ALBERT

Description: Estuaries are among the most valuable aquatic systems in terms of their services to human welfare. They offer an ideal framework to assess multiscale processes linking climate and food web dynamics through the hydrological cycle. Resolving food web responses to climate change is fundamental to resilience management of these threatened ecosystems under global change scenarios. Here, we examined the temporal variability of the plankton food web in the Mondego Estuary, central Iberian Peninsula, over the period 2003 to 2012. The results pointed out a cascading effect from climate to plankton communities that follow a non-stationary behavior shaped by the climate variance envelope. Concurrent changes in hydrographic processes at the regional, that is, upwelling intensity, and local, that is, estuarine hydrology, scales were driven by climatic forcing promoted by the North Atlantic Oscillation; the influence of which permeated the physical environment in the estuary affecting both autotrophic and heterotrophic communities. The most conspicuous change arose around 2008 and consisted of an obvious decrease in freshwater taxa along with a noticeable increase in marine organisms, mainly driven by gelatinous zooplankton. The observed increase in small-sized cosmopolitan copepods, that is, Clausocalanus arcuicornis, Oithona plumifera, thermophilic species, that is, Penilia avirostris, and gelatinous zooplankton suggests a structural change in the Mondego plankton community. These results provide empirical support to the expectation that expanding climate variance changes plankton structure and functioning, likely fostering trophic interactions in pelagic food webs.

Description: The phytoplankton of the Bahía Blanca Estuary, Argentina, has been surveyed since 1978. Chlorophyll a, phytoplankton abundance, species composition and physico-chemical variables have been fortnightly recorded. From 1978 to 2002, a single winter–early spring diatom bloom has dominated the main pattern of phytoplankton interannual variability. Such pattern showed noticeable changes since 2006: the absence of the typical winter bloom and changes in phenology, together with the replacement of the dominant blooming species, i.e. Thalassiosira curviseriata, and the appearance of different blooming species, i.e. Cyclotella sp. and Thalassiosira minima. The new pattern showed relatively short-lived diatom blooms that spread throughout the year. In addition, shifts in the phytoplankton size structure toward small-sized diatoms, including the replacement of relatively large Thalassiosira spp. by small Cyclotella species and Chaetoceros species have been noticed. The changes in the phenology and composition of the phytoplankton are mainly attributed to warmer winters and the extremely dry weather conditions evidenced in recent years in the Bahía Blanca area. Changing climate has modified the hydrological features in the inner part of the estuary (i.e. higher temperatures and salinities) and potentially triggered the reorganization of the phytoplankton community. This long-term study provides evidence on species-specific and structural changes at the bottom of the pelagic food web likely related to the recent hydroclimatic conditions in a temperature estuary of the southwestern Atlantic.

Description: Aurelia spp. is a cosmopolite scyphozoan species and likely the most studied jellyfish in the world. Its pelagic–benthic life cycle is complex, and the benthic asexual reproducing stage (polyp) is acknowledged fundamentally in bloom onset. Despite this, field investigations remain scarce and are mainly restrained to the western Pacific Ocean. Thau lagoon (43°23′59.10″ N 3°36′37.15″ E), a semi-enclosed system that harbours a resident population of Aurelia sp., is in essence a natural laboratory that offers an ideal framework to investigate the life cycle of the species. We here used a non-destructive approach consisting on a field survey over the entire lagoon (ca. 7 ha) and several substrate types by free diving to examine the distribution and habitat use of Aurelia sp. benthic population. We show that polyps were largely distributed over the entire lagoon, settled mainly on artificial hard substrates, thereby stressing the promoting role of anthropogenic perturbations in coastal areas, i.e. habitat modification, for jellyfish proliferations. Therefore, our study suggest a potential increase in Aurelia sp. benthic populations as an outcome of mounting coastal constructions in the near future; the consequences of which ultimately might promote an increase in jellyfish outbreaks.

Description: In aquatic ecosystems, body size has a remarkable influence on the hierarchical structure of food webs and trophic interactions. The trophic relationship between mosquito larvae and copepods offers an exception to the conspicuous feature that the bigger consumes the smaller. We here address this ecological question by investigating the predation impact of the epibenthic cyclopoid copepod Megacyclops formosanus on a 30-h old mosquito larvae Aedes aegypti in a controlled environment. Our quantitative assessment depicted the effect of M. formosanus on 30-h old mosquito larvae. We found that copepod captured mosquito larvae on an average 1.6 ± 0.20 larvae ind−1 h−1 with an attack speed 22.80 ± 8.52 mm s−1. In addition, copepod predation dramatically affected mosquito behavior. In the presence of predator, mosquito larvae significantly decreased browsing and filtering paths, while using mixed foraging tactics and shifting the habitat use from the bottom to surfacing or air–water interfacing. These results provide a mechanistic understanding of the interaction between mosquito and cyclopoid copepods, and show that copepod predation constrains the habitat use of mosquito larvae. Copepod predation pressure results in reduced facultative behavioral responses that challenge mosquito life history and ultimately percolate its population fitness.

Description: Spatial and temporal changes of the copepod community have been investigated and related to the environmental variability of the Balearic Sea (Western Mediterranean). The period studied spans from 1994 to 1999 during which we analyzed the abundance and structure copepod variability over a cross-shore transect. Results showed a close link between hydrological changes and the variations of copepod abundance. The synchronous variability of copepods and hydrography indicated the rapid response of this zooplankton group to the inflow of cold and warm water masses coming through the study area. Cluster analysis revealed four main copepod assemblages that distinguished the coastal from the oceanic species and those species with different water masses preference. The copepod assemblage composed of Calanus helgolandicus, Clausocalanus arcuicornis, C. pergens, C. paululus, Calocalanus tenuis and Pleuromamma gracilis was associated with cool salty waters, whereas the assemblage formed by Temora stylifera, C. pavo, C. styliremis, Centropages bradyi and Acartia danae was related to warmer less saline Mediterranean waters. Moreover, it is suggested that changes in sea water temperature and salinity are linked to large-scale changes likely occurring at a basin scale, which is reflected in the Western Mediterranean mesoscale hydrographic changes. Therefore, it is stressed that changes in the Balearic copepod community can be used as potential tracers of the western Mediterranean water masses

Description: We analyzed the seasonal variations of the ctenophore Mnemiopsis leidyi weekly collected since its first record in the western Baltic Sea in October 2006. The distribution pattern together with the seasonal dynamics and population outbreaks in late summer 2007 indicate recent successfully establishment of M. leidyi in this area. Seasonal changes showed two periods of high reproductive activity characterized by a population structure dominated by small size classes, followed by an increase of larger ones. These results further revealed that the bulk of the population remains in deep layers during the periods of low population density, whereas it appeared situated in upper layers during the proliferation of the species. We further emphasized the strength of the population outbreaks, which can reach abundances 〉10-fold higher in time periods shorter than a week. The predatory impact this species may have in pelagic ecosystems warns on the importance of its recent range of expansion.

Description: Ontogenetic changes in resource use are widespread in many fish species. This study investigated the feeding habits of whitefish (C. lavaretus L.) larvae in Lake Annecy (France) coupled with experimental behavioral studies in order to identify the underlying mechanisms of the ontogenetic shifts in the diet. The predatory behavior of wild larvae, and the escape responses of their zooplankton prey were both videorecorded in experimental tanks under controlled laboratory conditions. Ontogenetic diet patterns showed that young whitefish larvae have a preference for small cyclops, while older larvae selectively predate cladocerans. Our experimental observations showed that the capture success rate also varied in relation to ontogenetic development in fish. Young larvae were more successful in capturing small copepods, whereas old larvae were more successful in capturing Daphnia. In addition, the larvae were able to adjust their predatory behavior (speed, pursuit) according to the swimming pattern of the prey. These observations suggest that the selective predation on cladocerans observed in old larvae is the outcome of both active and passive choices depending on the escape swimming behavior of the prey, and handling time of the predator.

Description: The Mediterranean Sea is located in a crossroad of mid-latitude and subtropical climatic modes that enhance contrasting environmental conditions over both latitudinal and longitudinal ranges. Here, we show that the large-scale environmental forcing is reflected in the basin scale trends of the adult population of the calanoid copepod Centropages typicus. The species is distributed over the whole Mediterranean basin, and maximal abundances were found in the north-western basin associated to oceanic fronts, and in the Adriatic Sea associated to shallow and semi enclosed waters. The peak of main abundances of C. typicus correlates with the latitudinal temperature gradient and the highest seasonal abundances occurred in spring within the 14-18A degrees C temperature window. Such thermal cline may define the latitudinal geographic region where C. typicus seasonally dominates the > 200 mu m-sized spring copepod community in the Mediterranean Sea. The approach used here is generally applicable to investigate the large-scale spatial patterns of other planktonic organisms and to identify favourable environmental windows for population development.

Description: The biological pump describes the transport of particulate matter from the sea surface to the ocean's interior including the seabed. The contribution by gelatinous zooplankton bodies as particulate organic matter (POM) vectors ("jelly-falls") has been neglected owing to technical and spatiotemporal sampling limitations. Here, we assess the existing evidence on jelly-falls from early ocean observations to present times. The seasonality of jelly-falls indicates that they mostly occur after periods of strong upwelling and/or spring blooms in temperate/subpolar zones and during late spring/early summer. A conceptual model helps to define a jelly-fall based on empirical and field observations of biogeochemical and ecological processes. We then compile and discuss existing strategic and observational oceanographic techniques that could be implemented to further jelly-falls research. Seabed video- and photography-based studies deliver the best results, and the correct use of fishing techniques, such as trawling, could provide comprehensive regional datasets. We conclude by considering the possibility of increased gelatinous biomasses in the future ocean induced by upper ocean processes favouring their populations, thus increasing jelly-POM downward transport. We suggest that this could provide a "natural compensation" for predicted losses in pelagic POM with respect to fuelling benthic ecosystems.