbon, pollen, and aerial photographic data on the Swan Coastal Plain, south-western Australia, allows interpretation of long-term changes in climate and its effects on wetlands during the Holocene, whereas monitoring wetland hydrology and vegetation provides a measure of shorter-term changes. The information provides models for basin wetland response to changing climate. Drying climates shift wetlands to drier conditions, turning lakes into seasonally inundated or waterlogged basins, or resulting in an overall loss of wetlands, and favours more saline conditions, and development of carbonate deposits. Wetter conditions results in more frequent inundation, shifting damplands to sumplands or lakes, and resulting in fresher water conditions, and development of peat and/or organic matter enriched deposits. Examples of wetland basin responses to climate change across the Swan Coastal Plain show differential responses depending on setting, spatial distribution, hydrology, hydrochemistry and geochemistry, different temporal frameworks, and biological resilience.

Beschreibung: In Neotropical mangroves the crabs Ucides cordatus and Goniopsis cruentata have been considered the most significant propagule consumers, but their relative importance has not been investigated. The aim of this study was to compare the magnitude of predation by these crabs on three mangrove species propagules: Avicennia schaueriana , Laguncularia racemosa and Rhizophora mangle . We found that G. cruentata is a more important predator than U. cordatus in both natural and restored areas. We also tested the hypothesis that Ucides and Goniopsis have antagonistic effects on propagules predation using a cage experiment where the presence/absence of these species was manipulated in a 2 × 2 factorial design. The effects of Goniopsis were stronger in the absence of Ucides due to negative interactions between these predator species. Moreover, we found that Goniopsis preference for A. schaueriana and L. racemosa can favor the dominance of R. mangle in Neotropical mangroves. This study suggests that propagule predation by Goniopsis should be controlled in mangrove restoration programs at abandoned shrimp farms and destroyed areas, if dominance by R. mangle is undesirable relative to mixed species communities.

Beschreibung: We investigated the emergence of Daphnia pulicaria from resting eggs in Río Seco, an alpine lake in which the zooplankton growing period is short. In situ studies were carried out using sediment emergence traps and plankton sampling, and the sediment egg bank was analyzed. A laboratory experiment was performed to explore the role of photoperiod and temperature as hatching cues for D. pulicaria . We hypothesized that the time window for emergence would be short and that hatching cues would be linked to the variable ice-break period. In the field, D.   pulicaria showed a highly synchronized emergence in both years. The hatching period was restricted to 3 weeks during and immediately after the thaw. In the laboratory experiment, no hatchings were observed in the dark treatment and neither photoperiod nor temperature affected hatching rates. Therefore, the presence of light, which corresponds with the period of ice-break, was essential for triggering dormancy termination of D. pulicaria . Our results show that the period when the ice-break occurs is a key event for Daphnia population development. The longer ice-free periods predicted by climate change in the alpine lakes could therefore have important effects on the crustacean population dynamics of these systems.

Beschreibung: The objective of this research was to determine if the highly invasive round goby ( Neogobius melanostomus ) experiences lower predation risk during early stages of invasion. We compared round goby predation rates between a recently invaded area (occupied for ≈1 year) and a longer established area (≈7 years) of the Trent River, Ontario, Canada. Tethering trials were conducted in three habitat types, and comparable habitats in the two areas were similar in water temperature, velocity and depth. Predation rates of tethered round gobies were on average 27% lower in the recently invaded area. Reduced predation in the recently invaded area may be due to the short duration of round goby occupancy and/or differences in predator communities between the two study areas. Data before the round goby invasion suggest that predator communities were similar between the two range areas, but differences in predator abundance cannot be ruled out as a potential mechanism. Other possible mechanisms include a numerical or learned response by predators over time to a novel prey item. Reduced predation rate during the initial stages of invasion may contribute to the fitness of individuals that migrate into areas not previously occupied, and thus facilitate successful range expansion.

Beschreibung: Wetland managers are faced with an array of challenges when restoring ecosystems at risk from changing climate and human impacts, especially as many of these processes have been operating over decadal–millennial timescales. Variations in the level and salinity of the large crater lakes of western Victoria, as revealed over millennia by the physical, chemical and biological evidence archived in sediments, attest to extended periods of positive rainfall balance and others of rainfall deficit. The recent declines in the depth of these lakes have been attributed to a 15% decline in effective rainfall since AD 1859. Whilst some sites reveal state shifts following past droughts, the response of most wetlands to millennial-scale climatic variations is muted. Regional wetland condition has changed comprehensively, however, since European settlement, on account of extensive catchment modifications. These modifications appear to have reduced the resilience of wetlands limiting their capacity to recover from the recent ‘big dry’. These sedimentary archives reveal most modern wetlands to be outside their historical range of variability. This approach provides a longer-term context when assessing wetland condition and better establishes the restoration challenge posed by the impact of climate change and variability and human impacts.

Beschreibung: Globally, rain-fed wetlands provide critical habitat for a wide range of amphibian species, however, information on the use of rain-fed wetlands by Australian frog species is extremely limited. This study examined the distribution of frog breeding in rain-fed wetlands following the first significant rain event after a period of severe drought (2002–2009) in order to predict how frog communities may be affected in the future by changed climate. Tadpole communities along with vegetation and water quality variables were described in 35 rain-fed wetlands across the South West Slopes and Riverina bioregions of inland south-eastern Australia. In addition, weekly tadpole surveys were conducted in a subset of these wetlands to describe temporal patterns of occupancy. Despite the protracted dry period prior to this study 50% of the rain-fed wetlands surveyed contained tadpoles. However, frog communities were species poor with only five species recorded. The majority of wetlands were dominated be a single species, Limnodynastes tasmaniensis which is also common within permanent waterbodies such as farm dams and irrigation infrastructure in both bioregions. Tadpoles of two burrowing species L. interioris and Neobatrachus sudelli were restricted to a small number of wetlands mostly in the South West Slopes. The composition of tadpole communities changed over time, and Crinia parinsignifera was the only species that continued to breed over winter. The dominance of generalist species within rain-fed wetlands indicates that characteristics such as dispersal capability, flexibility in breeding times and the ability to utilise created habitats may be more important than burrowing ability and longevity when predicting vulnerability to climate change.

Beschreibung: Competing demands for water have resulted in many wetlands becoming either more permanently flooded or more permanently dry. It has been stated that such changes may lead to a loss of diversity in wetland communities; yet to date, this has not been tested experimentally. In this study, we experimentally test the hypothesis that increasing the hydrologic stability of wetlands results in reduced abundance, richness and diversity of aquatic biota emerging from wetland sediments. Sediment was collected from 19 wetlands that were divided into five groups (permanently flooded and wetlands that had been dry for 2, 7, 11 and 30 years). Aquatic plant communities germinating from the sediment of wetlands that had been permanently inundated and those that had been dry for 30 years had lower species richness and number of individuals than wetlands with intermediate flooding histories. For microfaunal communities, significantly less individuals but more taxa hatched from wetlands that had been permanently flooded or dry for 2 years than the other wetland groups. These results provide evidence of reduced biotic diversity as hydrological stability is increased under the common management scenarios of making wetlands more permanently wet or dry.

Beschreibung: Stoichiometric theory predicts that organisms should experience dietary imbalances not only when nutrients (e.g., phosphorus, P) are limiting relative to carbon (C), but also when nutrients are in excess (i.e., well above somatic demand). Nevertheless, few experiments have elucidated the response of consumers in such low C:P conditions. We assessed the growth, tissue stoichiometry, and nutrient excretion of the invasive primary consumer, zebra mussel (ZM), Dreissena polymorpha , under three dietary C:P conditions (C:P = 20, 45, 380) in the laboratory. The two low C:P conditions represent increasingly common eutrophic systems, while the high C:P treatment is representative of oligotrophic systems. Growth rates and condition were lower when ZMs were fed a low C:P (20 and 45) diet, compared to the C:P = 380 treatment, wherein ZMs grew rapidly and exhibited lower somatic C:P. Furthermore, ZMs in the C:P = 20 and C:P = 45 treatments excreted more ammonia indicative of protein catabolism. These results clearly show that hypereutrophic conditions invoke significant shifts in physiology, growth, and condition of ZMs. Together, these results are consistent with stoichiometric theory that predicts costs associated with the intake of excess dietary P.

Beschreibung: Despite over 100 years of phytoplankton research in the Baltic Sea, little is known about how the species composition has changed during this period, characterised by severe anthropogenic eutrophication. We investigated the phytoplankton communities in the northern Baltic Sea using data from 1903 to 1911 and 1993 to 2005; to minimise effects of methodological differences we focused on occurrence frequencies. We found that the historical and modern communities differed regarding both species composition and the relative importance of taxonomical groups. The most obvious differences were the increase of dinoflagellates and decrease in the diatom to dinoflagellate ratio in all seasons. Contrary to the widely held view that cyanophytes have gained significance, our results indicate that in terms of occurrence the group has not increased in summer, and has lost ground in both spring and autumn. Several shifts in the occurrence frequency and seasonality of individual taxa transpired. Examining our results in relation to environmental conditions we found that some changes may be symptomatic of climate change related pressures. However, statistical analyses revealed that an undefined ‘period effect’ was the most important factor separating the historical and modern phytoplankton communities. We interpret this ‘period effect’ as evidence for the direct and/or indirect influence of eutrophication.

Beschreibung: In Australia’s Murray–Darling Basin, small-scale engineering works called ‘environmental works and measures’ have been implemented as a basis for river and other wetland conservation. While implementing these, governments seem to have embraced the beguiling notion that scarce water supplies can be divided further, while conserving the environment and maintaining agricultural production. The difficulties in doing this are expected to increase in the face of extreme climate variability. With this scenario as a backdrop, the $280 million (Monetary values ($) in this paper are in Australian dollars (AUD). At the time of writing AUD $1.00 = ~USD $1.02.) Living Murray and related programmes are assessed to see whether microengineering works to manage the hydrology of wetlands make for effective adaptation to water scarcity and climate change or whether it amounts to an overly narrow adaptation or maladaptation. Some measures were found to be substantially beneficial, such as the construction of fishways. However, under these programmes, only 0.6% of the Basin’s wetlands would be inundated and there are significant risks including desiccation of non-target wetlands and further reductions in water allocations for the environment. It is recommended that trade-offs between alternative strategies are assessed as the basis for minimising perverse impacts under changing climatic and hydrological conditions.

Beschreibung: The purpose of this microcosm experiment was to determine whether the freshwater snail Bellamya aeruginosa affected phytoplankton community and water quality. Three treatments of different snail densities (low, medium, and high) and a control (no snails) were set up in twelve enclosures. Chlorophyll a (chl a ), transparency (SD), water temperature (WT), dissolved oxygen (DO), pH, nutrients, and abundance of phytoplankton were determined on days 0, 3, 7, 11, 15, 23, 31, 46, and 61. The total chl a concentration decreased and SD increased in the treatments, whereas the proportion of cyanobacteria chl a increased. Bellamya seemed to result indirectly in a decrease of DO, by reducing the algal biomass rather than by respiration. A significant decrease in nitrogen–phosphorus ratios was observed in the treatments. In the enclosed system the abundance of colonial green algae decreased over time whereas that of cyanobacteria and flagellates increased. Principal response curves showed that both phytoplankton community and water quality in the medium and high-density treatments were consistently different from in the control. These results indicate that the presence of snails resulted in a significant change of water physicochemical properties and phytoplankton community.

Beschreibung: Brown trout is a cold-adapted freshwater species with restricted distribution to headwater streams in rivers of the South European peninsulas, where populations are highly vulnerable because Mediterranean regions are highly sensitive to the global climatic warming. Moreover, these populations are endangered due to the introgressive hybridization with cultured stocks. Individuals from six remnant populations in Western Mediterranean rivers were sequenced for the complete mitochondrial DNA control region and genotyped for 11 nuclear markers. Three different brown trout lineages were present in the studied region. Significant genetic divergence was observed among locations and a strong effect of genetic drift was suggested. An important stocking impact (close to 25%) was detected in the zone. Significant correlations between mitochondrial-based rates of hatchery introgression and water flow variation suggested a higher impact of stocked females in unstable habitats. In spite of hatchery introgression, all populations remained highly differentiated, suggesting that native genetic resources are still abundant. However, climatic predictions indicated that suitable habitats for the species in these rivers will be reduced and hence trout populations are highly endangered and vulnerable. Thus, management policies should take into account these predictions to design upstream refuge areas to protect remnant native trout in the region.

Beschreibung: A rapid method to estimate the three-dimensional (3D) surface area (SA) of marine gorgonians and sponges from field measurements of colony height, diameter, and morphology was developed as an indicator of habitat availability for fish and invertebrates. Colony characteristics for sponges and gorgonians were compiled from field measurements, expert judgment, and taxonomic literature, and employed to generate 3D images using computer-aided design software. The images were used to test various statistical models and geometric surrogates that best estimated SA using only height and diameter measurements. A morphological classification system was devised using shapes and relative proportions of sponges and gorgonians which are commonly found in shallow waters (〈25 m depth) of the Central Western Atlantic Ocean. Regression models (linear, quadratic, or cubic) were found to be more robust than geometric surrogates, exhibiting greater accuracy at range extremes. Statistical models explained over 90% of the variation in SA and forecast errors of less than 20%. The best models for estimating SA are presented for eight sponge and nine gorgonian morphologies. Application of these methods with existing estimators for stony corals SA can be used as an indicator of structural habitat availability, which is an important ecosystem service of coral reefs.

Beschreibung: The common and routine procedure for the quantification of chlorophyll a (chl a ) in aquatic studies has a series of steps. Here, we sought to find optimal conditions for phytoplankton cell harvesting, chl a extraction, and chl a measurement and calculation, to find an effective, cost-saving, safe, and environment-friendly procedure for determining phytoplankton chl a concentration. We replaced the traditional GF/C filters with inorganic polymer flocculants (IPFs) and clay for phytoplankton harvesting, and then various solvents (acetone, ethanol, DMF, and DMSO), IPFs (PAC, PFS, and PAFS) and clay were tested for their suitability for chl a extraction, with or without homogenization at different temperatures for different extraction durations. About 0.3–1.0 g l −1 of PAC or PFSA combined with 1.0–2.5 g l −1 clay were found to provide optimal conditions in terms of yield and cost for phytoplankton cell harvesting from water samples. Based on our results, we recommend flocculation and centrifugation instead of glass-fiber membrane filtration for harvesting phytoplankton cells from environmental water samples, 95% ethanol for chl a extraction without homogenization and heating, and spectrophotometry to determine chl a concentration.

Beschreibung: Geomorphic research across the semi-arid and wet-dry tropics of northern Australia has highlighted the role of the regions’ estuaries as a “canary in the coalmine” for climate variations, with dramatic structural shifts over the Holocene. This behaviour highlights the region’s potential sensitivity to climate change and suggests the need for careful identification and interpretation of dynamics in the tropical and sub-tropical regions. However, analysis of change in these regions requires care, as a number of the basic tools applied to interpreting estuarine change in temperate regions are obscured, invalid or simply unavailable when applied in lower latitudes. This study provides a synthesis from a range of investigations across northern Australia and identifies characteristics to be considered when interpreting or predicting sub-millennial estuarine change in these regions.

Beschreibung: Zooplankton are potentially powerful proxies for the assessments of biologic integrity. The paleolimnological perspective and use of fossil Cladocera also provide the means to reconstruct reference conditions and natural long-term community dynamics. Unfortunately, the use of zooplankton in lake quality assessments is currently underexploited. We studied a surface sediment dataset of 41 lakes in Finland to examine the relationship between Cladocera remains and environmental variables. Of the examined environmental variables, total phosphorus availability was found to be the most important variable in explaining the Cladocera community composition. Following the tests on species environment relations, we selected a lake trophic typology as the most suitable environmental variable for developing a new tool for limnoecological quality assessments. A test of the model on a modern and historic sample from a eutrophied lake showed that the test lake has proceeded from “mesotrophic/poor” to “eutrophic/bad” limnoecological state in agreement with previous independent evidence. The model developed here showed favorable performance that can be used to provide reliable estimates of ecological and environmental state of lakes.

Beschreibung: Nutrient enrichment may alter population dynamics of species in different ways depending on their life strategies. The aim of this study was to test the effect of different nutrient concentrations on the population development of two bacterivorous freshwater nematodes, Bursilla monhystera and Plectus aquatilis . Microcosms with autoclaved natural sand from a pristine stream (Fuirosos, NE of Spain) were enriched with different levels of phosphate, nitrate and ammonia as inorganic nutrients and glucose as a biodegradable dissolved organic carbon source. Although leaching of carbon and nutrients from the detritus fraction in the sediment initially may have overruled differences between treatments, later samplings revealed bottom-up control, with Bursilla monhystera abundances positively correlated to bacterial abundances at high nutrient concentrations. Nevertheless, there were several indications that nematodes in turn affected microbial abundance, most likely through excretion of ammonia and through grazing. In contrast to B. monhystera , Plectus aquatilis at high nutrient concentrations showed a unimodal abundance curve, while not increasing in abundance at low nutrient concentrations. Glucose enrichment did not have any stimulatory effect on either microbial or nematode abundances, probably as a result of unfavourable C:N:P stoichiometry. P enrichment, by contrast, stimulated microbial and Bursilla abundances. Our results indicate that episodic nutrient enrichment may affect populations of bacterial-feeding nematodes in the short term. Their longer-term dynamics may, however, be more dependent on leaching of carbon and nutrients from the pools of sediment-bound detritus.

Beschreibung: This study investigates the dynamics of protozoan community in biofilms formed on inert artificial surfaces suspended in various freshwater environments. The results also test the hypothesis that the dynamics of protozoan and microalgal communities in biofilms are interdependent because the latter form one of the major food items of benthic protozoa. Cleaned glass slides were suspended in surface waters at four sampling locations to collect biofilm communities. The glass slides after retrieval were observed under a microscope for diatom and protozoan density and their generic composition. Members of protozoa belonging to phylum Sarcomastigophora dominated the protozoan community followed by phylum Ciliophora in all sampling locations. The variation of protozoan feeding groups showed an initial abundance of autotrophs/holophytes which gave way to heterotrophs, predators, and bacterivores towards the end of the study. The density and generic composition of protozoa varied significantly with the age of biofilm and sampling location. The density variation of protozoa followed that of diatoms in all four sampling locations and this has resulted in a significant positive correlation between diatom and protozoan densities. This suggests the dependency and/or food web connectedness of these two communities in natural biofilms.

Beschreibung: Nutrient ratios have been related to nutrient limitation of algal growth in lakes. Retention of nutrients in lakes, by sedimentation and by denitrification, reduces the nutrient concentrations in the water column, thereby enhancing nutrient limitation. Differential retention of nitrogen and phosphorus alters their ratios in lakes and thereby contributes to determine whether nitrogen or phosphorus limits algal growth. We examined the relationships between differential nutrient retention, nutrient ratios, and nutrient limitation in Lake Brunner, a deep oligotrophic lake. The observed retention of nitrogen (20%) and phosphorus (47%) agreed with predictions by empirical equations from literature. As a result of differential retention with a much larger proportion of phosphorus retained than that of nitrogen, the nitrogen:phosphorus ratio was higher in the lake (69) than in the inflows (46). While the mean ratio in the inflows suggested no or only moderate phosphorus limitation, the lake appeared to be severely phosphorus limited. Combining empirical equations from literature that predict nitrogen and phosphorus retention suggests that the nitrogen:phosphorus ratio is enhanced by greater retention of phosphorus compared to nitrogen only in deep lakes with relatively short residence times, such as Lake Brunner. In contrast, in most lakes differential retention is expected to result in lower nitrogen:phosphorus ratios.

Beschreibung: Using a large pan-European dataset, we compared least disturbed sites to sites impacted by human pressures across broad river types to assess which aspects of bio-ecological traits of the fish assemblage are most sensitive to alterations of the river ecosystem. To control for variation across river types and large-scale environmental gradients, we began by clustering the least disturbed sites ( n  = 716) into four homogenous fish assemblage types (FATs) differing by four fish metrics, i.e., lithophilic, rheophilic, omnivorous, and potamodromous fish. We predicted these FATs (headwater streams, medium gradient rivers, lowland rivers, and Mediterranean streams) using environmental variables, i.e., altitude, river slope, temperature, precipitation, latitude, and longitude for impacted sites in our dataset ( n  = 2,389). Using tests of sensitivity and intensity, 17 fish metrics showed a clear reaction to human pressures. However, 12 metrics responded exclusively within only one of the four FATs. Hence we observed a divergent reaction of fish metrics to human pressures in, e.g., headwater versus lowland rivers. Type-specific reactions are useful in customizing impact assessment for particular river types. It is of primary importance to understand the comparative sensitivity and efficiency of fish-based indicators of water quality for detecting human-induced degradation of river ecosystems.

Beschreibung: To elucidate the effects of scallop mariculture on the macrobenthic community in a moderate energy system, bimonthly samples from four transects along a distance gradient in Sishili Bay, the northern Yellow Sea of China, were investigated. Differences in macrobenthic community structure along the distance gradient were evaluated using univariate and multivariate analyses. The AZTI’s Marine Biotic Index (AMBI) and multivariate-AMBI analyses indicated that the macrobenthic community suffered little disturbance from the scallop culture. Consistently, the results of two-way analysis of similarities demonstrated that macrobenthic communities showed no difference along the distance gradient, but were significantly affected by the sampling months and transects. This conclusion was also confirmed by other univariate and multivariate analyses. The concentration of total organic carbon was 17.27 ± 6.05 mg g −1 , which is below the dangerous threshold of 35 mg g −1 toxic to benthic fauna. Combined results revealed that no detectable effects on the macrobenthic community were caused by intensive and long-term scallop culture in this moderate energy system. This is likely due to the influence of local hydrodynamics and it is recommended that intensive scallop farming be located in areas with strong tidal or current flows.

Beschreibung: Southwestern Australia has already undergone significant climatic warming and drying and water temperatures are increasing particularly in small streams where riparian vegetation has been cleared. The ability to predict how freshwater fauna may respond to these changes requires understanding of their thermal tolerances. A review of relevant literature and laboratory testing of four aquatic species from southwestern Australia were used to compare upper thermal tolerance (UTT) among key taxonomic groups. UTT for selected species determined by LT 50 tests were similar to that of species tested elsewhere. Mean UTT, based on relevant literature and LT 50 experiments, ranged from 22.3°C for Ephemeroptera to 43.4°C for Coleoptera. Mean UTT for both Coleoptera and Odonata (41.9°C) were significantly higher than those for all the other groups (22.3–31.5°C) with the exception of Planaria. The mean UTT value of 22.3°C for Ephemeroptera was significantly lower than for Decapoda (29.6°C), Trichoptera (30.1°C) and Mollusca (31.5°C). For three insect orders tested, eurytherms had significantly higher UTT values than stenotherms. The variation in UTT among taxa suggests that additional thermal shifts, caused by riparian disturbance and/or climate change, are likely to create novel assemblages due to the replacement of temperature-sensitive taxa by more tolerant taxa. This has implications for the sustainability of regionally important endemic cool water species.

Beschreibung: The effects of stream urbanization on fishes have been well studied in general. Yet despite the wealth of knowledge available for streams in many different ecoregions, relatively little is known of the effects of urbanization on prairie stream fishes. Management of urban stormwater through impoundment has the potential to fragment streams, and habitat fragmentation on nonurban streams has been documented to relate to declines in small-bodied mobile minnow species. We asked whether urban habitat fragmentation through stormwater impoundment would relate to a similar decline in small-bodied fishes in Cottonwood Creek, a stream system partially managed by stormwater impoundment in central Oklahoma. Analyses with basic metrics of ecological tolerance, richness, community structure, and multivariate ordination found negative relationships between cyprinid richness and abundance and a metric of urban habitat fragmentation, as well as between Lepomis humilis , a small-bodied sunfish, and the metric of urban habitat fragmentation. We review potential hypotheses for these biological patterns in fragmented urban streams, including predation, lack of successful reproduction, and lack of ability to recolonize above barriers.

Beschreibung: While numerous reports exist on the results of lake restoration initiatives in temperate regions, only a few exist from subtropical lakes. We present results of the lake restoration of shallow, subtropical Lake Wuli, China, conducted between 1999 and 2010. After restoration, annual average concentrations of total nitrogen, total phosphorus (TP), and chlorophyll a and the chemical oxygen demand declined significantly, though summer TP remained high. Suspended solids increased significantly over the years, whereas transparency decreased, though not significantly so. The contribution of cryptophytes to total phytoplankton biomass decreased, while the proportion of cyanobacteria, especially potentially N 2 -fixing species, increased. Rotifers were superseded by crustaceans as the dominant taxon of the zooplankton community. Enhanced abundance of Daphnia spp., appearance of Leptodora kindti , and increased biomass ratios of zooplankton to phytoplankton, calanoids to cyclopoids, and nauplii to copepods in the post-restoration period indicate reduced fish predation and stronger top-down control of phytoplankton. However, the increase in non-algal turbidity, probably caused by the higher biomass of benthivorous fish, apparently prevented the re-establishment of submerged macrophyte communities. We conclude that removal of fish, particularly benthivorous species, will further improve water quality in this and other subtropical shallow lakes.

Beschreibung: Agricultural and urban runoffs result in increased nitrogen and phosphorus inputs in rivers and are the cause of eutrophication. Headwater streams are less frequently affected by these impairments because of the low-to-moderate human activities there. Eutrophication can affect the structure and function of benthic communities in headwater streams, stimulating the activity of heterotrophic microorganisms and macroinvertebrates on a pivotal process such as leaf-litter decomposition. In this study, we monitored the breakdown of alder leaves in six headwater streams that constitute a moderate nutrient enrichment gradient. Breakdown experiments were conducted in autumn–winter and leaf carbon, nitrogen and phosphorus, and associated aquatic hyphomycetes and macroinvertebrates were determined. The increase in nutrient availability in the stream water enhanced leaf-litter quality and led to an increase in the hyphomycete assemblage evenness and a reduction of shredder densities. However, contrary to our expectations, dissolved nutrient availability did not explain the breakdown rates. Thus, the absence of a clear effect of nutrient enrichment of stream water on the leaf breakdown rate highlights the difficulties of predicting the response of this ecosystem process to slight levels of eutrophication in headwater streams.

Beschreibung: The axolotl ( Ambystoma mexicanum ) is a critically endangered and threatened species endemic of the Central Valley of Mexico. The population of this neotenic amphibian has declined in recent years as a result of habitat destruction, polluted waters, and the introduction of exotic species such as tilapia. We evaluated the antipredator response of predator-naïve axolotls to visual and chemical cues of the Nile tilapia ( Oreochromis niloticus ) and its foraging consequences. Axolotls decreased their activity and increased their use of refuge in the presence of combined chemical and visual cues from the predator. The axolotls seem to use their vision to confirm the level of risk perceived through chemical signals to modulate their antipredator response accordingly. The axolotls engaged in prey capture at a similar rate independent of the type of predator exposure. However, the efficiency of prey capture decreased in axolotls exposed to the chemical and the combined visual and chemical cues from the tilapia. The foraging costs to the axolotls induced by tilapia can ultimately affect their growth rate and size. The axolotls display antipredator behaviours to reduce the risk of predation by tilapia, which is a primary condition of coexistence with this exotic predator.

Beschreibung: The effects of droughts on benthic infaunal communities and three epifaunal species were determined in three semi-arid central Texas estuaries with different inflow dynamics and consequent salinity regimes: the Nueces, Lavaca-Colorado, and Guadalupe Estuaries. Periods (months or years) were considered to be in drought if mean salinities were in the upper quartile of historic salinities. This drought classification method was verified by comparing the Palmer Drought Severity Index of the catchments with the drought classifications within each estuary. Droughts have demonstrable effects on estuary water column condition, notably decreases in turbidity, nutrient concentrations, and chlorophyll concentrations. Droughts do not appear to be important drivers of infaunal communities in estuarine regions with normally high salinities (25–32) although they coincide with increased diversity and changes in community composition in estuarine regions that have lower salinities (10–19). Droughts cause decreases in Litopenaeus setiferus (white shrimp) and Callinectes sapidis (blue crab) abundances and spatial extents. This indicates that droughts, especially when combined with water diversions, may negatively affect primary and secondary productions in other semi-arid estuaries of the world.

Beschreibung: Lake Griffin received discharges for decades from muck farms developed on former floodplain wetlands, leading to hypereutrophic conditions. Management actions included wetland restoration of farmland to reduce nutrient discharges, and harvesting of gizzard shad to remove nutrients in fish biomass and reduce nutrient recycling from sediments. Despite a reported susceptibility to wind-driven sediment resuspension, there have been substantial improvements in water quality in Lake Griffin, including decreases in nutrient concentrations, chlorophyll- a , and cyanobacterial biovolume, and increases in water transparency. Water quality improvements in Lake Griffin were substantially greater than occurred in ten comparison lakes. External nutrient load reduction was the primary factor contributing to water quality improvement, although there was evidence of an effect of shad harvesting, including correlations between shad catch per unit effort and nutrient concentrations, and an estimated effect of biomass removal and recycling reduction accounting for about 40% of the external load during the harvest period. Net production of total nitrogen in the lake was strongly related to external total phosphorus loading, indicating phosphorus limitation of nitrogen fixation. The response of Lake Griffin indicates that the combination of external nutrient load reduction and biomanipulation can result in sustained improvements in water quality in shallow subtropical lakes.

Beschreibung: The objective of this study was to evaluate the response of stream diatom assemblages to changes in water quality in different land-use settings. Water quality sampling and benthic diatom community data were collected in April and September 2013 at 95 sampling stations in the Manyame Catchment, Zimbabwe. The data collected were subjected to multivariate statistical techniques; CCA and cluster analysis to determine environmental gradients along which the diatom species were distributed as well as to elucidate hypothesized differences in community structure per land-use type. Three land-use categories were identified in this study: commercial agricultural, communal agricultural and urban-mining areas in order of increasing human disturbance. No significant differences in physical and chemical variables were recorded between the two sampling periods. Study sites were grouped into roughly three broad categories based on CCA and cluster analysis. As pollution increased, low to moderate pollution tolerant species such as Cocconeis placentula , Surirella linearis and Surirella robusta were replaced by high pollution tolerant species such as Pinnularia braunii , Tryblionella coarcata , Luticola goeppertiana and Stauroneis smithii . This shows that diatom assemblages are potential indicators of changes in water quality due to changes in catchment land-use.

Beschreibung: Trait patterns can give insights into how communities assemble under a functional perspective. We constructed a rotifer trait matrix related to food acquisition and predator defence and calculated Rao’s quadratic entropy ( Q ) as an index of functional diversity to investigate trait patterns in different layers (0–2, 5–35, 0–35 m) for a 5-year dataset of Lake Tovel, Italy. Trait patterns were determined by comparing Q observed to Q from random communities. While trait patterns can be determined by species traits, richness, and abundance, in most samples, irrespective of layer, trait patterns could be solely attributed to traits indicating their importance for community assembly. Trait convergence dominated in the upper layer, while trait divergence dominated in the lower layer. Using logistic regression, we related trait patterns to environmental parameters. In the lower layer, trait divergence was linked to competition for food while trait convergence was linked to copepod predation. However, in the upper layer neither competitors nor predators influenced trait patterns, and we suggest that ultraviolet radiation and temperature were the main drivers of trait convergence. Our study indicated that environmental filtering drove rotifer trait patterns in the upper layer, whereas species interactions drove trait patterns in the lower layer.

Beschreibung: Herbivore impacts on macrophyte growth vary with the identity of the herbivores and macrophytes, as well as under different abiotic conditions. This interaction is further complicated by anthropogenic alterations to the environment, such as eutrophication. In this study, we utilized in situ herbivore exclusion experiments and mesocosm feeding preference assays to examine the impacts of different herbivores on the growth of two morphologically similar, co-occurring macroalgal bloom Ulva species in a nutrient-rich environment. We found that herbivory had a measurable impact on Ulva biomass, though the rate of consumption rarely surpassed growth for either Ulva species. We determined that the primary herbivores within the blooms were amphipods and mud crabs, and that their effects varied among study sites and months. Our results also confirmed that, even with a diverse suite of consumers, Ulva blooms are capable of escaping herbivore control, particularly early in the growing season when growth rates peak and herbivore activity is limited. Furthermore, our experiments revealed species-specific feeding preferences among herbivores, as well as differences in growth rates and chemistry between the two Ulva species, which likely influence bloom dynamics.

Beschreibung: This study analyzed variation in stable isotope ratios of aquatic and terrestrial primary producers and two common cyprinid fishes ( Capoeta banarescui and Squalius cephalus ) at seven sites in the upper Yeşilırmak River Basin, Turkey, to estimate relative contributions of basal production sources to fish biomass. We hypothesized that seasonal and spatial variation in fish assimilation of basal production sources would be affected by hydrological variation, with results for a reach downstream from a reservoir differing from those from upstream sites. Carbon and nitrogen isotopic ratios of primary producers and S. cephalus and δ 15 N of C. banarescui revealed significant spatial variation. δ 13 C of primary producers, δ 15 N of S. cephalus , and both δ 13 C and δ 15 N of C. banarescui revealed significant seasonal variation. C. banarescui biomass in the river channel was mostly derived from terrestrial herbaceous plants, and its biomass in the reservoir derived mostly from aquatic plants. Estimated proportional contributions of herbaceous plants to both species were greatest at the downstream site during spring, and declined during summer in the case C. banarescui . Overall, the influence of the dam was small relative to effects from watershed characteristics and seasonal changes in temperature and hydrology.

Beschreibung: Patterns of association between functional traits and environmental gradients can improve understanding of species assemblage structure from local to regional scales, and therefore may be useful for natural resource management. We measured functional traits related to trophic ecology, habitat use, and life-history strategies of fishes and examined their associations with environmental factors in the Brazos and Trinity River basins in Central Texas. We also examined the relationship between functional diversity of fish assemblages and indices of biotic integrity and habitat quality. Environmental characteristics at the local reach and catchment scales, including the extent of forested area in the watershed, amount of land developed for urban and agricultural uses, stream size, substrate characteristics, and availability of riffle and pool habitats, were significantly associated with functional trait composition of fish assemblages. Broad physiographic differences between ecoregions also had a large influence on taxonomic and functional assemblage structure. In general, the volume of functional trait space occupied by fish assemblages was greatest in streams with high habitat quality scores located within landscapes having less alteration from agriculture and urban development. Distributions of functional traits in fish assemblages might provide an additional basis for assessment of stream condition in relation to environmental impacts.

Beschreibung: Floods are major determinants of ecological patterns and processes in river-floodplain systems. Although some general predictions of the effects of water level changes on ecological attributes have been identified, specific tests using the flood pulse concept are scarce, mainly in tropical areas, where large river-floodplain systems abound. We tested the hypothesis that floods decrease environmental and biological variability using data from a near-pristine floodplain in Central Amazon (Brazil). We recorded nine limnological variables and the zooplankton community structure at eleven sites during one low and one high water period. During the low water period, when the levels of hydrological connectivity were low, asynchronous processes (e.g., sediment disturbance by biota, decomposition, and predation) likely determined the large environmental and biological heterogeneity in the floodplain. On the other hand, environmental variability and zooplankton beta diversity were significantly decreased by the flood. We postulate that floods act as “rubber erasers”, reducing the environmental and ecological idiosyncrasies created during low water periods. Also, we suggest that dilution effects and enhanced connectivity during the high water period, along with species sorting during the low water period, may determine zooplankton beta diversity patterns in river-floodplain systems.

Beschreibung: Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances.

Beschreibung: In warm lakes, fish aggregate within macrophytes, thereby weakening the role of these as a daytime refuge for zooplankton and altering the zooplankton size structure, predation pressure, and water clarity. To elucidate the role of macrophytes as a refuge for zooplankton and their effect on zooplankton size distribution, we established three sets of strandardized artificial plant beds in 11 lakes in Turkey with contrasting fish predation risk and turbidity. Zooplankton were sampled within and outside of each plant beds during day and night. Fish, collected overnight in multimesh-sized gillnets, were abundant both inside and outside the artificial plant beds, impoverishing the usefulness of plants as a daytime refuge for particularly large-bodied zooplankton. Zooplankton size diversity was negatively related to fish abundance. Diel vertical migration was the frequent anti-predator avoidance behavior, but reverse migration was also observed when Chaoborus was present. In contrast to the small-bodied taxa, large- and medium-sized taxa showed intraspecific size-based migration (i.e., individuals of different sizes had different migration patterns). Predators influenced the size structure and diel movement of zooplankton, but the response changed with the size of zooplankton and water clarity.

Beschreibung: Anthropogenic nutrient enrichment of forested headwater streams can enhance detrital quality, decrease standing stocks, and alter the community structure of detrivorous insects, reducing nutrient retention and decreasing ecosystem functioning. Our objective was to determine if stoichiometric principles could be used to predict genus-specific shifts in shredding insect abundance and biomass across a dissolved nutrient and detritus food quality/quantity gradient. Detritus, insect, and water samples were collected from 12 Ozark Highland headwater streams. Significant correlations were found between stream nutrients and detrital quality but not quantity. Abundance and biomass responses of four out of five tested genera were accurately predicted by consumer-resource stoichiometric theory. Low carbon:phosphorus (C:P) shredders responded positively to increased total phosphorus and/or food quality, and high C:P shredders exhibited neutral or negative responses to these variables. Genus-specific declines were correlated with decreased overall biomass in shredder assemblages, potentially causing disruptions in nutrient flows to higher level consumers with nutrient enrichment. This work provides further evidence that elevated nutrients may negatively impact shredding insect communities by altering the stoichiometry of detritus–detritivore interactions. A better understanding of stoichiometric mechanisms altering macroinvertebrate populations is needed to help inform water quality criteria for the management of headwater streams.

Beschreibung: pH and water hardness are considered to be important factors for population dynamics in crustaceans. In this study, the effects of pH (6, 7, 8, and 9) and water hardness (40 mg CaCO 3 /l and 160 mg CaCO 3 /l) on the growth and reproductive response of the freshwater ostracod Heterocypris incongruens Ramdohr were investigated. Heterocypris incongruens exposed to a pH level of 6 or 7 had a slower growth rate and shorter carapace length than those exposed to high pH levels. The reproductive output of H. incongruens was higher under hard water conditions. However, there were no significant differences in the effects of pH and water hardness on the egg hatching rate. Consequently, higher pH levels and water hardness resulted in increased population growth rates. Collectively, the results indicate that variations in pH levels and water hardness lead to changes in the life history characteristics of H. incongruens . These characteristics provide a mechanistic explanation for habitats in which H. incongruens can persist.

Beschreibung: Artificial reefs have been deployed in France since 1968 with the principal objective of enhancing success and continuity of artisanal fishing. Over 50 % of the volume of reef material has been deployed since 2000. Because of significant expansion of reef construction and availability of new research results concerning their performance since the late 1990s, we examined status and trends of French artificial reefs. Since the review of Barnabé et al. (Artificial reefs in European seas, 2000 ), 35 reports have been published and are analyzed here. Fish assemblages on artificial reefs have been the focus of ecological research, with emphasis on species richness and abundance. Fish production has been associated with the age of artificial reefs and the reef’s structural complexity. The perception of stakeholders toward artificial reefs is a notable area of investigation. Economic studies are absent. Other developments in French artificial reefs over the last 10–15 years include the discontinued use of waste materials in reef construction, more directed design of reef structure, and the inclusion of additional objectives concerning biodiversity and recreation. Recommendations here include development of long-term ecological studies of artificial reefs and the evaluation of fishery production, including issues such as trophic dynamics, ecological connectivity of habitats, and socio-economic studies.

Beschreibung: The reproductive and general health of exploited fish stocks is an essential element of sustainable and profitable fisheries. The main purpose of this study was to assess the relationships between reproduction and two important parameters of fish health (parasitism and energy reserves) in female specimens of red mullet, Mullus barbatus , from the western Mediterranean Sea. We present new data for this species on (i) the prevalence and intensity of infection by metazoan parasites; (ii) the total lipid content in muscle and gonads as a measure of condition and (iii) fecundity and egg quality as a measure of their reproductive capacity. The results show that M. barbatus is a batch spawner with an income breeding strategy, an asynchronous development of oocytes and indeterminate fecundity. The results also indicate that the three most abundant and prevalent parasites significantly affect the condition and reproduction of M. barbatus . Specifically, the digenean, Opecoeloides furcatus , causes a reduction in the female’s energy reserves, while the nematodes, Hysterothylacium fabri and H. aduncum , produce a rise in egg production but impair egg quality. These implications of the relationships between parasitism, fish health and fish reproduction should be taken into consideration in the assessment and management of exploited species.

Beschreibung: Terrestrial runoff into aquatic ecosystems may have both stimulatory and inhibitory effects, due to nutrient subsidies and increased light attenuation. To disentangle the effects of runoff on microbenthos, we added soil to coastal mesocosms and manipulated substrate depth. To test if fish interacted with runoff effects, we manipulated fish presence. Soil decreased microphytobenthic chlorophyll-a per area and per carbon (C) unit, increased microbenthic phosphorous (P), and reduced microbenthic nitrogen (N) content. Depth had a strong effect on the microbenthos, with shallow substrates exhibiting greater microbenthic net ecosystem production, gross primary production, and community respiration than deep substrates. Over time, micobenthic algae compensated for deeper substrate depth through increased chlorophyll-a synthesis, but despite algal shade compensation, the soil treatment still appeared to reduce the depth where microbenthos switched from net autotrophy to net heterotrophy. Fish interacted with soil in affecting microbenthic nutrient composition. Fish presence reduced microbenthic C/P ratios only in the no soil treatment, probably since soil nutrients masked the positive effects of fish excreta on microbenthos. Soil reduced microbenthic N/P ratios only in the absence of fish. Our study demonstrates the importance of light for the composition and productivity of microbenthos but finds little evidence for positive runoff subsidy effects.

Beschreibung: Tidally driven fluctuations lead to rapid variations in hydrological properties that can have profound effects on the dynamic and functions of salt marshes. During low tides, many nektonic species find refuge from predatory fish in shallow intertidal pools. The utilization of shallow pool refuges also exposes fishes to fitness costs that fluctuate between day and night. Yet, how aggregated fish using an intertidal pool modulate their schooling behavior over the diel cycle remains unknown. Using high-resolution imaging sonar (ARIS), we monitored an intertidal pool over a 3-day period and quantified fish abundance, size, and schooling behavior relative to the diel and tidal cycles. Higher fish abundance was found during low tides than high tides when the section was connected with the subtidal waters. At low tide, no differences in fish abundance and size were detected in the pool between day and night, but larger schools formed at night than day. Our results suggest that biotic and abiotic factors affecting fish schooling behavior in the low tide refuge may vary over the diel cycle. We present possible functional explanations for the shifts in schooling tendency between nocturnal and diurnal utilization of the pool.

Beschreibung: Anthropogenic changes to the temperature regimes of rivers, whether through thermal pollution, removal of shade, or climate change, could affect community stability and cause phenological changes in aquatic species. This study examines the impact of a thermal discharge from a power station on the diversity and composition of the aquatic macroinvertebrate community in the River Severn, UK. Daily temperatures up to 2 km downstream of the thermal discharge averaged 4.5°C above ambient. Abundance and taxon richness metrics were reduced at a site approximately 0.5 km downstream of the power station outfall, but were largely unaffected at a second site about 2 km downstream. The majority of the macroinvertebrate taxa observed were recorded at both control and heated sites, suggesting species were below their thermal tolerance threshold or had developed adaptations to survive increased temperatures. However, indicator species analysis suggests certain taxa were associated with particular sites; abundances of Musculium lacustre , Simulium reptans , and Orthocladiinae were greater at the unheated control site, whereas more pollution-tolerant species such Asellus aquaticus and Erpobdella octoculata were more common in the thermally impacted reaches. Overall, the results provide an indication of potential species and community response to future warming under climate change scenarios.

Beschreibung: Light, temperature, and the availability of carbon are three major drivers of submerged plant growth, photosynthesis, and competitive strength. A laboratory study using a three factorial experimental design (light × temperature × CO 2 ) was carried out to evaluate growth responses (RGR (relative growth rate), LDMC (leaf dry matter content), and root:shoot ratio) and physiological changes (pigment characteristics and net photosynthesis under CO 2 depletion) in the European native Myriophyllum spicatum and the non-native invasive M. heterophyllum to changes in the three variables. Both species showed temperature optima of 21°C and highest growth rates under high-light and high CO 2 conditions. Additionally, the capacity of both to use \({\text{HCO}}_{3}^{ - }\) was significantly higher in plants acclimated to CO 2 depletion than for plants growing in CO 2 -rich water. Summarizing, both species showed their ability to grow under variable conditions, but M. spicatum is the better \({\text{HCO}}_{3}^{ - }\) user and showed better acclimation in growth and physiological parameters to CO 2 depletion. Overall, native M. spicatum reached higher growth rates and showed a better acclimation to low CO 2 conditions than the non-native M. heterophyllum. Thus, the \({\text{HCO}}_{3}^{ - }\) use capacity alone cannot explain the success of evergreen M. heterophyllum in formerly M. spicatum -dominated waters.

Beschreibung: The ability to respond to a predation threat may be the key factor influencing prey survival. Thus, small-sized fish may adapt to use macrophyte patches as refugia in ecosystems where they face predators. We evaluated the habitat choices of a small fish species ( Serrapinnus notomelas ) to determine whether these fish prefer native versus recently introduced submerged macrophyte stands in the context of predator avoidance. Specifically, we applied three predator cue treatments: no cue, chemical cue from a hungry predator and presence of a satiated predator. First, we empirically tested the theoretical assumption that the prey fish use vegetated habitats and that the presence of an actual predator has a stronger effect on the choice of habitat than simply a chemical cue. Then we tested the hypothesis that prey do not choose a habitat according to macrophyte species and whether this pattern changed as a result of increasing predation risk. We found that the prey fish preferred vegetated habitats; however, they did not appear to distinguish native from invasive macrophytes. Our results support the hypothesis that the physical structure of macrophytes is more important in determining habitat choice than the evolutionary relationship between the fish and the native macrophyte species.

Beschreibung: The introduction of Cichla kelberi to the Rosana Reservoir (Paraná River basin, Brazil) was followed by a substantial loss of fish diversity in macrophyte patches, and this study investigated the hypothesis that C. kelberi was the driver of faunal disassembly via certain demographic dynamics (i.e. a pulse of juvenile fish). We analysed the variation in the structure of fish assemblages, the abundance of C. kelberi and habitat quality between 2003 and 2007, including time points that preceded and followed the introduction of the predator. A stepwise regression analysis showed that macrophyte biomass was positively correlated with assemblage attributes (richness and abundance), whereas C. kelberi density showed a strong negative correlation. Variables related to habitat quality were not included in the model, and exhibited little variation over the study years. As predicted, the density of small-bodied fish was negatively associated with the pulse of juvenile C. kelberi , and a tethering experiment revealed that predation pressure increased in the macrophyte patches when young C. kelberi were abundant. This study therefore obtained strong evidence supporting the hypotheses that C. kelberi caused the fish fauna disassembly and that the predator’s demography was the driver underlying the diversity loss.

Beschreibung: The understanding of the environmental preferences and life history of a species in its native range provides insights for assessing its potential success in a novel area. Hemiodus orthonops is a migratory fish from the Paraguay and Middle Paraná rivers that invaded the Upper Paraná River through a fish pass, constructed in 2002. The invasion of this fish was analyzed based on habitat attributes and its life history in the native range and in the novel habitats. The native and novel habitats presented similar features. The population showed exponential growth in the years following the invasion, with relevant alterations in somatic growth, proportions of items in the diet, and in reproductive investment. The successful invasion appears to be related to similarities in water chemistry and habitat types between the native and novel range and the species' high dispersion ability. The species also showed earlier maturation and use of poor quality, but highly available feeding resources. Comparing life histories there was indication of a trade-off between investment in reproduction and somatic growth, with an increase in the latter in the novel habitats. In addition, the reproductive investment was more associated with offspring survival (oocyte size) than fecundity.

Beschreibung: Several human activities may result in or facilitate species introductions. In aquatic environments, species introductions are often associated with the construction of dams. In this study, we use reservoirs of the Neotropical region as a model to determine the main causes of fish species introductions. We compiled information on non-native fish species present in reservoir ichthyofauna surveys in the past 14 years and classified these species based on their probable reason for introduction (vector). Fish farming activities introduced approximately 7.6-fold more species in reservoirs than the other vectors identified. The matrix of the number of fish species per vectors explained the greatest proportion of the composition of non-native assemblages, whereas the geographic distance and age of the reservoir explained few of these variations. The non-native ichthyofauna composition varied among Neotropical basins and can be explained by the different sets of species introduced by the companies managing the reservoirs. Although power companies have banned stocking with non-natives, fish farming in the Neotropical region continues to use non-native species, and these species are occupying water bodies, especially reservoirs.

Beschreibung: Introduced host species are often characterised by reduced parasite numbers compared to their native populations. Any such advantage gained from parasite release following introduction into a new area may often diminish over a short period as the new host gradually acquires local parasites. In this study, the metazoan parasite communities of four goby species ( Proterorhinus semilunaris , Ponticola kessleri , Neogobius melanostomus , and Neogobius fluviatilis ) recently introduced into the lower River Rhine were investigated. Mean parasite abundance and infracommunity richness were positively associated with time since host introduction, both parasite variables being the highest in P. semilunaris . In Ponticola and Neogobius species, parasite species richness and the dominance of larval parasites in the Lower Rhine were similar to that for non-native populations in the middle Danube. Sporadic local parasite acquisition and infection, predominantly by species commonly found in the native range, led to a relatively high qualitative similarity in parasite communities between hosts. The relationship between parasite abundance and fish size reflected size-dependant food selectivity and/or parasite accumulation throughout the host’s life. Data from this study emphasise the importance of duration of co-occurrence, host habitat and foraging preference, as well as the co-introduction of suitable intermediate hosts, for parasite community composition in related species.

Beschreibung: The introduction and spread of aquatic invasive species constitutes a global epidemic that continues to homogenize the world’s aquatic flora and fauna. Species invasions are occurring at an unprecedented scale, yet few centrally organized distributional databases can accurately display location information used to prioritize management efforts within a watershed, region, or political boundary. For particularly harmful groups of invaders such as some freshwater invertebrates, one consequence is that predictive power is limited because current invasion patterns are unknown. We used the Nonindigenous Aquatic Species database of the US Geological Survey to determine current hotspots of invertebrate invasion in the US and compared those patterns with better-documented fish invasions. Invasive freshwater invertebrates were densely clustered in the Laurentian Great Lakes region compared to invasive fish that were concentrated in Florida and the Southwest. However, temporal patterns of fish and invertebrate invasions did not significantly differ. Ballast water was the most important source of invertebrate introductions, whereas fish were more often introduced by stocking, aquaculture, and aquarium release. A centralized database of current species distributions, ideally at the global scale, would greatly inform prevention and mitigation efforts for harmful species invasions.