ALBERT

Description: Food chains in the pelagic zones of oceans and lakes are longer than in terrestrial ecosystems. The perception of the pelagic food web has become increasingly complex by progressing from a linear food chain (phytoplankton – crustacean zooplankton – planktivorous fish – predatory fish) to a food web because of an increasing appreciation of microbial trophic pathways, side-tracks by gelatinous zooplankton and a high prevalence of omnivory. The range of predator:prey size ratios by far exceeds the traditionally assumed range of 10:1 to 100:1, from almost equal length to 105:1. The size ratios between primary consumers and top predators are 3½ orders of magnitude bigger in pelagic than in terrestrial food webs. Comparisons between different pelagic ecosystems support ecosystem size as an important factor regulating the maximal trophic level, while energy limitation of the number of trophic levels is less well supported. An almost 1:1 relationship between ingestion by predators and prey mortality and a better chemical match between primary producer and herbivore biomass are further distinctive features of the pelagic food web whose role in explaining the higher number of trophic levels in pelagic systems needs further examination.

Description: Anthropic activities impact ecosystems worldwide thus contributing to the rapid erosion of biodiversity. The failure of traditional strategies targeting single species highlighted ecosystems as the most suitable scale to plan biodiversity management. Network analysis represents an ideal tool to model interactions in ecosystems and centrality indices have been extensively applied to quantify the structural and functional importance of species in food webs. However, many network studies fail in deciphering the ecological mechanisms that lead some species to occupy the most central positions in food webs. To address this question, we built a high-resolution food web of the Gulf of California and quantified species position using 15 centrality indices and the trophic level. We then modelled the values of each index as a function of traits and other attributes (e.g., habitat). We found that body size and mobility are the best predictors of indices that characterize species importance at local, meso- and global scale, especially in presence of data accounting for energy direction. This result extends previous findings that illustrated how a restricted set of traitaxes can predict whether two species interact in food webs. In particular, we show that traits can also help understanding the way species are affected by and mediate indirect effects. The traits allow focusing on the processes that shape the food web, rather than providing case-specific indications as the taxonomy-based approach. We suggest that future network studies should consider the traits to explicitly identify the causal relationships that link anthropic impacts to role changes of species in food webs.

Description: This first “World Ocean Review” is published in 2010 and will be followed by periodic updates in the future. The result is a comprehensive, detailed and unique report about the state of the world’s oceans and their interplay with ecological, economic and sociopolitical conditions. Its aim is to increase public awareness of the interconnected nature of the diverse aspects of the marine environment and thus to boost marine conservation.

Description: Der „World Ocean Review" erscheint 2010 das erste Mal und soll in Zukunft in regelmäßigen Abständen herausgegeben werden. Entstanden ist ein umfassender und profunder Bericht, der den Zustand der Weltmeere und die Wirkungszusammenhänge zwischen dem Ozean und ökologischen, ökonomischen und gesellschaftspolitischen Bedingungen aufzeigt. Die wissenschaftlich gesicherten Erkenntnisse sollen all denen dienen, die sich aktiv und fundiert an den aktuellen Diskussionen im Umfeld der Meeresforschung beteiligen möchten.

Description: We investigated the impacts of predicted ocean acidification and future warming on the quantity and nutritional quality of a natural phytoplankton autumn bloom in a mesocosm experiment. Since the effects of CO2-enrichment and temperature have usually been studied independently, we were also interested in the interactive effects of both aspects of climate change. Therefore, we used a factorial design with two temperature and two acidification levels in a mesocosm experiment with a Baltic Sea phytoplankton community. Our results show a significant time-dependent influence of warming on phytoplankton carbon, chlorophyll a as well as POC. Phytoplankton carbon for instance decreased by more than a half with increasing temperature at bloom time. Additionally, elemental carbon to phosphorus ratios (C:P) increased significantly by approximately 5-8 % under warming. Impacts of CO2 or synergetic effects of warming and acidification could not be detected. We suggest that temperature-induced stronger grazing pressure was responsible for the significant decline in phytoplankton biomass. Our results suggest that biological effects of warming on Baltic Sea phytoplankton are considerable and will likely have fundamental consequences for the trophic transfer in the pelagic food-web.

Description: Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1-5) and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA) and arachidonic acid (ARA) to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts