ALBERT

Description: The conspicuous retreat of the key species Fucus vesiculosus from the deeper parts of its former distribution area in the Baltic Sea has triggered extensive research on the factors that control its growth. Based on recently obtained knowledge on a large number of potential drivers, we developed a numerical model incorporating effects of abiotic factors on the physiological functions of photosynthesis, respiration, and reproduction and the ecological processes of competition, grazing, and epibiosis. For all input combinations, the model delivers the monthly net growth rate near the bladder wrack’s depth limit and the maximum depth of its vertical distribution. The use of data corresponding to conditions presently observed in the western Baltic Sea sets the year’s maximum algal net growth rate in late spring and 2 minima in early spring and autumn. The depth limit of the wrack’s distribution is set at ~9 m. Light and its absorption by phytoplankton represent by far the most important factors controlling the modeled net growth rate and depth penetration, with the role of epibiosis requiring further investigation. Lacking findings on population dynamics and biotic interactions restrict the generated model to an exploratory rather than a predictive tool.

Description: The impact of seawater acidification on calcifying organisms varies at the species level. If the impact differs between predator and prey in strength and/or sign, trophic interactions may be altered. In the present study, we investigated the impact of 3 different seawater pCO2 levels (650, 1250 and 3500 µatm) on the acid–base status or the growth of 2 predatory species, the common sea star Asterias rubens and the shore crab Carcinus maenas, and tested whether the quantity or size of prey consumed is affected. We exposed both the predators and their prey, the blue mussel Mytilus edulis, over a time span of 10 wk and subsequently performed feeding experiments. Intermediate acidification levels had no significant effect on growth or consumption in either predator species. The highest acidification level reduced feeding and growth rates in sea stars by 56%, while in crabs a 41% decrease in consumption rates of mussels could be demonstrated over the 10 wk experimental period but not in the subsequent shorter feeding assays. Because only a few crabs moulted in the experiment, acidification effects on crab growth could not be investigated. Active extracellular pH compensation by means of bicarbonate accumulation was observed in C. maenas, whereas the coelomic fluid pH in A. rubens remained uncompensated. Acidification did not provoke a measurable shift in prey size preferred by either predator. Mussels exposed to elevated pCO2 were preferred by previously untreated A. rubens but not by C. maenas. The observed effects on species interactions were weak even at the high acidification levels expected in the future in marginal marine habitats such as the Baltic Sea. Our results indicate that when stress effects are similar (and weak) on interacting species, biotic interactions may remain unaffected.

Description: Pseudomonas strains were shown to be regularly associated with the brown macroalga Saccharina latissima from the Baltic Sea, studied over several years, and were identified as producers of the antimicrobially active compound 2,4-diacetylphloroglucinol. These findings support the assumption of a stable association between the Pseudomonas spp. strains and S. latissima in the Baltic Sea. The metabolite profile of the Pseudomonas spp. comprised monoacetylphloroglucinol, 2,4-diacetylphloroglucinol, pyoluteorin and several rhizoxins, which exhibited broad-spectrum antibiotic activities against Gram-positive and Gram-negative bacteria as well as against fungi. Because the antibiotic activities included the inhibition of the 2 algal pathogens Pseudoalteromonas elyakovii and Algicola bacteriolytica, we propose a beneficial effect of these marine pseudomonads on their host S. latissima.

Description: Phytoplankton experience strong and abrupt variations in light intensity. How cells cope with these changes influences their competitiveness in a highly dynamical environment. While a considerable amount of work has focused on photoacclimation, it is still unknown whether processes specific of phytoplankton groups (e.g. calcification and silicification) influence their response to changing light. Here we show that the diatom Phaeodactylum tricornutum and the coccolithophore Emiliania huxleyi respond to an abrupt increase in irradiance by increasing carbon fixation rates, decreasing light absorption through the decrease of light-harvesting pigments and increasing energy dissipation through the xanthophyll cycle. In addition, E. huxleyi rapidly increases calcium carbonate precipitation in response to elevated light intensity, thereby providing an additional sink for excess energy. Differences between the 2 species also emerge with regard to the magnitude and timing of their individual responses. While E. huxleyi show a pronounced decrease in chlorophyll a and fucoxanthin cellular contents following increased light intensity, P. tricornutum has a faster increase in diadinoxanthin quota, a slower decrease in Fv/Fm (ratio of variable to maximum fluorescence) and a stronger increase in organic carbon fixation rate during the first 10 min. Our findings provide further evidence of species-specific responses to abrupt changes in light intensity, which may partly depend on the phytoplankton functional groups, with coccolithophores having a supplementary path (calcification) for the rapid dissipation of excess energy produced after an abrupt increase in light intensity. These differences might influence competition between coexisting species and may therefore have consequences at the community level.

Description: Rising atmospheric CO2 concentrations will have profound effects on atmospheric and hydrographic processes, which will ultimately modify the supply and chemistry of trace metals in the ocean. In addition to an increase in sea surface temperatures, higher CO2 also results in a decrease of seawater pH, known as ocean acidification, with implications for inorganic trace metal chemistry. Furthermore, direct or indirect effects of ocean acidification and ocean warming on marine biota will also affect trace metal biogeochemistry via alteration of biological trace metal uptake rates and metal binding to organic ligands. Currently, we still lack a holistic understanding of the impacts of decreasing seawater pH and rinsing temperatures on different trace metals and marine biota, which complicates projections into the future. Here, we outline how ocean acidification and ocean warming will influence the inputs and cycling of Fe and other biologically relevant trace metals globally, and regionally in high and low latitudes of the future ocean, discuss uncertainties, and highlight essential future research fields.

Description: Three bioassay experiments were performed to study the effects of nutrient and Saharan dust additions on natural diazotrophic communities in the tropical North Atlantic Ocean. Samples for nucleic acid analysis were collected at the beginning and end of 48 h incubations. TaqMan probes specific to 7 diazotrophic phylotypes, viz. filamentous cyanobacteria (Trichodesmium spp.), unicellular cyanobacterial (UCYN) Groups A, B, and C, Gamma A and P Proteobacteria, and Cluster III, were used to quantify nifH DNA abundances. N-2 fixation rates were measured in the same experiments using the N-15(2) gas bubble injection method. N-2 fixation was co-limited by P and Fe. Total nifH abundances increased relative to the control with additions of either Fe or P or both in combination. Additions of dissolved N, alone or in combination with phosphate, induced increases in UCYN-A and Gamma A nifH compared with the control. Saharan dust additions significantly stimulated fixation rates. Abundances of all cyanobacterial and Gamma A nifH phylotypes at least doubled after Saharan dust additions where surface water dissolved Fe concentrations were 〈2 nmol l(-1). Laboratory experiments with cultures of T. erythraeum demonstrated that dust addition promoted colony formation and the persistence of T. erythraeum biomass relative to cultures to which no Fe was added. Our results with both field and laboratory experiments indicate that Saharan dust positively affects diazotrophic phylotype abundances and changes T. erythraeum colony morphology.

Description: Through the use of mesocosm experiments, we show that an unusually early spring phytoplankton bloom can be induced by intermittent high-light periods. We performed mesocosm experiments where plankton assemblages from Kiel Bight (Western Baltic Sea) received a light regime based on the natural seasonal irradiance dimmed to 43% of surface irradiance of cloudless days, starting with irradiance levels of mid-January (6 mesocosms) and mid-February (6 mesocosms). After 6 d, half of the mesocosms received a ca. 2-fold increase in irradiance. In the January mesocosms, a phytoplankton bloom developed only in the treatments with the high-light episode, whereas in the February mesocosms a phytoplankton bloom also developed in the controls. Phytoplankton net growth rates, production:biomass ratios and biomass at the end of the high irradiance episodes were positively correlated to the daily light dose. The relative biomass of diatoms increased with increasing light, whereas the relative biomass of cryptophytes decreased. A bottom-up transmission to mesozooplankton (mainly copepods of the genera Acartia and Oithona) was evident by increased densities of copepod nauplii and egg production under higher light conditions, whereas copepodids and adults showed no responses during the experimental period. The taxonomic composition of the nauplii was shifted to the advantage of Acartia/Centropages (not distinguished at the naupliar stage) under higher light conditions.

Description: In an effort to identify the key mechanisms controlling biological productivity and food web structure in the Chesapeake Bay estuarine turbidity maxima (ETM), we measured plankton community metabolism on a series of surveys in the upper Chesapeake Bay during the winter and spring of 2007 and 2008. Measured quantities included primary production, bacterial production, planktonic community respiration, and algal pigment concentrations. These measurements revealed a classic minimum in photosynthesis in the vicinity of the ETM. Temporal variability in plankton community metabolism, primary production, respiration, and bacterial production, were highest in the southern oligohaline region down-estuary of the ETM, and appeared to be driven by dynamic bio-physical interactions. Elevated primary production and community respiration in this region were often associated with the presence of mixotrophic dinoflagellates. The dinoflagellate contribution to primary production and respiration appeared to be particularly large as a result of their mixotrophic capabilities, which allow them to obtain energy both autotrophically and heterotrophically. This study suggests that mixotrophic dinoflagellates play a key role in pelagic food web in the oligohaline region of Chesapeake Bay supplying most of the labile organic matter during late winter and spring and also providing a vector for transferring microbial production to mesozooplankton.

Description: A model, composed of coupled particle tracking and benthic response modules, for predicting waste solids flux and benthic impacts of gilthead sea bream (Sparus aurata L.) and sea bass (Dicentrarchus labrax L.) aquaculture, was tested at six sites with different hydrodynamics, bathymetries and biomasses in the Aegean and Ionian Seas, Eastern Mediterranean with observations of sediment trap flux and benthic impact indicators. Seven sediment trap validation studies were conducted that varied in design with traps deployed either on the sea bed, attached to nets or in the water column. Model predictions of flux to traps spaced 5 m apart up to 50 m from the cages over a 13 d period were statistically significant (r2 = 0.61, n = 57, p ≤ 0.05). However, the model could not predict adequately the flux to traps spaced 2 m apart in the high-flux zone underneath cages where variability between trap observations was high. In this high-flux zone underneath cages, the averaged model flux predictions resulted in a performance of ± 49%. Statistically significant relationships were established at four sites; between modelled flux and either benthic fauna impact indicator species (S), abundance (A), A/S ratio, Shannon Wiener Index or Biomass Fractionation Index (BFI), (r2 = 0.82, 0.60, 0.57, 0.67 and 0.48, respectively; n = 24, p ≤ 0.05). Two other sites, which did not exhibit an abundance peak in enriched zones, did not fit these relationships. Using relative abundance of taxonomic groups, a modelled flux of 4.1 g m-2 d-1 was a useful boundary; on either side of this boundary, clear trends occurred in pollutant tolerant and intolerant species.

Description: Both ocean warming and acidification have been demonstrated to affect the growth, performance and reproductive success of calcifying invertebrates. However, relatively little is known regarding how such environmental change may affect interspecific interactions. We separately treated green crabs Carcinus maenas and periwinkles Littorina littorea under conditions that mimicked either ambient conditions (control) or warming and acidification, both separately and in combination, for 5 mo. After 5 mo, the predators, prey and predator-prey interactions were screened for changes in response to environmental change. Acidification negatively affected the closer-muscle length of the crusher chela and correspondingly the claw-strength increment in C. maenas. The effects of warming and/or acidification on L. littorea were less consistent but indicated weaker shells in response to acidification. On the community level, however, we found no evidence that predator-prey interactions will change in the future. Further experiments exploring the impacts of warming and acidification on key ecological interactions are needed instead of basing predictions of ecosystem change solely on species-specific responses to environmental change.

Description: Stress often induces metabolically expensive countermeasures. Bivalve shell production is costly and can thus be indirectly impacted by environmental stress. Suboptimal salinity and temperature may constitute stressors that allocate energy away from shell production to cellular processes such as osmoregulation or to the repair of cellular damage. In the course of climate change, water temperatures of the Baltic Sea are predicted to increase, and salinity is predicted to regionally decrease. These shifts may lead to increased stress for temperate marine species adapted to relatively cool water temperatures and high salinity conditions. To better understand the importance of climate change-related stress, we assessed the isolated and interactive effects of salinity and temperature on shell increment (cumulative growth: shell), cellular oxidative stress (accumulation of oxidized lipids and proteins: lipofuscin), instantaneous physiological condition (condition index: CI), and mortality of young Mytilus edulis and Arctica islandica from the western Baltic Sea. Temperature and salinity interactively affected shell increment, lipofuscin accumulation, and mortality of M. edulis as well as shell increment of A. islandica. Shell increment of M. edulis was less affected by hyposalinity than shell increment of A. islandica. In both species the CI decreased and lipofuscin accumulation increased with increasing temperature. Lipofuscin accumulation negatively correlated with shell increment in M. edulis. We conclude that Baltic Sea populations of ecologically relevant bivalve species may experience severe stress by the predicted regional scenario of warming and desalination if evolutionary adaptation does not happen at a similar rate.

Description: Mesopelagic fishes occur in all the world’s oceans, but their abundance and consequently their ecological significance remains uncertain. The current global estimate based on net sampling prior to 1980 suggests a global abundance of one gigatonne (109 t) wet weight. Here we report novel evidence of efficient avoidance of such sampling by the most common myctophid fish in the Northern Atlantic, i.e. Benthosema glaciale. We reason that similar avoidance of nets may explain consistently higher acoustic abundance estimates of mesopelagic fish from different parts of the world’s oceans. It appears that mesopelagic fish abundance may be underestimated by one order of magnitude, suggesting that the role of mesopelagic fish in the oceans might need to be revised.

Description: Seagrasses worldwide are commonly infected by endophytic protists of the genus Labyrinthula. To date, the nature of interaction of endophyte and host is not well understood. In eelgrass (Zostera marina) Labyrinthula zosterae may become virulent (pathogenic) and lead to the loss of entire sea grass beds. One of the best known examples of any marine epidemic were outbreaks of the ´wasting disease´ on both sides of the Atlantic in the 1930s, but smaller infestations have been reported until recently. Up to now, detection of infection by Labyrinthula was based on the wasting index, i.e. the relative area of leaf lesions or microscopy, while genetic data are virtually absent. We characterized a ~1400 base pair portion of the 18S small subunit rDNA in L. zosterae isolates (N=41) from six northern European sites and one southern location (Adriatic Sea) in order to assess identity and potential diversity of endophytic protists. Because there are indications that low salinity impedes Labyrinthula growth, sampling sites included a wide range of salinities from 5-34 psu. A search against the non-redundant GENBANK data base revealed that most isolates are 99% similar to the only L. zosterae 18S sequence available from the data base at all but the Finish site (salinity values 5-7 psu). At the latter site, a different Labyrinthula species occurred, which was also found in fully marine Wadden Sea cultures. A third species was detected in Skagerrak, south-western Baltic and North Sea samples (20-25 psu). We conclude that L. zosterae is widespread among northern European eelgrass sites across wide ranges of salinity.

Description: Growth rates of the cold-water corals (CWC) Madrepora oculata, Lophelia pertusa, Desmophyllum dianthus and Dendrophyllia cornigera were measured over 8 mo under controlled conditions (12°C in the dark, fed 5 times a week) by means of the buoyant weight technique. Additionally, linear growth rates were measured in M. oculata and L. pertusa for 2 and 1 yr, respectively. The weight measurements revealed growth rates, expressed as percent growth per day (mean ± SD), of 0.11 ± 0.04 for M. oculata, 0.02 ± 0.01 for L. pertusa, 0.06 ± 0.03 for D. dianthus and 0.04 ± 0.02 % d–1 for D. cornigera. Growth in M. oculata was significantly higher (p 〈 0.0001) than in the other 3 CWC species. For M. oculata and L. pertusa, also linear growth was recorded. These values (mean ± SD) were 0.014 ± 0.007 and 0.024 ± 0.018 mm d–1 for M. oculata and L. pertusa, respectively. This is the first study that compares the growth rates of 4 different CWC species under the same experimental conditions of water flow, temperature, salinity and food supply. These corals have different growth rates, both in terms of total weight increase and linear increase, and these growth rates can be related to interspecific physiological differences. Data on growth rates are essential to understand the population dynamics of CWC as well as the recovery capacity of these communities after disturbance.

Description: The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early–21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming.

Description: The focus of this study was the 11.55 m long sediment core 303700-7, which was retrieved from the Gdansk Basin during a cruise of RV ‘Poseidon’ within the frame of the Russian–German Project GISEB. The core was analysed for grain size, elemental chemical composition, organic carbon and palynological spectra. The age control was based on palynostratigraphy and 7 radiocarbon datings of bulk sedimentary organic matter. These data provide a high-resolution record of climatic and marine palaeoenvironments in the Gdansk Basin for the last ca. 13 kyr, from the Bølling to late Holocene time. Sedimentation rates were estimated to vary between 0.37 and 1.62 mm yr–1. Major variations in palaeosalinity were estimated from bromine concentrations in the sediment. This method allows the first quantitative reconstruction of palaeosalinity changes in the Baltic Sea, especially profound during the Littorina and Postlittorina periods (middle to late Holocene). In addition, grain size data indicated several Littorina transgressive–regressive stages and a few episodes of increased near-bottom current activity. Our results from the Gdansk Basin are consistent with palaeoceanographic data from other deep basins of the Baltic Sea and provide new insights into the regional Holocene history.

Description: We assessed the effects of light limitation and temperature shift on palatability and induced antiherbivore defense in the brown alga Fucus vesiculosus L. Incubation for 2 wk at light intensities above the compensation point of photosynthesis and in the absence of grazers increased the palatability of F. vesiculosus and its subsequent consumption by the omnivorous isopod Idotea baltica Pallas. This effect correlated with an increased C:N ratio and mannitol content in the algal tissue, presumably due to increased photosynthetic carbon fixation. Mannitol, the primary product of photosynthesis in F. vesiculosus, proved to be a feeding cue for I. baltica, and depletion of the mannitol pool may therefore account for the reduced palatability during light limitation. At light intensities above the compensation point of photosynthesis, F. vesiculosus responded with decreasing palatability when it was exposed to I. baltica grazing. Irrespective of the preceding light regime, such defense induction was prevented during incubation under light limitation. Thus, under low light, defense induction is not only inhibited, but also less necessary due to the relative absence of feeding cues. Upward or downward shifts in water temperature by approximately 10°C also inhibited inducible defense in F. vesiculosus. However, such shifts did not affect algal growth and were therefore the consequence of an impairment of specific defense-related components rather than of resource limitation, unless compensatory growth was given priority over defense.

Description: The synergistic effects of fishing, climate and internal dynamics on population fluctuations are poorly understood due to the complexity of these interactions. In this paper, we combine time series analysis and simulations to investigate the long-term dynamics of an overexploited population in the Mediterranean Sea, and its link with both fishing-induced demographic changes and hydroclimatic variability. We show that the cyclicity of the catch per unit of effort (CPUE) of European hake Merluccius merluccius (EH) vanished in the 1980s, while the correlation between the CPUE and a local environmental index increased. Using simulations, we then show that the cyclicity observed in the EH biomass before the 1980s can have an internal origin, while that its disappearance could be due to the fishing-induced erosion of the age structure. Our results suggest that fishing can trigger a switch from internally generated to externally forced population fluctuations, the latter being characterised by an increasing dependency of the population on recruitment and ultimately on environmental variability. Hydroclimatic modifications occurring in the Mediterranean in the early 1980s could have enhanced these changes by leading to a mismatch between early life stages of EH and favorable environmental conditions. Our conclusions underline the key effect of the interaction between exploitation and climate on the dynamics of EH and its important consequences for management and conservation.

Description: The warming trend for the entire globe (1850 to 2005) is 0.04°C decade–1. A specific warming period started around 1980 and continues until the present. This warming also occurred in the Baltic Sea catchment, which lies between maritime temperate and continental subarctic climate zones. A detailed study of climate variability and the associated impact on the Baltic Sea area for the period 1958 to 2009 revealed that the recent changes in the warming trend are associated with changes in large-scale atmospheric circulation over the North Atlantic. The number and pathways of deep cyclones changed considerably in line with an eastward shift of the North Atlantic Oscillation centers of action. There is a seasonal shift of strong wind events from autumn to winter and early spring. Since the late 1980s, the winter season (DJFM, i.e. December to March) of the Baltic Sea area has tended to be warmer, with less ice coverage and warmer sea surface temperatures, especially pronounced in the northern parts of the Baltic Sea. There is a tendency for increased cloud cover and precipitation in regions that are exposed to westerlies and less cloud coverage at the leeward side of the Scandinavian Mountains and over the Baltic Sea Basin.

Description: We assessed the seasonal change in trophic interactions at the mesograzer and small predator level in a temperate eelgrass system. This was done through stable isotope (δ13C and δ15N) and fatty acid analyses of eelgrass Zostera marina, attached epiphytes, sand microflora, the red alga Delesseria sanguinea, and the 4 most common mesograzer and predator species. Sampling took place monthly in the western part of the Baltic Sea during a whole year (April 2002 to February 2003). The trophic importance of microalgae was corroborated in all studied species. Red algae were consumed to a lesser extent and eelgrass was of minor importance. The degree of dependence on the main carbon sources was species-specific and varied with time. The small gastropod, Rissoa membranacea, mostly grazed epiphytes (73% on average), whereas the fractions of epiphytes and sand microflora showed a more balanced pattern in the other mesograzer species. Stable carbon data and fatty acid composition strongly suggested that epiphytic algae were the primary source of organic matter for mesograzers in late spring and autumn. In summer, sand microflora were of greater importance as carbon sources, except for the amphipod Gammarus oceanicus for which red algae was the most important. Stable nitrogen values indicated that the degree of carnivory was size-dependent in both omnivorous crustacean species studied; larger individuals generally occupied a higher trophic position than did smaller ones. Furthermore, the isopod Idotea baltica was more herbivorous in summer than in the other seasons. Our results confirm the importance of species-specific and temporal variability for the effect of mesograzers in eelgrass systems. The significance of mesograzers as determinants of food-web structure via the reduction of epiphytes is further corroborated by our study, and the observed high plasticity of mesograzers concerning food sources may promote the stability of eelgrass food webs despite strong seasonal variations in the biomass of primary producers.

Description: Culturing experiments were performed with the benthic foraminifer Ammonia aomoriensis from Flensburg Fjord, western Baltic Sea. The experiments simulated a projected rise in atmospheric CO2 concentrations. We exposed specimens to 5 seawater pCO2 levels ranging from 618 µatm (pH 7.9) to 3130 µatm (pH 7.2) for 6 wk. Growth rates and mortality differed significantly among pCO2 treatments. The highest increase of mean test diameter (19%) was observed at 618 µatm. At partial pressures 〉1829 µatm, the mean test diameter was observed to decrease, by up to 22% at 3130 µatm. At pCO2 levels of 618 and 751 µatm, A. aomoriensis tests were found intact after the experiment. The outer chambers of specimens incubated at 929 and 1829 µatm were severely damaged by corrosion. Visual inspection of specimens incubated at 3130 µatm revealed wall dissolution of all outer chambers, only their inner organic lining stayed intact. Our results demonstrate that pCO2 values of ≥929 µatm in Baltic Sea waters cause reduced growth of A. aomoriensis and lead to shell dissolution. The bottom waters in Flensburg Fjord and adjacent areas regularly experience pCO2 levels in this range during summer and fall. Increasing atmospheric CO2 concentrations are likely to extend and intensify these periods of undersaturation. This may eventually slow down calcification in A. aomoriensis to the extent that net carbonate precipitation terminates. The possible disappearance of this species from the Baltic Sea and other areas prone to seasonal undersaturation would likely cause significant shifts in shallow-water benthic ecosystems in the near future.

Description: Climate models predict increases in frequency of summer heat waves. In Europe, such events have already caused declines in seagrass meadows, highlighting the importance of short-term responses of local communities to climate stress. Understanding the variability among populations along the European thermal gradient in response to heat waves is crucial for seagrass conservation and management. Using a mesocosm we compared effects of a simulated heat wave on the photophysiology of Zostera marina populations coming from low (43° N, Adriatic Sea) and high latitudes (56° N, North and Baltic Seas). Measurements before, during and up to 4 wk after the heat wave included photophysiological parameters derived from light response curves generated by PAM fluorometry and gene expression using qRT-PCR. In all 3 populations, initial exposures to thermal stress were characterized by increases in dark adapted effective quantum yield (Y0), maximum electron transfer rate of PSII (ETRmax) and slope of the light response curve (α), coinciding with upregulations of the gene superoxidase dismutase [Mn]. With continuation of the heat wave these initial effects disappeared, demonstrated by declines in Y0, ETRmax and α relative to controls. Z. marina from the Adriatic suffered from the simulated heat wave as much as its high-latitude counterparts. However, we also demonstrate slight photophysiological differences between the populations during the recovery phase, where performance of high-latitude populations continued declining even after water temperatures returned to control levels, while photochemical activity fully recovered in the Adriatic population. These results might draw the attention of future studies and seagrass conservation efforts.

Description: Kessler et al. (Reports, 21 January 2011, p. 312) reported that methane released from the 2010 Deepwater Horizon blowout, approximately 40% of the total hydrocarbon discharge, was consumed quantitatively by methanotrophic bacteria in Gulf of Mexico deep waters over a 4-month period. We find the evidence explicitly linking observed oxygen anomalies to methane consumption ambiguous and extension of these observations to hydrate-derived methane climate forcing premature.

Description: At 2 modern deep-water cold-seep sites, the North Alex Mud Volcano (eastern Mediterranean Sea, water depth ~500 m) and the Concepción Methane Seep Area (south-east Pacific Ocean, water depth ~700 m), we found abundant catshark (Chondrichthyes: Scylio - rhinidae) and skate (Chondrichthyes: Rajidae) egg capsules, respectively, associated with carbonates and tubeworms. Fossilized catshark egg capsules were found at the 35 million year old Bear River Cold-Seep Deposit (Washington State, USA) closely associated with remains of tubeworms and sponges. We suggest that cold-seep ecosystems have served as nurseries for predatory elasmobranch fishes since at least late Eocene time and therewith possibly play an important role for the functioning of deep-water ecosystems.

Description: In 1956, the shallow-water grouper Cephalopholis argus was introduced from Moorea (French Polynesia), where grouper diversity (14 species) is high, to the Main Hawaiian Islands (MHI), where only 2 rare native deep-water groupers occur. In this non-native environment, the species has flourished and has become the dominant apex predator on many reefs. In the present study, a comparison of non-native populations of C. argus in the MHI with native populations in Moorea showed that mean total length (32.0 vs. 26.9 cm), mass (722 vs. 326 g), growth, and body condition were each significantly elevated in the MHI. In addition, while an ontogenetic shift towards larger prey occurred in both locations, it was faster and more consistent in Moorea than in the MHI. As a result, while small C. argus of comparable size in the 2 locations consumed similar-sized prey, large C. argus in Moorea consumed significantly longer and deeper-bodied prey than their counterparts in the MHI. This pattern was unrelated to the size distributions of available prey and may thus reflect stronger intra- and interspecific competition for small prey in Moorea. Although ecological release in a broader sense (i.e. a combination of predator release, parasite release, and competitive release) may play a role, the most direct explanation for the observed differences between C. argus in native habitats in Moorea (with many competing grouper species) and non-native habitats in the MHI (few competitors) would be competitive release (here used in the sense of benefits resulting from the reduction of interspecific competition).

Description: We analysed carbon (δ13C) and nitrogen (δ15N) isotope ratios of organisms and biogenic tissues from Comau Fjord (southern Chile) to characterise benthic food webs and spatial isotope variability in this ecosystem. These values were intended to serve as a baseline for detecting anthropogenic impacts on Patagonian marine fjord ecosystems in later studies. Benthic macro algae and invertebrate suspension feeders were primarily considered, with some supplementary data from cyanobacteria, plankton, fish, and coastal vertebrates. Six depth transects typified the lateral salinity gradients from the innermost part of the fjord to its mouth, as well as the vertical density gradients caused by freshwater inflow. Carbon isotope signatures indicated predominant consumption of either CO2 or HCO3– for benthic macroalgal. All CO2 users belonged to rhodophytes. The δ15N values of benthic macrophytes decreased with decreasing salinity, both vertically and along the fjord axis. This implies the influence of 15N-poor terrestrial dissolved inorganic nitrogen (DIN) at these sites. Enhanced influence of freshwater influx also lowered N contents and increased C/N ratios in algal tissues. Exceptionally high macroalgae δ15N values at the seabird and sealion colony Isla Liliguapi point to animal faeces as an additional source of 15N-enriched DIN. Thus, DIN sources not originating from the open sea are additionally utilised by the benthic macroalgae in the fjord. In contrast, mussel tissue from the same locations was much less influenced by varying DIN sources. Among benthic suspension feeders, mytilids (Mytilus chilensis, Aulacomya ater) had the lowest and scleractinian corals (Desmophyllum dianthus) had the highest δ15N values, and Balanidae (Elminius kingii) and gorgonians (Primnoella sp.) showed values in between. The preference for specific size classes of marine particulate organic matter (seston) as food serves as an explanation for the δ15N variability observed between the different benthic suspension feeders.

Description: The cod Gadus morhua stock in the eastern Baltic Sea has seen a recent miraculous recovery, mainly due to a drastic decrease in fishing mortality (F). Here we explore 3 options for rebuilding the stock to the size (biomass that can produce the maximum sustainable yield, or Bmsy) that is required by international law and that can support high long-term yields. The first option implements a fishing mortality of F = 0.3, as is aimed for under the current European Commission management plan. The second option implements in addition the current constraint of a maximum annual increase of 15% in total allowable catches until a catch corresponding to F = 0.3 is reached. The third option freezes the 2010 catch for 2 yr before allowing a linear increase with spawning stock biomass towards 90% of the maximum sustainable yield. We show that the first option provides the highest catches for the first 3 yr, but fails to rebuild the biomass to the level of Bmsy. The second option rebuilds the biomass above Bmsy only temporarily and results in the lowest catches over a 10 yr period. The third option rebuilds the biomass above Bmsy and provides high catches and the highest profit within 10 yr. Within a decade, all 3 options provide several-fold higher biomasses, catches, and profits compared to the current situation, underlining the benefits that can be obtained from proper fisheries management. In comparison, the so-called precautionary management approach (F = 0.6) implemented until 2006 would perform worse in every respect.

Description: Rising atmospheric CO2 concentrations could cause a calcium carbonate subsaturation of Arctic surface waters in the next 20 yr, making these waters corrosive for calcareous organisms. It is presently unknown what effects this will have on Arctic calcifying organisms and the ecosystems of which they are integral components. So far, acidification effects on crustose coralline red algae (CCA) have only been studied in tropical and Mediterranean species. In this work, we investigated calcification rates of the CCA Lithothamnion glaciale collected in northwest Svalbard in laboratory experiments under future atmospheric CO2 concentrations. The algae were exposed to simulated Arctic summer and winter light conditions in 2 separate experiments at optimum growth temperatures. We found a significant negative effect of increased CO2 levels on the net calcification rates of L. glaciale in both experiments. Annual mean net dissolution of L. glaciale was estimated to start at an aragonite saturation state between 1.1 and 0.9 which is projected to occur in parts of the Arctic surface ocean between 2030 and 2050 if emissions follow ‘business as usual’ scenarios (SRES A2; IPCC 2007). The massive skeleton of CCA, which consist of more than 80% calcium carbonate, is considered crucial to withstanding natural stresses such as water movement, overgrowth or grazing. The observed strong negative response of this Arctic CCA to increased CO2 levels suggests severe threats of the projected ocean acidification for an important habitat provider in the Arctic coastal ocean.

Description: As part of the PeECE II mesocosm project, we investigated the effects of pCO2 levels on the initial step of heterotrophic carbon cycling in the surface ocean. The activities of microbial extracellular enzymes hydrolyzing 4 polysaccharides were measured during the development of a natural phytoplankton bloom under pCO2 conditions representing glacial (190 µatm) and future (750 µatm) atmospheric pCO2. We observed that (1) chondroitin hydrolysis was variable throughout the pre-, early- and late-bloom phases, (2) fucoidanase activity was measurable only in the glacial mesocosm as the bloom developed, (3) laminarinase activity was low and constant, and (4) xylanase activity declined as the bloom progressed. Concurrent measurements of microbial community composition, using denaturing-gradient gel electrophoresis (DGGE), showed that the 2 mesocosms diverged temporally, and from one another, especially in the late-bloom phase. Enzyme activities correlated with bloom phase and pCO2, suggesting functional as well as compositional changes in microbial communities in the different pCO2 environments. These changes, however, may be a response to temporal changes in the development of phytoplankton communities that differed with the pCO2 environment. We hypothesize that the phytoplankton communities produced dissolved organic carbon (DOC) differing in composition, a hypothesis supported by changing amino acid composition of the DOC, and that enzyme activities responded to changes in substrates. Enzyme activities observed under different pCO2 conditions likely reflect both genetic and population-level responses to changes occurring among multiple components of the microbial loop.

Description: Mucus, a complex composed primarily of carbohydrates, is released in similar quantities by scleractinian warm- and cold-water reef corals, and can function as an important carrier of organic material from corals to a range of consumers, microbes in particular. However, information about mucus chemical composition is rare for warm-water corals and non-existent for cold-water corals. This study therefore presents comparative carbohydrate composition analyses of mucus released by the dominant and cosmopolitan warm- and cold-water coral genera. Arabinose was the major mucus carbohydrate component for the genus Acropora, but was not found in cold-water coral mucus. Mucus derived from corals of the genus Fungia contained significantly more fucose than the mucus of all other coral genera. However, comparison of mucus carbohydrate composition for the warm- and cold-water corals in the present study and in the literature revealed no significant differences. This indicates use of similar carbohydrate components (with the exception of arabinose) during mucus synthesis by scleractinian corals, largely irrespective of zooxanthellate or azooxanthellate carbon supply mechanisms.

Description: Previous studies have suggested that phytoplankton play an important role in the biogeochemical cycling of iodine, due to the appearance of iodide in the euphotic zone. Changes in the speciation of iodine over the course of the growth cycle were examined in culture media for a variety of phytoplankton taxa (diatoms, dinoflagellates and prymnesiophytes). All species tested showed the apparent ability to reduce iodate to iodide, though production rates varied considerably between species (0.01 to 0.26 nmol l–1 µg–1 chl a d–1), with Eucampia antarctica the least and Pseudo-nitzschia turgiduloides the most efficient iodide producers. Production was found to be species specific and was not related to biomass (indicated by e.g. cell size, cell volume, or chl a content). In all species, except for the mixotrophic dinoflagellate Scrippsiella trochoidea, iodide production commenced in the stationary growth phase and peaked in the senescent phase of the algae, indicating that iodide production is connected to cell senescence. This suggests that iodate reduction results from increased cell permeability, which we hypothesize is due to subsequent reactions of iodate with reduced sulphur species exuded from the cell. A shift from senescence back to the exponential growth phase resulted in a decline in iodide and indicated that phytoplankton-mediated oxidation of iodide to iodate was likely to be occurring. Iodide production could not be observed in healthy cells kept in the dark for short periods. Bacterial processes appeared to play only a minor role in the reduction of iodate to iodide.

Description: Traditionally, consumer–prey interactions have been considered as purely negative, but herbivores may have positive effects on plants and their productivity. Grazing may enhance prey biomass-specific productivity by directly or indirectly reducing the competition for light, nutrients, and space. We studied the effect of 4 common mesograzers, the isopod Idotea baltica, the amphipod Gammarus oceanicus, and the gastropods Littorina littorea and Rissoa membranacea on epiphytes in an eelgrass Zostera marina L. system. Eelgrass was grown in laboratory mesocosms for a set of experiments manipulating mesograzer species identity, mesograzer density and nutrient concentration. We measured epiphyte biomass-specific productivity via incorporation of radioactive carbon. Herbivore effects on epiphyte photosynthetic capacity were strongly positive for R. membranacea, moderately positive for L. littorea and I. baltica and zero for G. oceanicus under low nutrient supply. Both gastropods increased the nitrogen content of epiphytes, especially the small R. membranacea, and enhanced epiphyte growth. The crustacean species did not increase epiphyte nutrient content, but I. baltica probably enhanced epiphyte productivity by removing the overstory of algal cells, and thus reducing competition for light, nutrients, and space. The positive effect of the 2 gastropod species disappeared under higher nutrient supply, implying the importance of nutrient limitation for this interaction. The positive effect of I. baltica remained at moderate grazer densities despite the higher nutrient concentrations.

Description: Previous studies on trait-mediated trophic interactions in marine ecosystems were restricted to pair-wise interactions between one species of meso-herbivore and plant, though multi-grazer interactions are more common in nature. We investigated whether the feeding of one consumer, either the periwinkle Littorina littorea or the isopod Idotea baltica, affected consumption by the other consumer via anti-herbivory defence induction in the brown seaweed Fucus vesiculosus. To test the generality of our findings, we ran similar experiments with seaweed/grazer populations in the North and Baltic Seas (NE Atlantic). Grazer-specificity in induction strength was assessed by using the same species of grazer for induction and consumption. ‘Indirect’ induction effects were assessed by using different species of grazers for induction and consumption. Palatability assays were run with live algae and with reconstituted food to distinguish between different mechanisms of resistance. Grazing by herbivores induced a chemical defence in F. vesiculosus. In the North Sea population, the induced defences were only effective against I. baltica, regardless of inducer identity. The sensitive responses of I. baltica to the induced defences were also detected in the reconstituted food assays using Baltic Sea organisms. Thus, marine meso-grazers may be affected by previous feeding through the same or a different species of consumer by modified prey traits, such as induced chemical defences. Furthermore, the magnitude of the effect in the induced defences can be determined by species-specific sensitivity.

Description: How multiple stressors influence fish stock dynamics is a crucial question in ecology in general and in fisheries science in particular. Using time-series covering a 30 yr period, we show that the body growth of the central Baltic Sea herring Clupea harengus, both in terms of condition and weight-at-age (WAA), has shifted from being mainly driven by hydro-climatic forces to an inter-specific density-dependent control. The shift in the mechanisms of regulation of herring growth is triggered by the abundance of sprat, the main food competitor for herring. Abundances of sprat above the threshold of ~18 × 1010 ind. decouple herring growth from hydro-climatic factors (i.e. salinity), and become the main driver of herring growth variations. At high sprat densities, herring growth is considerably lower than at low sprat levels, regardless of the salinity conditions, indicative of hysteresis in the response of herring growth to salinity changes. The threshold dynamic accurately explains the changes in herring growth during the past 3 decades and in turn contributes to elucidate the parallel drastic drop in herring spawning stock biomass. Studying the interplay between different stressors can provide fundamental information for the management of exploited resources. The management of the central Baltic herring stock should be adaptive and take into consideration the dual response of herring growth to hydro-climatic forces and food-web structure for a sound ecosystem approach to fisheries.

Description: Biological dinitrogen (N2) fixation is the primary input of fixed nitrogen (N) into the marine biosphere, making it an essential process contributing to the biological functions of all organisms. Because biologically available N often limits marine productivity, microbial processes leading to its loss and gain (e.g. denitrification and N2 fixation, respectively) play an important role in global biogeochemical cycles. Bioturbation is known to influence benthic N cycling, most often reported as enhancement of denitrification and a subsequent loss of N2 from the system. N2 fixation has rarely been addressed in bioturbation studies. Instead, sedimentary N2 fixation typically has been considered important in relatively rare, localized habitats such as rhizosphere and phototrophic microbial mat environments. However, the potential for N2 fixation in marine sediments may be more widespread. We show here that nitrogenase activity can be very high (up to 5 nmol C2H4 cm–3 h–1) in coastal sediments bioturbated by the ghost shrimp Neotrypaea californiensis and at depths below 5 cm. Integrated subsurface N2-fixation rates were greater than those previously found for un-vegetated estuarine sediments and were comparable to rates from photosynthetic microbial mats and rhizospheres. Inhibition experiments and genetic analysis showed that this activity was mainly linked to sulfate reduction. Sulfate-reducing bacteria (SRB) are widespread and abundant in marine sediments, with many possessing the genetic capacity to fix N2. Our results show that N2 fixation by SRB in bioturbated sediments may be an important process leading to new N input into marine sediments. Given the ubiquity of bioturbation and of SRB in marine sediments, this overlooked benthic N2 fixation may play an important role in marine N and carbon (C) cycles.

Description: We examined the simultaneous effect of climate warming and light availability on the phytoplankton spring bloom using 1400 l (1 m depth) indoor mesocosms. The timing of the spring bloom was advanced both by warming and higher light intensity, but the influence of temperature on the phytoplankton community was stronger than the light effect. Warming affected phytoplankton directly and indirectly via enhanced grazing pressure at higher temperatures. Warming resulted in markedly lower phytoplankton biomass and a shift towards smaller cell sizes. It also led to changes in the community structure of phytoplankton and zooplankton. Among phytoplankton, large-celled diatoms were most negatively affected by warming. Overwintering zooplankton species (Oithona, Pseudocalanus) remained dominant in the cold treatments, while they were replaced by late spring or summer species (Acartia, Centropages, Temora) in the warmed treatments. Our results show that understanding food web interactions might be very important to the study of the effects of climate warming on pelagic ecosystems.

Description: Biological dinitrogen (N2) fixation is the primary input of fixed nitrogen (N) into the marine biosphere, making it an essential process contributing to the biological functions of all organisms. Because biologically available N often limits marine productivity, microbial processes leading to its loss and gain (e.g. denitrification and N2 fixation, respectively) play an important role in global biogeochemical cycles. Bioturbation is known to influence benthic N cycling, most often reported as enhancement of denitrification and a subsequent loss of N2 from the system. N2 fixation has rarely been addressed in bioturbation studies. Instead, sedimentary N2 fixation typically has been considered important in relatively rare, localized habitats such as rhizosphere and phototrophic microbial mat environments. However, the potential for N2 fixation in marine sediments may be more widespread. We show here that nitrogenase activity can be very high (up to 5 nmol C2H4 cm–3 h–1) in coastal sediments bioturbated by the ghost shrimp Neotrypaea californiensis and at depths below 5 cm. Integrated subsurface N2-fixation rates were greater than those previously found for un-vegetated estuarine sediments and were comparable to rates from photosynthetic microbial mats and rhizospheres. Inhibition experiments and genetic analysis showed that this activity was mainly linked to sulfate reduction. Sulfatereducing bacteria (SRB) are widespread and abundant in marine sediments, with many possessing the genetic capacity to fix N2. Our results show that N2 fixation by SRB in bioturbated sediments may be an important process leading to new N input into marine sediments. Given the ubiquity of bioturbation and of SRB in marine sediments, this overlooked benthic N2 fixation may play an important role in marine N and carbon (C) cycles.

Description: We examined the RNA and DNA concentration of field-caught scallops Chlamys islandica, maintained in suspended cultures at 15 and 30 m depth, and scallops from a wild population at 50 to 60 m in Kobbefjord, southwest Greenland. General relations between RNA and DNA concentrations and individual shell height were established, and we found that the RNA:DNA ratio (RD) worked well as a standardisation of the RNA concentration independent of size and sex. During an experimental period of 14 mo, we observed a pronounced seasonal pattern in RD and mass growth, and differences between depths. Even though the period with high levels of RD reflected the growth season relatively well, RD was a poor predictor of individual mass growth rates of C. islandica. However, we found a non-linear response in RD to increased food concentrations resulting in RD being up- and down-regulated at the beginning and end of the productive summer season, respectively. These results indicate that short-term dynamics in the actual mass growth rate might be controlled through regulation of ribosome activity rather than ribosome number (RNA concentration). This adaption would allow scallops to up-regulate protein synthesis more rapidly, thereby ensuring efficient utilisation of the intense peaks in food availability in coastal areas in the Arctic. Therefore, we suggest that RD in C. islandica reflects the growth potential rather than the actual growth rate. Still, the amount of unexplained variance in RD is considerable and not independent over time, suggesting the existence of unresolved mechanisms or relationships.

Description: Recent studies in the marine environment have suggested that the limited phenotypic plasticity of cold-adapted species like Atlantic cod (Gadus morhua L.) will cause distributions to shift toward the poles in response to rising sea temperatures. Some cod stocks are predicted to collapse, but this remains speculative because almost no information is available on the thermal tolerance of cod in its natural environment. We used electronic tags to measure the thermal experience of 384 adult Atlantic cod from eight different stocks found in the NE Atlantic. Over 100,000 days of data were collected in total. The data demonstrate that cod is an adaptable and tolerant species capable of surviving and growing in a wide range of temperate marine climates. Total thermal niche ranged from -1.5°C to 19°C; this range was narrower (1°C to 8°C) during the spawning season. Cod in each of the stocks studied had a thermal niche of approximately 12°C, but latitudinal differences in water temperature meant that cod in the warmer, southern regions experienced three times the degree days (~4000 DD year-1) than individuals from northern regions (~1200 DD year-1). Growth rates increased with temperature, reaching a maximum in those cod with a mean thermal history of between 8°C and 10°C. Our direct observations of habitat occupation suggest that adult cod will be able to tolerate warming seas but that cod populations may still be affected because the effects of marine climate change will impact cod at earlier life-history stages or via indirect effects on prey species.

Description: Photoacclimation models are a prerequisite for accurate estimates of primary production in aquatic environments under typically variable light conditions. They generally start from empirical functions of the internal chlorophyll a (chl a) or nutrient quota (e.g. the Droop model). We propose that physiological variations in phytoplankton reflect phenotypic adaptation which maximizes the growth rate. Growth maximization has to account for indirect effects of the enhancement of carbon (C) acquisition by acclimation, primarily through concomitant changes in the intracellular nitrogen (N) budget. Our model expresses, for the first time, the indirect effect of alterations in N uptake on C assimilation by a parameter-free trade-off between the 2 uptake functions. The model explicitly prescribes optimal protein partitioning between N and C uptake and sub-partitioning into carboxylation (1,5-bisphosphate carboxylase/oxygenase, Rubisco) and light harvesting. Applications to various published experimental data for different phytoplankton species support the validity of the optimality hypothesis and point to different flexibility in the re-organization of chloroplasts between taxa as well as to different time-scales on which photoacclimation operates. Simulations of a batch culture with the haptophyte Isochrysis galbana show that a decoupling in pigment N:C from cellular N:C may explain observed lag phases in chl a:C regulation. For diatoms, seemingly stronger constraints in intra-cellular stoichiometry determine the photoacclimative response to variable light regimes, as simulated and reported for Skeletonema costatum. N and chl a quotas correlate well in nutrient-limited chemostats of Thalassiosira fluviatilis, but in part decouple under light limitation. In N limited growth, non-linearity in N:C as expressed by the Droop function results from a combination of a linear quota dependency, down-regulation of relative carboxylation capacity, and increasing N costs of chl a synthesis at elevated growth rates. Our optimality assumption that includes indirect feed-backs through the concept of protein partitioning generates an accurate model for adaptation in physiological traits.

Description: Zooplankton feeding formulations in plankton models have exclusively focused on the relation between food concentration and ingestion, with respiration and excretion being treated separately, despite experimental evidence for strong links among these processes. We present an optimal current-feeding model linking ingestion, respiration, and assimilation efficiency to foraging activity. The Ivlev model is a special case of our optimal current-feeding model, which applies to static feeding behaviour. We validate our model with experimental data for copepods, ciliates, and dinoflagellates. Parameter estimates suggest that phylogenetic grouping is more important than predator size in determining feeding behaviour. Respiratory costs of foraging, e.g. for generating a feeding current, may be much larger than previously thought, are larger in smaller organisms, and might explain the independent development of feeding thresholds in different micro- and mesozooplankton groups. Both preferential feeding on, and lower feeding thresholds for, larger food particles are predicted to derive from greater capture efficiency owing to enhanced detectability of larger particles. The relation between feeding threshold and prey size appears to depend on feeding strategy but not on predator size, as a common relationship seems to apply for current feeders (ciliates and copepods) spanning a vast size range. Our model exhibits an inverse relationship between ingestion and assimilation efficiency, reducing the contribution of copepods to export of organic matter relative to remineralisation at low food concentrations. Export ratio variations previously thought to require strong shifts in community composition can be generated by changes in feeding behaviour predicted by our model.

Description: The impact of moderate environmental stress may be modulated by stress-induced shifts of biotic interactions such as host – epibiont relationships. We studied the stress regime in shallow Western Baltic habitats, the variability of fouling at different temporal and spatial scales, and whether common stressors - low light, high temperature, grazing – affect the abundance and composition of the biofilm on a regionally important macroalga, the bladder wrack Fucus vesiculosus. We further explore the alga’s capacity to chemically modulate the recruitment of microfoulers and whether this ability is impacted by stress. In laboratory, mesocosm and field experiments fouling pressure and epibiotic cover on the algae varied strongly with changing environmental conditions such as temperature, irradiance, depth or grazing. The expectation that abiotic stress affects the fouling-modulating ability of the alga and, thus, indirectly produces the observed variability of epibiosis was not generally confirmed. Indeed, while the strength of chemical antifouling resistance varied seasonally, with a maximum in winter/spring and a minimum in late summer, this could not be related to temporal patterns of environmental stress, fouling pressure, or growth of Fucus. Only the seasonal variation in reproduction seemed to be in phase with antifouling activity. Controlled experiments confirmed that resistance strength was not affected by temperature or grazing, and only moderately by light. We conclude that the fouling modulation ability of Fucus vesiculosus may suffer from light-reduction (e.g. by eutrophication effects) while they are not sensitive to the predicted warming or enhanced grazing.

Description: We review research from the last 40 yr on macroalgal–bacterial interactions. Marine macroalgae have been challenged throughout their evolution by microorganisms and have developed in a world of microbes. Therefore, it is not surprising that a complex array of interactions has evolved between macroalgae and bacteria which basically depends on chemical interactions of various kinds. Bacteria specifically associate with particular macroalgal species and even to certain parts of the algal body. Although the mechanisms of this specificity have not yet been fully elucidated, ecological functions have been demonstrated for some of the associations. Though some of the chemical response mechanisms can be clearly attributed to either the alga or to its epibiont, in many cases the producers as well as the mechanisms triggering the biosynthesis of the biologically active compounds remain ambiguous. Positive macroalgal–bacterial interactions include phytohormone production, morphogenesis of macroalgae triggered by bacterial products, specific antibiotic activities affecting epibionts and elicitation of oxidative burst mechanisms. Some bacteria are able to prevent biofouling or pathogen invasion, or extend the defense mechanisms of the macroalgae itself. Deleterious macroalgal–bacterial interactions induce or generate algal diseases. To inhibit settlement, growth and biofilm formation by bacteria, macroalgae influence bacterial metabolism and quorum sensing, and produce antibiotic compounds. There is a strong need to investigate the bacterial communities living on different coexisting macroalgae using new technologies, but also to investigate the production, localization and secretion of the biological active metabolites involved in those possible ecological interactions.

Description: The vertical distribution of methane- and ammonia-oxidizing bacteria (MOB and AOB, respectively), and the physicochemical conditions in the chemocline of Lake Kinneret (Israel) were studied at a resolution of 10 cm from 16.2 to 17.7 m depth. Profiles of the chemical parameters indicated decreasing concentrations of methane (from 22.4 to 0.11 µmol l–1) and ammonia (from 14.2 to 8.4 µmol l–1) towards the water surface and in close proximity to the chemocline. The disappearance of methane coincided with methane oxidation that could be corroborated throughout this layer with highest rates at 17.4 to 17.6 m. Disappearance of ammonia could not be linked to ammonia oxidation exclusively. The genes pmoA and the homologous amoA (coding for subunit α of the methane and ammonia monooxygenase, respectively) were amplified by PCR. The products were analyzed by terminal restriction fragment length polymorphism (T-RFLP) and sequencing of clone libraries. The results demonstrated that different MOB and AOB communities are established along the concentration gradient within the narrow layer of the metalimnetic chemocline. Changes in the intensity of the T-RFLP peaks and the frequency of different groups of alpha- and gammaproteobacterial MOB, and betaproteobacterial AOB, coincided with the concentration gradients of methane, ammonia, nitrate, and oxygen in the chemocline. This suggests that different communities of MOB, and to a lesser extent AOB, contribute to the formation of chemical gradients of their particular substrates in the chemocline

Description: Effects of elevated temperature on the formation and subsequent degradation of diatom aggregates were studied in a laboratory experiment with a natural plankton community from the Kiel Fjord (Baltic Sea). Aggregates were derived from diatom blooms that developed in indoor mesocosms at 2.5 and 8.5 degrees C, corresponding to the 1993 to 2002 mean winter in situ temperature of the Western Baltic Sea and the projected sea surface temperature during winter in 2100, respectively. Formation and degradation of diatom aggregates at these 2 temperatures in the dark were promoted with roller tanks over a period of 11 d. Comparison of the 2 temperature settings revealed an enhanced aggregation potential of diatom cells at elevated temperature, which was likely induced by an increased concentration of transparent exopolymer particles (TEP). The enhanced aggregation potential led to a significantly higher proportion of particulate organic matter in aggregates at 8.5 degrees C. Moreover, the elevated temperature favoured the growth of bacteria, bacterial biomass production, and the activities of sugar- and protein-degrading extracellular enzymes in aggregates. Stimulating effects of rising temperature on growth and metabolism of the bacterial community resulted in an earlier onset of aggregate degradation and silica dissolution. Remineralization of carbon in aggregates at elevated temperature was partially compensated by the formation of carbon-rich TEP during dark incubation. Hence, our results suggest that increasing temperature will affect both formation and degradation of diatom aggregates. We conclude that the vertical export of organic matter through aggregates may change in the future, depending on the magnitude and vertical depth penetration of warming in the ocean.

Description: Models of multiple potentially limiting nutrients currently employ either multiplicative or threshold formulations, neither of which has a sound mechanistic explanation. Despite experimental evidence that lack of P severely constrains N assimilation, this mechanism has not been considered for constructing models of multi-nutrient limitation. We construct a phytoplankton optimal growth model linking C, chlorophyll (Chl), N, and P through a limitation chain in which P limits N assimilation, N limits photosynthesis and photosynthesis limits growth. The resulting formulation possesses characteristics of both multiplicative and threshold approaches and provides a mechanistic foundation for modelling multi-nutrient and light limitation of phytoplankton growth. The model compares well with experimental observations for a variety of unicellular phytoplankton species. It is suggested that the widely held view that N and P limitation act independently of each other is based on an invalid interpretation of experimental observations and that the transition from N to P limitation occurs over a wide range of colimitation rather than a sharply-defined transition point. If the species considered in this study are representative for marine phytoplankton, our model results indicate that most phytoplankton are colimited by N and P when inorganic N and P are simultaneously exhausted in the surface ocean. The model suggests that the close match between marine inorganic (Redfield) and phytoplankton N:P ratios results from optimal nutrient utilisation but does not indicate optimality of Redfield N:P.

Description: Generalist and opportunistic marine predators use flexible foraging behaviour to exploit prey bases that change in diversity and spatial and temporal distributions, Behavioural flexibility is constrained by characteristics Such as individual cognitive and physical capabilities, age, reproductive condition and central place foraging. To assess flexibility in the foraging tactics of a marine bird, we investigated the diets and foraging behaviour of the largest seabird predator in the North Atlantic Ocean. Northern gannets Sula bassana exploit abroad spectrum of pelagic prey that range in mass by more than 2 orders of magnitude, We investigated their foraging activity at their largest. offshore colony in the western Atlantic Ocean during 1998 to 2002, when they preyed primarily on shoals of spawning and post-spawning capelin Mallotus villosus, a small forage fish (similar to 15 g), and also on a much larger pelagic fish, post-smolt Atlantic salmon Salmo salar (similar to 200 g). Inter-annual dietary variation is associated with gannet and prey fish distributions. Landings of capelin at the colony by gannets were correlated with returns of larger foraging flocks from inshore, whereas landings of Atlantic salmon were associated with smaller flocks returning from offshore. Maximum foraging trip distances ranged from 20 to 200 km and averaged 57 +/- 12 (SE) km, consistent with distances to inshore capelin aggregations. When capelin abundance was low (in 2002), more gannets foraged offshore, preyed on large pelagic fishes (mostly Atlantic salmon) and exhibited the greatest dietary diversity. Though the Outbound portions of foraging trips were more sinuous than inbound routes, individual gannets exhibited general fidelity to foraging sites. These large avian predators used flexible foraging tactics to adjust to changing prey conditions and generate longer-term strategies to Lake advantage of diverse trophic interactions over a range of ocean ecosystems.

Description: Individual migratory schedules and wintering areas of northern gannets Morus bassanus were studied over 2 consecutive winters by deploying geolocation data loggers on breeding adults from the Bass Rock, UK. Northern gannets attended the breeding colony on Bass Rock until between 24 September and 16 October (median: 5 October). Afterwards, individual birds engaged in different migratory behaviour. Of the 22 birds tracked until at least December, 18% wintered in the North Sea and the English Channel, 27% in the Bay of Biscay and the Celtic Sea, 9% in the Mediterranean Sea and 45% off West Africa. Individual winter home ranges as measured by the 75% kernel density contours varied between 8 100 and 308 500 km(2) (mean = 134 000 km(2)). Several northern gannets migrated northwards from Bass Rock after leaving the colony for a stay of a few days to a few weeks, independent of whether they migrated to Africa or other southern areas later. Birds wintering off West Africa migrated to their wintering areas mostly within 3 to 5 wk, usually starting between early and late October. Most of these birds stayed off West Africa for a period of about 3 mo, where they remained in a relatively restricted area. Return migration was initiated between the end of January and mid-February, and took about as long as autumn migration. We conclude that individual gannets display very variable migratory behaviours, with discrete winter home ranges, and we infer that the migration habits of gannets may be changing in response to human impacts on marine ecosystems.

Description: We examined the influence of both season and hydrographic and meteorological factors on seabird abundance in the southern North Sea. Seabirds were counted from ships in a study area of 27.8 x 32.8 km on 407 d from 1990 to 2007. Two hydrographic and 5 meteorological parameters were taken from archived data. The relationships between bird abundance and abiotic parameters were investigated by generalised additive models for 3 distinct seasons. The species in the study area exhibited different seasonal patterns. While some species were present year-round, others occurred only at certain periods. Despite these substantial changes in abundances, the nature of the interactions between bird abundances and abiotic parameters did not vary much between seasons. All 5 meteorological and 2 hydrographic parameters significantly influenced the abundance of seabird species, though to a different degree. The single factors that most often had a significant influence in the single models were wind field, sea surface temperature anomaly, sea surface salinity anomaly and air pressure change. The quantitative composition of the seabird community differed significantly between onshore wind and offshore wind conditions. It is assumed that hydrographic parameters are relevant for the birds by determining their foraging habitats and that atmospheric parameters influence flight conditions during foraging and migration.

Description: Ecological stoichiometry can be a powerful tool to understand food web consequences of altered biogeochemical cycles as well as consequences of biodiversity loss on biogeochemistry and has proved to be a suitable framework to predict effects of consumers on the nutrient content of their prey. However, predictions from ecological stoichiometry have mainly been tested using single consumer species, whereas in most natural ecosystems several consumer species coexist. We conducted 2 outdoor mesocosm experiments with marine rock pool communities to test whether species richness and species combination of benthic invertebrates affected the nutrient content of periphyton. We independently manipulated 12 different consumer combinations ranging from 0 to 6 (2004) or 0 to 4 (2005) grazer species and measured the biomass and nutrient content of the algae. Grazers included 3 gastropods and 3 crustaceans. In 2005, we additionally analyzed animal nutrient content and N excretion rate. Algal biomass and C:N ratios decreased in the presence of grazers in both years, indicating that the remaining algae had higher internal N content. Also, both biomass (2004 and 2005) and C:N ratios (only 2004) decreased even further when grazer richness increased. In 2004, significant net diversity effects of grazer richness on periphyton C:N ratios indicated that periphyton N content under multispecies grazing could not be predicted from the effect of single species. In 2005, significant net diversity effects on C:N ratios were rare, but periphyton C:N ratios consistently decreased with increasing grazer excretion rate, indicating that higher nitrogen regeneration by grazers led to higher N incorporation by algae. The effects of species richness were mainly affected by the presence of one efficient grazer, the gastropod Littorina littorea. Our experiments indicate that non-additive intraguild interactions may qualitatively alter the stoichiometric effects of multispecies consumer assemblages.

Description: It is widely assumed that the production of secondary metabolites against grazing and fouling is costly for seaweeds in terms of metabolic energy and should therefore be reduced under conditions of resource limitation. Here we tested the hypothesis that anti-herbivore defenses and bioactivity against mussels in 4 brown seaweeds from northern-central Chile will be reduced when light is limited. In a 2 wk experiment, seaweeds were kept under different low-light conditions (~76 to 99% reduction of ambient sunlight) and grazing situations. Subsequently, we tested their anti-herbivore defense against a common amphipod grazer in feeding assays with living algal tissue and reconstituted food pellets. A standard test employing the production of byssus threads by mussels was furthermore used as an indicator for deterrents in crude algal extracts. All investigated seaweeds showed decreased growth under the stepwise light reduction. Lessonia nigrescens exhibited reduced defense ability under severe low-light conditions when living tissue was offered to the amphipod, probably caused by changes in the tissue structure or in nutritional traits. In Dictyota kunthii, L. trabeculata and Macrocystis integrifolia this effect was absent. None of the investigated seaweeds showed a clear effect of light reduction on chemically mediated defenses against the mesograzer and there was no effect of light limitation on the bioactivity against mussels. Thus, against general assumptions, chemical defense in the investigated seaweeds does not appear to be reduced under severe resource limitation. Results suggest that seaweeds may use different strategies of energy allocation to cope with low-light conditions.

Description: We describe an integrated database on European macrobenthic fauna, developed within the framework of the European Network of Excellence MarBEF, and the data and data integration exercise that provided its content. A total of 44 datasets including 465354 distribution records from soft-bottom macrobenthic species were uploaded into the relational MacroBen database, corresponding to 22897 sampled stations from all European seas, and 7203 valid taxa. All taxonomic names were linked to the European Register of Marine Species, which was used as the taxonomic reference to standardise spelling and harmonise synonymy. An interface was created, allowing the user to explore, subselect, export and analyse the data by calculating different indices. Although the sampling techniques and intended use of the datasets varied tremendously, the integrated database proved to be robust, and an important tool for studying and understanding large-scale long-term distributions and abundances of marine benthic life. Crucial in the process was the willingness and the positive data-sharing attitude of the different data contributors. Development of a data policy that is highly aware of sensitivities and ownership issues of data providers was essential in the creation of this goodwill.

Description: Deep-sea whale falls create sulfidic habits Supporting chemoautotrophic communities, but microbial processes underlying the formation Of Such habitats remain poorly evaluated. Microbial degradation processes (sulfate reduction, methanogenesis) and biogeochemical gradients were studied in a whale-fall habitat created by a 30 t whale carcass deployed at 1675 m depth for 6 to 7 yr on the California margin. A variety of measurements were conducted including photomosaicking, microsensor measurements, radio-tracer incubations and geochemical analyses. Sediments were Studied at different distances (0 to 9 in) from the whale fall. Highest microbial activities and steepest vertical geochemical gradients were found within 0.5 m of the whale fall, revealing ex situ sulfate reduction and in vitro methanogenesis rates of up to 717 and 99 mmol m(-2) d(-1), respectively. In sediments containing whale biomass, methanogenesis was equivalent to 20 to 30%, of sulfate reduction. During in vitro sediment studies, sulfide and methane were produced within days to weeks after addition of whale biomass, indicating that chemosynthesis is promoted at early stages of the whale fall. Total sulfide production from sediments within 0.5 m of the whale fall was 2.1 +/- 3 and 1.5 +/- 2.1 mol d(-1) in Years 6 and 7, respectively, of which similar to 200 mmol d(-1) were available as free sulfide. Sulfate reduction in bones was much lower, accounting for a total availability of similar to 10 mmol sulfide d(-1). Over periods of at least 7 yr, whale falls can create sulfidic conditions similar to other chemosynthetic habitats Such as cold seeps and hydrothermal vents.

Description: Latitudinal clines in species diversity in limnic and terrestrial habitats have been noted for well over a century and are consistent across many taxonomic groups. However, studies in marine systems over the past 2 to 3 decades have yielded equivocal results. We conducted initial analyses of the MarBEF (EU Network of Excellence for Marine Biodiversity and Ecosystem Function) database to test for trends in local and regional diversity over the latitudinal extent of European continental-shelf waters (36° to 81°N). Soft-sediment benthic macrofauna exhibit little evidence of a latitudinal cline in local (α-) diversity measures. Relationships with water depth were relatively strong and complex. Statistically significant latitudinal trends were small and positive, suggesting a modest increase in diversity with latitude once water-depth covariates were removed. These results are consistent regardless of whether subsets of the database were used, replicates were pooled, or component taxonomical groups were evaluated separately. Local and regional diversity measures were significantly and positively correlated. Scientific cooperation through data-sharing is a powerful tool with which to address fundamental ecological and evolutionary questions relating to large-scale patterns and processes.

Description: This study examines whether or not biogeographical and/or managerial divisions across the European seas can be validated using soft-bottom macrobenthic community data. The faunal groups used were: all macrobenthos groups, polychaetes, molluscs, crustaceans, echinoderms, sipunculans and the last 5 groups combined. In order to test the discriminating power of these groups, 3 criteria were used: (1) proximity, which refers to the expected closer faunal resemblance of adjacent areas relative to more distant ones; (2) randomness, which in the present context is a measure of the degree to which the inventories of the various sectors, provinces or regions may in each case be considered as a random sample of the inventory of the next largest province or region in a hierarchy of geographic scales; and (3) differentiation, which provides a measure of the uniqueness of the pattern. Results show that only polychaetes fulfill all 3 criteria and that the only marine biogeographic system supported by the analyses is the one proposed by Longhurst (1998). Energy fluxes and other interactions between the planktonic and benthic domains, acting over evolutionary time scales, can be associated with the multivariate pattern derived from the macrobenthos datasets. Third-stage multidimensional scaling ordination reveals that polychaetes produce a unique pattern when all systems are under consideration. Average island distance from the nearest coast, number of islands and the island surface area were the geographic variables best correlated with the community patterns produced by polychaetes. Biogeographic patterns suggest a vicariance model dominating over the founder-dispersal model except for the semi-closed regional seas, where a model substantially modified from the second option could be supported.

Description: One of the mysteries regarding Earth’s climate system response to variations in solar output is how the relatively small fluctuations of the 11-year solar cycle can produce the magnitude of the observed climate signals in the tropical Pacific associated with such solar variability. Two mechanisms, the top-down stratospheric response of ozone to fluctuations of shortwave solar forcing and the bottom-up coupled ocean-atmosphere surface response, are included in versions of three global climate models, with either mechanism acting alone or both acting together. We show that the two mechanisms act together to enhance the climatological off-equatorial tropical precipitation maxima in the Pacific, lower the eastern equatorial Pacific sea surface temperatures during peaks in the 11-year solar cycle, and reduce low-latitude clouds to amplify the solar forcing at the surface.

Description: Submarine mud volcanism represents an important. pathway for methane from deeper reservoirs to the surface, where it enters the benthic carbon cycle. To quantify overall methane release from the Captain Arutyunov mud volcano (CAMV) and to assess the contribution of macrobenthic seep organisms to the regulation of the benthic methane flux, we linked water column methane concentrations, seabed methane emission and pore water geochemistry to the spatial distribution of seep biota. Prominent organisms of the CAMV seep biota were 3 different species of frenulate tubeworms. Seabed methane emission ranged from 0.001 to 0.66 mmol m(-2) d(-1). Dense patches of tubeworms were associated with the lowest seabed methane emission. Elevated methane emission was associated with a sporadic distribution of tubeworms and the occurrence of numerous mud clasts. Despite the presence of a large subsurface methane reservoir, the estimated total methane release from CAMV was low (0.006 x 10(6) mol yr(-1)). In addition to direct methane consumption by Siboglinum poseidoni, the tubeworms likely contribute to the retention of methane carbon in the sediment by affecting bacterial communities in the proximity of the tubes. The siboglinids create new meso-scale habitats on the sediment Surface, increasing habitat heterogeneity and introducing niches for bacterial communities.

Description: The oceans are a major sink for atmospheric carbon dioxide (CO2). Historically, observations have been too sparse to allow accurate tracking of changes in rates of CO2 uptake over ocean basins, so little is known about how these vary. Here, we show observations indicating substantial variability in the CO2 uptake by the North Atlantic on time scales of a few years. Further, we use measurements from a coordinated network of instrumented commercial ships to define the annual flux into the North Atlantic, for the year 2005, to a precision of about 10%. This approach offers the prospect of accurately monitoring the changing ocean CO2 sink for those ocean basins that are well covered by shipping routes.

Description: Epibacterial communities on thalli of the algal species Fucus serratus, Fucus vesiculosus, Laminaria saccharina, Ulva compressa, Delesseria sanguinea and Phycodrys rubens were analysed using 16S ribosomal RNA gene-based DGGE. Individuals of all species were collected in the Kiel Fjord (Baltic Sea) and in the rocky intertidal of Helgoland (North Sea). DGGE gels as well as cluster and multidimensional scaling analysis based on the DGGE band patterns of the epibacterial community showed significant differences between the epibacterial communities on the investigated algal species both in the Baltic and North Seas. Epibacterial communities differed less between regions than between host species, and were more similar on closely related host species. Results give the first evidence for lineage-specific bacterial associations to algal thalli. Furthermore, the results suggest that these algal species may control their epibiotic bacterial communities.

Description: Picoeukaryotes are a taxonomically diverse group of organism less than 2 micrometers in diameter. Photosynthetic marine picoeukaryotes in the genus Micromonas thrive in ecosystems ranging from tropical to polar and could serve as sentinel organisms for biogeochemical fluxes of modern oceans during climate change. These broadly distributed primary producers belong to an anciently diverged sister clade to land plants. Although Micromonas isolates have high 18S ribosomal RNA gene identity, we found that genomes from two isolates shared only 90 of their predicted genes. Their independent evolutionary paths were emphasized by distinct riboswitch arrangements as well as the discovery of intronic repeat elements in one isolate, and in metagenomic data, but not in other genomes. Divergence appears to have been facilitated by selection and acquisition processes that actively shape the repertoire of genes that are mutually exclusive between the two isolates differently than the core genes. Analyses of the Micromonas genomes offer valuable insights into ecological differentiation and the dynamic nature of early plant evolution.

Description: The cirrate octopod Stauroteuthis syrtensis is a mesopelagic species commonly collected in the North Atlantic. Individuals were observed at depths 〉600 m and typically within 100 m of the bottom in three ~900 m deep canyons indenting the southern edge of Georges Bank. When first sighted, most octopods were floating passively with their webbed arms gathered into a small ball. When disturbed, they expanded their webs to form a ‘balloon’ shape, swam slowly by sculling their fins, pulsed their webs like medusae and, in some cases, streamlined their arms and webs and moved away smoothly by rapidly sculling their fins. The bodies of 9 octopods comprised 92 to 95% water, with tissue containing 9 to 22% carbon (C) and 2 to 4% nitrogen (N). These values were similar to those reported for medusae and ctenophores. Oxygen (O2) consumption rates of 4.6 to 25.8 µmol O2 g–1 C h–1 were within ranges reported for medusae, ctenophores, and deep-water cephalopods. The stomachs of S. syrtensis, dissected immediately after capture, contained only the calanoid copepod Calanus finmarchicus. Calculations indicated that S. syrtensis need 1.3 to 30.1 ind. d–1 of C. finmarchicus to meet their measured metabolic demand. Excretion rates (0.3 to 12.4 µg NH4+ g–1 C h–1 and 0.06 to 4.83 µg PO43– g–1 C h–1) were at least an order of magnitude lower than rates reported for other octopods or gelatinous zooplankters. O:N ratios (11 to 366) suggested that S. syrtensis catabolized lipids, which may be supplied by C. finmarchicus. Vertical distribution, relatively torpid behavior and low metabolic rates characterized S. syrtensis as a benthopelagic and relatively passive predator on copepods.

Description: The North Pacific Ocean population of the neon flying squid Ommastrephes bartramii, which undertakes seasonal north–south migrations, consists of autumn and winter–spring spawning cohorts. We examined life history differences between the 2 cohorts in relation to the oceanographic environment. The differences could be explained by seasonal north–south movements of the following 2 oceanographic zones: (1) the optimum spawning zone defined by sea surface temperatures; and (2) the food-rich zone defined by the position of the transition zone chlorophyll front (TZCF). The 2 cohorts use the food-rich zone in different phases of their life cycles. The spawning grounds for the autumn cohort occur within the subtropical frontal zone (STFZ), characterized by enhanced productivity in winter due to its proximity to the TZCF, whereas the spawning grounds for the winter–spring cohort occur within the subtropical domain, which is less productive. As the TZCF shifts northward in spring, the autumn cohort continues to occur in the productive area north of the TZCF, whereas the winter–spring cohort remains in the less productive area to the south until it migrates into productive waters north of the TZCF in the summer or autumn. Consequently, the autumn cohort grows faster than the winter–spring cohort during the first half of its life cycle, whereas the winter–spring cohort grows faster during the second half. This growth pattern may be responsible for differing migration patterns; males of the autumn cohort do not have to migrate given their early fast growth in the STFZ, whereas those of the winter–spring cohort must migrate to the food-rich subarctic frontal zone to compensate for their slow growth. These biological and ecological differences between the 2 cohorts suggest flexibility of their life history response to oceanographic environments.

Description: Highly stratified marine ecosystems with dynamic features such as fronts or clines in salinity, temperature, or oxygen concentration challenge an individual’s ability to select suitable living conditions. Ultimately, environmental heterogeneity organizes the spatial distributions of populations and hence the spatial structure of the ecosystem. Our aim here is to present a method to resolve small-scale distribution on an individual level, as needed for the behaviorally-based prediction of habitat choice and limits. We focused on the small-scale vertical distribution of cod Gadus morhua L. in the Bornholm Basin, central Baltic Sea, during spawning time in 2 years with different vertical thermohaline and oxygen stratifications. Individual cod were identified by echotracking of real-time in situ hydroacoustic distribution data. In order to resolve and identify hydrographic preferences and limits, ambient parameters including temperature, salinity, and oxygen concentration as well as expected egg-survival probability were individually allocated to each fish. The vertical distribution of hydroacoustically identified fish was compared to data simultaneously recorded by data storage tags attached to cod. The results showed a clear influence of ambient salinity and oxygen concentration on the distribution pattern and distributional limitation of cod during spawning time, and also consistency of data storage tag-derived distribution patterns with those based on individual echotracking. We therefore consider this method to be a useful tool to analyze individual behavior and its implications for the population’s spatial distribution in stratified environments.

Description: Phytoplankton supply the base of the marine food web and drive the biogeochemical cycles of carbon and nutrients. Over much of the ocean, their growth is limited by their uptake of nitrogen (as nitrate), which has most commonly been described by the hyperbolic Michaelis-Menten (MM) equation. However, the lack of a theory to explain variations in MM constants has hindered our ability to predict the response of marine ecosystems to changes in environmental conditions. The MM equation fits data from short-term experiments well, but does not agree with steady-state experiments over wide ranges of nutrient concentrations. In contrast, the recently developed optimal uptake kinetics (OU) does agree with the latter and can also describe the observed pattern of MM half-saturation constants from field. experiments. OU kinetics explains the observed pattern of N uptake as the result of a general physiological trade-off between nutrient uptake capacity and affinity. The existence of a general trade-off would imply a relatively high degree of predictability in the response of nutrient uptake to changing nutrient concentrations and thus provide a basis for predicting effects of climate change on marine ecosystems and biogeochemical cycles.

Description: Particulate (POM) and dissolved organic matter (DOM) released by the cold water corals Lophelia pertusa (L.) and Madrepora oculata (L.) was collected, analysed and quantitatively compared to that released by warm water reef-building corals. Particulate nitrogen (PN) and particulate organic carbon (POC) release rates of L. pertusa were 0.14 ± 0.07 mg N m–2 h–1 and 1.43 ± 1.22 mg C m–2 h–1, respectively, which is in the lower range of POM release rates measured for warm water corals, while dissolved organic carbon (DOC) release was 47 ± 19 mg C m–2 h–1. The resulting high DOC:POC ratio indicates that most cold water coral-derived organic matter immediately dissolved in the water column. Cold water corals, similar to their warm water counterparts, produced large amounts of nitrogen-rich coral mucus with C:N ratios of 5 to 7 for Lophelia- and 7 to 9 for Madrepora-derived mucus. A 7-fold increase in the oxygen consumption rates in cold water coral mucus-amended seawater containing the natural microbial assemblage indicates that this organic matter provided an attractive food source for pelagic microbes. In situ investigations at Røst Reef, Norway, showed that microbial activity in the seawater closest to the reef was 10 times higher than in the overlying water column. This suggests that cold water corals can stimulate microbial activity in the direct reef vicinity by the release of easily degradable and nutrient-rich organic matter, which may thereby function as a vector for carbon and nutrient cycling via the microbial loop in cold water coral reef systems.

Description: The recent introduction of Gracilaria vermiculophylla (Rhodophyta) to the Kiel Fjord area was a reason for concern, since this red macroalga performs best under mesohaline conditions and thus appears well adapted to thrive and spread in the Baltic Sea environment, A systematic survey on a coastal range of 500 km in 2006 and 2007 indicated considerable Multiplication and spreading of G. vermiculophylla within Kiel Fjord, but provided little evidence of long-distance transport. Nonetheless, flow-through growth experiments conducted at a range of salinities under ambient light showed that G. vermiculophylla should be able to grow in most of the Baltic Sea. Growth declined only below a salinity of 5.5. High water temperatures in summer seem to reduce resistance against low salinity. Growth of G, vermiculophylla in the SW Baltic is limited by light and is only possible during summer and above a depth of 3 m. Drifting fragments are dispersed by currents. Either they sink to deeper waters, where they degrade, or they accumulate in shallow and sheltered waters, where they form perennial mats. These overgrow not only soft bottom sediments, but also stones, which are an important habitat to Fucus vesiculosus, the main native perennial alga in the Baltic Sea. As compared to F. vesiculosus, G. vermiculophylla seems to represent a preferred refuge for mesograzers and other invertebrates, particularly in winter. Nonetheless, feeding trials showed that potential grazers avoided G. vermiculophylla relative to F vesiculosus. Daily biomass uptake by grazers associated with G. vermiculophylla in nature did not exceed 2 g kg(-1) and is 〈11% of average daily net growth (18.5 g kg(-1)) in the first 2 m below sea level. Consequently, feeding may not be sufficient to control the spread of G. vermiculophylla in the SW Baltic. Our study suggests that absence of feeding enemies and adaptation to brackish water may allow G. vermiculophylla to invade most shallow coastal waters of the inner Baltic Sea despite light limitation.

Description: Ocean acidification and associated changes in seawater carbonate chemistry negatively influence calcification processes and depress metabolism in many calcifying marine invertebrates. We present data on the cephalopod mollusc Sepia officinalis, an invertebrate that is capable of not only maintaining calcification, but also growth rates and metabolism when exposed to elevated partial pressures of carbon dioxide (pCO(2)). During a 6 wk period, juvenile S. officinalis maintained calcification under similar to 4000 and similar to 6000 ppm CO2, and grew at the same rate with the same gross growth efficiency as did control animals. They gained approximately 4%, body mass daily and increased the mass of their calcified cuttlebone by over 500 %. We conclude that active cephalopods possess a certain level of pre-adaptation to long-term increments in carbon dioxide levels. Our general understanding of the mechanistic processes that limit calcification must improve before we can begin to predict what effects future ocean acidification will have on calcifying marine invertebrates.

Description: Effects of global warming on marine ecosystems are far less understood than they are in terrestrial environments. Macrophyte-based coastal ecosystems are particularly vulnerable to global warming, because they often lack species redundancy. We tested whether summer heat waves have negative effects on an ecologically important ecosystem engineer, the eelgrass Zostera marina L., and whether high genotypic diversity may provide resilience in the face of climatic extremes. In a mesocosm experiment, we manipulated genotypic diversity of eelgrass patches fully crossed with water temperature (control vs. temperature stress) over 5 mo. We found a strong negative effect of warming and a positive effect of genotypic diversity on shoot densities of eelgrass. These results suggest that eelgrass meadows and associated ecosystem services will be negatively affected by predicted increases in summer temperature extremes. Genotypic diversity may provide critical response diversity for maintaining seagrass ecosystem functioning, and for adaptation to environmental change.

Description: The diazotrophic cyanobacterium Trichodesmium is a significant contributor to marine nitrogen and carbon cycles and has been incorporated in biogeochemical ocean circulation models. To date, parameterization of light as a controlling factor for nitrogen fixation has been based on field observations, where factors other than light also affect Trichodesmium physiology. Here we present data on light-dependent (15 to 1100 µmol quanta m–2 s–1) diazotrophic growth from controlled laboratory experiments and their implications for modeling approaches. We supply a simple empirical model to describe nitrogen fixation by Trichodesmium in batch cultures. Diazotrophic growth of axenic Trichodesmium IMS-101 was light saturated at 180 µmol quanta m–2 s–1 and did not vary significantly at higher photon irradiances up to 1100 µmol quanta m–2 s–1 (μcarbon based ≈ 0.26 d–1). Chlorophyll a (chl a) normalized N2 fixation rates were significantly affected by light intensity during mid-exponential growth (0.74 to 4.45 mol N fixed mol chl a–1 h–1) over the range of photon irradiances tested. In contrast, nitrogen fixation rates normalized to the cellular carbon content were relatively unaffected by light intensity (0.42 to 0.59, averaging 0.5 mmol N mol particulate organic carbon [POC]–1 h–1). Trichodesmium carbon biomass can be used to estimate the nitrogen input by this diazotroph into the ocean; the maximum input rate is 350 nmol N fixed l–1 h–1.

Description: Multiple stable isotope and fatty acid analyses were applied to examine food web dynamics in an eelgrass Zostera marina L. system in the western Baltic Sea. Samples of eelgrass, epiphytic algae, sand microflora, red algae, phytoplankton and main consumer species were collected in June 2002. delta C-13 values of primary producers ranged from -9.6%. for eelgrass to the most depleted value of -34.9%. for the most abundant red alga, Delesseria sanguinea, Epiphyte delta C-13 (-11.3 parts per thousand.) was close to the value for eelgrass, whereas sand microflora and phytoplankton showed intermediate values (-20.0 and -22.6 parts per thousand, respectively). delta C-13 values of consumer species varied from - 12.2 parts per thousand in the gastropod Lacuna vincta to -23.9 parts per thousand in the amphipod Amphitoe rubricata. Epiphytes, sand microflora and phytoplankton had relatively similar fatty acid signatures, indicating a dominance of diatoms. Fatty acid composition of the main consumers included the biomarker fatty acids for diatoms and red algae, whereas those for eelgrass were negligible. The stable isotope data in combination with the results of the fatty acid analysis strongly indicated that the food web in this eelgrass community was based on epiphytes, sand microflora and red algae. Additionally, the continuous distribution of delta N-15 values implied a food web that was characterized by a large proportion of generalist feeders in every group of consumers and by a high degree of omnivory.

Description: Weight-specific growth rate (G) and growth performance (the fraction of maximum growth realized, G pf) are key demographic characteristics. The ratio of RNA/DNA (RD) can provide information on both G and G pf. Estimating G from RD in larval fish requires an adjustment for the activity of RNA at different temperatures. Based on a meta-analysis of published data, we present a general model for the relationship between G in marine fish larvae and fluorometrically derived RD and temperature (T), and suggest that this model can be used to estimate G in marine fish larvae. Several options for estimating G pf are also considered, including the use of a reference growth rate (Gref). RDs of well-fed larvae appeared to be independent of water temperatures between 4 and 28°C, suggesting that any increase in growth rate with temperature was accomplished by increased activity rather than increased concentrations of RNA. However, for the best-fit meta-analysis RD–T–G model, the relationship between RD and G pf was temperature dependent for fish less than fully fed.

Description: The response of the phytoplankton and bacterial spring succession to the predicted warming of sea surface temperature in temperate climate zones during winter was studied using an indoor-mesocosm approach. The mesocosms were filled with winter water from the Kiel Fjord, Baltic Sea. Two of them were started at ~2°C and the temperature was subsequently increased according to the decadal temperature profile of the fjord (ΔT 0°C, baseline treatment). The other mesocosms were run at 3 elevated temperatures with differences of ΔT +2, +4 and +6°C. All mesocosms were exposed to the same light conditions. Timing of peak phytoplankton primary production (PP) during the experimental spring bloom was not significantly influenced by increasing temperatures, whereas the peak of bacterial secondary production (BSP) was accelerated by about 2 d per °C. This suggests that, in case of warming, the spring peak of bacterial degradation of organic matter (in terms of BSP) would occur earlier in the year. Furthermore, the lag time between the peaks of PP and BSP (about 16 d for ΔT 0°C) would diminish progressively at elevated temperatures. The average ratio between BSP and PP increased significantly from 0.37 in the coldest mesocosms to 0.63 in the warmest ones. Community respiration and the contribution of picoplankton (〈3 µm fraction) to this also increased at elevated temperatures. Our results lead to the prediction that climate warming during the winter/ early spring in temperate climate zones will favor bacterial degradation of organic matter by tightening the coupling between phytoplankton and bacteria. However, if PP is reduced by warming, as in our experiments, this will not necessarily lead to increased recycling of organic matter (and CO2).

Description: Ocean acidification and associated changes in seawater carbonate chemistry negatively influence calcification processes and depress metabolism in many calcifying marine invertebrates. We present data on the cephalopod mollusc Sepia officinalis, an invertebrate that is capable of not only maintaining calcification, but also growth rates and metabolism when exposed to elevated partial pressures of carbon dioxide (pCO2). During a 6 wk period, juvenile S. officinalis maintained calcification under ~4000 and ~6000 ppm CO2, and grew at the same rate with the same gross growth efficiency as did control animals. They gained approximately 4% body mass daily and increased the mass of their calcified cuttlebone by over 500%. We conclude that active cephalopods possess a certain level of pre-adaptation to long-term increments in carbon dioxide levels. Our general understanding of the mechanistic processes that limit calcification must improve before we can begin to predict what effects future ocean acidification will have on calcifying marine invertebrates.

Description: The community composition of denitrifying bacteria was studied in the stratified water column of Lake Kinneret. The nitrite reductase genes nirS and nirK were amplified by PCR from water samples taken at 1, 14, 19 and 22 m depth, which represent the epi-, meta- and hypolimnion of the lake. The PCR products were analyzed with terminal restriction fragment length polymorphism (T-RFLP) and clone libraries. The highest diversity of nirS denitrifying communities was observed at 1 m depth. According to the T-RFLP profiles and clone libraries of nirS products, 2 groups of denitrifiers were common to and dominant in all depths. Deduced protein sequences from one of these groups displayed low identity (77%) with other nirS sequences reported in GenBank. Denitrifying bacterial communities with nirK were most diverse at 22 m and showed highest similarity to those at 19 m depth. Sequences unrelated to nirK dominated the clone libraries from 1 m depth, suggesting that denitrifying bacteria with copper-containing nitrite reductase were less frequent at this depth. The results suggest that microorganisms with nirK and those with nirS respond differently to the environmental conditions in the stratified water column of Lake Kinneret.

Description: The effects of towed fishing gear on benthic fauna are under intense scrutiny and evidence is growing that trawling may significantly affect benthic communities in the North Sea. Most studies explore the current fauna or compare today’s situation with that of 2 or 3 decades ago, when North Sea-wide information on benthos and fishing became available. However, in the North Sea, extensive mechanised trawling began more than a century ago. This study compared historical and recent records in order to explore potential long-term links between changes in the epibenthos and fishing. Based on reconstructed species lists from museum specimens, we compared epibenthos data from 1902 to 1912 with those from 1982 to 1985 and 2000. We analysed changes in average taxonomic distinctness (AvTD), a biodiversity indicator, and changes in biogeographical species distributions. Landings data were collated for round- and flatfish caught in the northern, central and southern North Sea from 1906 to 2000 as proxies for total otter and beam trawl effort, respectively. These indicate that the southern and much of the central North Sea were fished intensively throughout the 20th century, whilst the northern North Sea was less exploited, especially in earlier decades; exploitation intensified markedly from the 1960s onwards. For epibenthos, the mean AvTD decreased significantly from the 1980s to 2000, when it was below expected values in 4 ICES rectangles, 3 of these located in heavily trawled areas. Biogeographical changes from the beginning to the end of the century occurred in 27 of 48 taxa. In 14 taxa, spatial presence was reduced by 50% or more, most notably in the southern and central North Sea; often these were long-lived, slow-growing species with vulnerable shells or tests. By contrast, 12 taxa doubled their spatial presence throughout the North Sea. Most biogeographical changes had happened by the 1980s. Given that other important environmental changes, including eutrophication and climate change, have gained importance mainly from the 1980s onwards, we have concluded that the changes in epibenthos observed since the beginning of the 20th century have resulted primarily from intensified fisheries.

Description: Physical and chemical properties of the water column, along with meteorological conditions were examined for their relationship with phytoplankton biomass in the Irminger Sea during late autumn and early winter. Data were collected during 2 cruises to the region in November and December 2001 and November 2002. Phytoplankton biomass was approximated by (chl a) concentrations within the water column. When examined during autumn and winter alone, the Irminger Sea was suitably described as one biogeochemical region responding to varying meteorological forcing. Hydrographic differences within the region were not observed to have a significant effect on phytoplankton growth during this period. Strong correlations with latitude were seen in chl a concentrations, physical conditions (including mixed layer depth) and meteorological forcing (including net heat flux). Variability in autumn/winter phytoplankton growth conditions appears to be driven by light limitation modulated by meteorological forcing. The temporal and spatial scales of locations sampled in 2001 represent a progression in the physical and biological conditions from late autumn to early winter. Along this ‘virtual transect’, a baseline value of approximately 0.1 mg m–3 is seen in the mean chl a concentrations within the mixed layer. We postulate that convection provides a mechanism for reduction of net losses of phytoplankton, by helping to keep phytoplankton within the mixed layer. Under such conditions, a deeper and therefore more accurate estimation of the critical depth would be valid. Evidence of the extended maintenance of phytoplankton within the mixed layer is presented in the form of the relative dominances of different phytoplankton groups.

Description: Sponges (phylum Porifera) are among the most ancient of the multicellular animals, or Metazoa, with a fossil record dating back at least 580 million years (1). Found both in marine and freshwater environments, they filter-feed by pumping water through their bodies, which can contain a remarkable number of microbial symbionts. Sponges lack many of the characteristics typical of animals, but recent genomic studies—including the report by Jackson et al. on page 1893 of this issue (2)—have shown that they possess many major metazoan gene families. Sponges are thus invaluable systems for studying the evolution of metazoans and their interactions with microorganisms. Furthermore, their highly stable skeletons are of interest to materials scientists. Biomineralization is an important feature of metazoan life. Animals including vertebrates, insects, mollusks, and sponges use minerals [such as calcium carbonate, iron, and silica] to form skeletal structures such as bones, seashells, and coral reefs (3). Biocalcification arose among many metazoan lineages during the “Cambrian explosion,” between 530 and 520 million years ago, when the ancestors of today's animals first appeared in the fossil record. Did these lineages share the same gene(s) for biocalcification, or did multiple independent evolutionary events give rise to the ability to biocalcify? Recent studies, including that by Jackson et al., are beginning to provide an answer to this question. Jackson et al. use the Indo- Pacific sponge Astrosclera willeyana to show that the last common ancestor of the metazoans possessed a precursor to the α-carbonic anhydrases. This gene family is used by animals today in a range of processes including ion transport, pH regulation, and biomineralization (4). By integrating molecular techniques ranging from protein sequencing to gene expression, the authors identified a group of closely related α-carbonic anhydrase sequences in A. willeyana. These sequences are similar to those recovered from a whole-genome project on another sponge, Amphimedon queenslandica (5). Together, the sponge α-carbonic anhydrases form a sister group to those of all other metazoans.

Description: Bacteria were isolated seasonally from the Mediterranean sponges Chondrilla nucula and Petrosia ficiformis and screened for antibacterial activities. Selected isolates were taxonomically identified by 16S rRNA gene sequencing. A total of 416 different bacterial strains were isolated, 60 (14.4%) of which displayed variable degrees of antimicrobial activity. Of the bioactive strains, 58.3% were able to inhibit Staphylococcus aureus, 6.7% were active against Bacillus subtilis, 11.7% against both Enterococcus faecalis and Escherichia coli, 38.3% against Pseudoalteromonas atlantica and 33.3% against Pseudomonas elongata. 16S rRNA gene sequence analysis showed that 2 isolates, 1 from seawater samples and 1 from P. ficiformis, were most closely related to Bacillus subtilis (99% similarity) and that another isolate from P. ficiformis was most closely related to a previously described sponge-associated Alphaproteobacterium NW001 (98% similarity). Two isolates from C. nucula were most closely related to Brachybacterium paraconglomeratum (99% similarity) and Shewanella algae (89% similarity). The high percentage of bioactive isolates derived from the 2 sponges suggests that marine microorganisms, whether animal-associated or planktonic, are promising sources for drug discovery.

Description: The Atlantic meridional overturning circulation (MOC), which provides one-quarter of the global meridional heat transport, is composed of a number of separate flow components. How changes in the strength of each of those components may affect that of the others has been unclear because of a lack of adequate data. We continuously observed the MOC at 26.5°N for 1 year using end-point measurements of density, bottom pressure, and ocean currents; cable measurements across the Straits of Florida; and wind stress. The different transport components largely compensate for each other, thus confirming the validity of our monitoring approach. The MOC varied over the period of observation by ±5.7 × 106 cubic meters per second, with density-inferred and wind-driven transports contributing equally to it. We find evidence for depth-independent compensation for the wind-driven surface flow.

Description: We investigated connections between subtropical Atlantic climate variability, atmospheric conditions in the European Alpine region (45 to 47° N and 5 to 8° E) and the interannual variability of the thermal conditions in the largest body of freshwater in Western Europe (Lake Geneva). The long-term water temperature was related to climate variability by means of a multivariate regression model. Results revealed atmospheric connections that have been elusive so far, and showed that over the period from 1959 to 2000, summer thermal conditions in Lake Geneva appear tightly linked to the long-term variability of the subtropical Atlantic climate. The multivariate model revealed high skills and tight correlations, which suggest the possibility of assessing future thermal changes in Lake Geneva from the Atlantic climate variability. The implications of such climatic forcing on the functioning of the pelagic ecosystem in Lake Geneva were illustrated by analysing the long-term changes in abundance of the summer-dominant carnivorous cladocerans Bythotrephes longimanus and Leptodora kindtii during the period 1974 to 2000. Again, the multivariate model revealed high skills and excellent correlations between the interannual changes in abundance of these species and the variability of summer climate. Our approach provides a general understanding of the interrelations between large- and regional-scale climates, local environmental conditions and the ecological responses in Lake Geneva during summer, and is therefore applicable to other retrospective studies.

Description: Bimodal depth distribution patterns observed for sprat Sprattus sprattus larvae in previous field studies conducted in the deep basins of the Baltic Sea have led researchers to hypothesise that larval sprat condition was depth-dependent. We examined this hypothesis by measuring morphological, biochemical and otolith-based proxies for nutritional condition in sprat larvae collected in discrete 5 m depth intervals from the surface to the bottom in the central Bornholm Basin. Similar to earlier studies, larval sprat were most abundant in 2 depth strata (0 to 10 and 65 to 75 m). Their nutritional condition in surface and deep waters was not uniformly expressed by the different indices. For example, sprat larvae from 0 to 10 m could not be distinguished from conspecifics caught at 65 to 75 m by a long-latency condition proxy (otolith-based growth rates). Similarly, a medium-latency proxy (RNA:DNA) did not suggest differences in condition between the depths. However, short-latency proxies (protein:standard length and DNA:dry weight) supported the depth-dependent condition hypothesis. The lack of correspondence and pitfalls associated with the use and interpretation of multiple condition indices (e.g. the influences of temperature and body size) are discussed and recommendations to strengthen these various metrics are provided.

Description: The occurrence of the ctenophore Mnemiopsis leidyi as a new invasive species in the Baltic Sea and the potential consequences for fish stock recruitment was investigated in spring 2007. The study focused on the Bornholm Basin, which serves as the major spawning ground for cod and sprat, the commercially most important fish stocks in the Baltic. The distribution pattern of M. leidyi revealed a substantial overlap with cod eggs. The observed predation of M. leidyi on eggs has the potential to alter the recruitment success of cod, which is the top predator in the system and, thus, to change the Baltic food-web structure.

Description: We investigated the nutritional condition of larval fishes caught in daily ichthyoplankton hauls in the ‘Helgoland Roads’ (54°11.18’N and 07°54.00’E) from February to June 2004. We concentrated on larvae of dab Limanda limanda and lesser sandeel Ammodytes marinus in order to compare early life stages of iteroparous and nearly semelparous fish. We analysed length, weight and RNA:DNA ratios as a proxy for condition of the larvae. The relationship between larval nutritional condition and larval size provided an indication of condition-selective mortality due to a loss of larvae in poor condition from the larger size-classes. For the sandeel, larvae in good condition were present in all size-classes, whereas for the dab maximum larval condition increased with increasing size. Variability in both standard length and condition was high in the 2 species during their planktonic stage. Both species showed good nutritional condition in the early to mid portion of the recruitment period and declines in condition in late April. This was more pronounced in larval dab, which showed a higher dependency on feeding conditions than larval sandeel. Together, these findings indicate a more conservative strategy of early life stages of the nearly semelparous sandeel compared with the iteroparous dab.

Description: The vigor of Atlantic meridional overturning circulation (MOC) is thought to be vulnerable to global warming, but its short-term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain. We combine continuous measurements of the MOC (beginning in 2004) using the purposefully designed transatlantic Rapid Climate Change array of moored instruments deployed along 26.5°N, with time series of Gulf Stream transport and surface-layer Ekman transport to quantify its intra-annual variability. The year-long average overturning is 18.7 ± 5.6 sverdrups (Sv) (range: 4.0 to 34.9 Sv, where 1 Sv = a flow of ocean water of 106 cubic meters per second).

Description: The present study quantifies the spatial heterogeneity of the environmental conditions associated with successful spawning by cod Gadus morhua in the Bornholm Basin. Quarterly means from 1989 to 2003 of the thickness of reproductive volume that enabled egg survival indicate that most favourable spawning conditions were located in the central area, inside the 80 m isobath. On average, spatial patterns were similar in the second and third quarters, but with overall lower thicknesses of reproductive volume and less horizontal extension of conditions suitable for egg survival in the third quarter. The observed basin-wide variation in thickness of reproductive volume and oxygen content inside this volume can result in marked horizontal differences in oxygen-related egg mortality, especially during stagnation years. The spawning habitat selected by adult Baltic cod in the Bornholm Basin was characterised by comparing data on egg abundance with environmental variables measured concurrently with egg collection. A clear preference for spawning at locations in the deep basin is evident after both inflow events, as well as for stagnation periods. In consequence, the closed area for fishing implemented in the Bornholm Basin during the main spawning periods from 1995 to 2003, although located in the northern centre of the basin, did not necessarily ensure undisturbed spawning in stagnation years.

Description: We monitored the dynamics of extracellular organic matter in 3 mesocosms: one dominated by a heterotrophic (microbial) community with negligible autotrophic activity (net heterotrophic system), a second where a small Phaeocystis bloom developed (production and loss almost balanced), and a third harboring a large diatom bloom (net autotrophic system). In all mesocosms, meso- and macroscopic heterotrophic organisms were excluded to primarily study extracellular organic matter production and turnover by specific algae and microbial loop organisms, respectively. Concentration and composition of dissolved organic matter (DOM), i.e. dissolved organic carbon (DOC), monosaccharides and total carbohydrates (MCHO and TCHO), free and combined neutral carbohydrates (DFCHO and DCCHO), as well as free and combined amino acids (DFAA and DCAA) were measured. In addition, net and gross community production rates were determined to calculate C-budgets. Whereas concentrations and composition of MCHO differed very little among the 3 mesocosms, dynamics of TCHO, DFCHO, and DCCHO differed significantly. Concentrations of DFAA were higher in both algal mesocosms compared to the heterotrophic system, and composition of DFAA was significantly different in the Phaeocystis and Diatom tanks. The composition and concentration of DCAA, however, were similar in all 3 mesocosms. Total dissolved carbohydrates and amino acids comprised a substantial fraction of the DOC pool. Dynamics of these DOC fractions, however, could only partly explain those of DOC, implying either that other dissolved compounds were important for overall C-cycling, or that microbial degradation of DOM affects the detection of carbohydrates and protein components.

Description: The effect of phytoplankton on the other compartments of a simple microbial loop consisting of dissolved matter, bacteria and nanoflagellates was investigated in three 1000 l mesocosms. These mesocosms were inoculated with a natural bacterial community and (1) no other additions (No Addition tank), (2) Phaeocystis globosa (Phaeocystis tank), or (3) 2 diatom species (Diatom tank). During the 20 d experiment, autotrophic activity was negligible in the No Addition tank. In contrast a small P. globosa bloom developed in the Phaeocystis tank and a large diatom bloom dominated the Diatom tank. In this paper we describe the experiment, the changes in chlorophyll a and heterotrophic nanoflagellate concentrations, as well as the cycling of nitrogen, phosphorus, and silica. Then we provide a synthesis of the structure and functioning of the microbial loops in these 3 systems using cluster analysis, a statistical pattern recognition tool. The goal was to test the hypothesis that differences in the resident phytoplankton populations would be reflected in (1) the composition and concentration of dissolved organic matter, (2) the composition of the bacterial community, (3) the food web, and (4) the cycling of elements and organic matter. In all 3 mesocosms, nitrate and silicic acid remained abundant. Orthophosphate was preferred by diatoms, whereas Phaeocystis appeared to prefer dissolved organic phosphorus. The hypothesis that phytoplankton composition shapes the structure and functioning of the microbial loop was partially supported: 6 d after inoculation each mesocosm exhibited a distinct organic matter signature. After 10 to 12 d, concentrations of heterotrophic nanoflagellates were high enough to exert significant grazing pressure in all 3 mesocosms. A parallel shift in bacterial community composition was visible in all mesocosms at this time, possibly reflecting grazing pressure. The food-web structure developed divergently in the 3 mesocosms during the second half of the experiment. Differences in biochemical cycling between mesocosms were predominantly driven by the large quantitative differences in autotrophs.

Description: We used data collected at 〉 60 stations over a 10 yr period to build the carbon budget of the plankton community in the euphotic layer of the Eastern North Atlantic Subtropical Gyre (NASE). Autotrophic biomass exceeded microbial heterotrophic biomass by a factor of 1.7. Mean ( SE), integrated chlorophyll a concentration and net particulate primary production (PP) were 17 +/- 1 Mg m(2) and 271 +/- 29 mg C m(-2) d(-1), respectively. Protist grazing on phytoplankton represented 〉 90% of PP. Bacterial production (BP) was 17 +/- 3 mg C m(-2) d(-1). In vitro O-2-evolution experiments indicated that net community production was -65 +/- 16 mmolO(2) m(-2) d(-1), while community respiration (CR) averaged 124 +/- 13 mmolO(2) m(-2) d-1, equivalent to 1324 +/- 142 mg C m(-2) d(-1). However, the sum of the respiration rates by each microbial group, estimated from their biomass and metabolic rates, ranged from 402 to 848 Mg C m(-2) d-1. Therefore, CR could not be reconciled with the respiratory fluxes sustained by each microbial group. Comparison between estimated gross photosynthesis by phytoplankton (481 to 616 mg C m(-2) d-1) and the sum of respiration by each group suggests that the microbial community in the NASE province is close to metabolic balance, which would agree with the observed O-2 supersaturation in the euphotic layer. Taking into account the mean open-ocean values for PP, BP, CR and bacterial growth efficiency, we show that bacteria account for approximately 20% of CR. Our results suggest that the view that bacteria dominate carbon cycling in the unproductive ocean must be reconsidered, or else that in vitro incubations misrepresent the real metabolic rates of one or several microbial groups.

Description: This study explores the date of first otolith increment formation in Baltic sprat Sprattus sprattus and relates the onset of maturity at Age 1 to the larval traits that are tied to the formation of the first increment. From the otolith microstructure analyses in larvae we found that regular deposition of increments is closely related to larval length, the first clear increment being identified at 16 mm length. Otolith distance from the centre to the first clear increment was independent of temperature, whereas the width of subsequent regular increments increased with increasing temperatures. These results are interpreted in the context of the interaction of larval length, somatic growth and environmental temperature. The date of first increment formation was further estimated in mature and immature Age 1 sprat caught from 1998 to 2000 using a technique that we developed, based on the effect of temperature on larval-stage otolith microstructure after first increment formation. The overall result was that larvae that reach the length of 16 mm early (late) in the season in warm years are more (less) likely to mature the following year. In cold years, like 1998, the probability of maturating at Age 1 was independent of the date at which larvae became 16 mm long, and other processes such as juvenile growth rates, feeding conditions and year-class abundance are suggested as factors that may influence the onset of maturity.

Description: Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided.