Ocean acidification affects the phyto-zoo plankton trophic transfer efficiency

The critical role played by copepods in ocean ecology and biogeochemistry warrants an understanding of how these animals may respond to ocean acidification (OA). Whilst an appreciation of the potential direct effects of OA, due to elevated pCO2, on copepods is improving, little is known about the indirect impacts acting via bottom-up(food quality) effects. We assessed, for the first time, the chronic effects of direct and/or indirect exposures to elevated pCO2 on the behaviour, vital rates, chemical and biochemical stoichiometry of the calanoid copepod Acartia tonsa. Bottom-up effects of elevated pCO2 caused species-specific biochemical changes to the phytoplanktonic feed, which adversely affected copepod population structure and decreased recruitment by 30 %. The direct impact of elevated pCO2 caused gender-specific respiratory responses in A.tonsa adults, stimulating an enhanced respiration rate in males (> 2-fold), and a suppressed respiratory response in females when coupled with indirect elevated pCO2 exposures. Under the combined indirect+direct exposure, carbon trophic transfer efficiency from phytoplankton-to-zooplankton declined to < 50 % of control populations, with a commensurate decrease in recruitment. For the first time an explicit role was demonstrated for biochemical stoichiometry in shaping copepod trophic dynamics. The altered biochemical composition of the CO2-exposed prey affected the biochemical stoichiometry of the copepods, which could have ramifications for production of higher tropic levels, notably fisheries. Our work indicates that the control of phytoplankton and the support of higher trophic levels involving copepods have clear potential to be adversely affected under future OA scenarios.

Concentrations of heavy and precious metals in animals from hydrothermal vents of the Axial Seamount (Juan de Fuca Ridge) and Guaymas Basin (Gulf of California)

A series of samples of inhabitants of hydrothermal vents were collected during the 12-th cruise of R/V Akademik Mstislav Keldysh in Guaymas Basin (the Gulf of California) and the Axial Seamount area (Juan de Fuca Ridge). Concentrations of trace and heavy metals in the tissues of Ridgeia piscesae, Riftia pachyptila, and Paralvinella palmiformis were analyzed. Neutron-activation analysis revealed significantly higher concentrations of uranium in tissues of Paralvinella palmiformis as compared to ambient seawater. Possible reasons for such phenomenon are discussed. The data obtained by neutron-activation method are compared with those obtained by atomic-absorption method for the same tissues analyzed.

d15N of lipids in marine animals of the Dutch Wadden Sea

Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (d15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the d15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the d15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in d15N of biomass (differences ranging from -2.3 to +1.8 per mil). Importantly, the total lipid extract (TLE) was highly depleted in 15N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 per mil). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, the d15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine d15N values differed by -7 to +2 per mil from bulk biomass d15N, and correlated well with the 15N depletion in TLEs. On average, serine was less depleted (-3 per mil) than the TLE (-7 per mil), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in 15N of the TLE relative to biomass increased with the trophic level of the organisms.

(Table 2) Abundance of the main groups of planktonic animals in the 250-900 m water layer at the Broken Spur and Lost City sites according to visual counts from the Mir manned submersibles in 2002 and 2005

Three dives of the Mir manned submersibles with plankton counts and two vertical plankton hauls with a BR net were carried out above the Lost City (Atlantis underwater massif) and the Broken Spur hydrothermal fields during cruise 50 of R/V Akademik Mstislav Keldysh. Above the Atlantis seamount no significant increase in plankton concentration was found. Above the Lost City field horizontal heterogeneity of plankton distribution in the near-bottom layer and in overlying water layers was shown. Near-bottom aggregations of euphausiids and amphipods previously reported by other scientists seem to be related to attraction of these animals by the submersible's headlights rather than represent a natural phenomenon.

(Table A1) Annual biomass of plants and animals recorded on Bylot Island between 1993-2009

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator--rey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of allochthonous resources subsidizing top predators and the absence of large herbivores may partly explain the predominant role of predation in this low-productivity ecosystem.