Description: The increasing CO2 concentration in the atmosphere caused by burning fossil fuels leads to increasing pCO2 and decreasing pH in the world ocean. These changes may have severe consequences for marine biota, especially in cold-water ecosystems due to higher solubility of CO2. However, studies on the response of mesozooplankton communities to elevated CO2 are still lacking. In order to test whether abundance and taxonomic composition change with pCO2, we have sampled nine mesocosms, which were deployed in Kongsfjorden, an Arctic fjord at Svalbard, and were adjusted to eight CO2 concentrations, initially ranging from 185 µatm to 1420 µatm. Vertical net hauls were taken weekly over about one month with an Apstein net (55 µm mesh size) in all mesocosms and the surrounding fjord. In addition, sediment trap samples, taken every second day in the mesocosms, were analysed to account for losses due to vertical migration and mortality. The taxonomic analysis revealed that meroplanktonic larvae (Cirripedia, Polychaeta, Bivalvia, Gastropoda, and Decapoda) dominated in the mesocosms while copepods (Calanus spp., Oithona similis, Acartia longiremis and Microsetella norvegica) were found in lower abundances. In the fjord copepods prevailed for most of our study. With time, abundance and taxonomic composition developed similarly in all mesocosms and the pCO2 had no significant effect on the overall community structure. Also, we did not find significant relationships between the pCO2 level and the abundance of single taxa. Changes in heterogeneous communities are, however, difficult to detect, and the exposure to elevated pCO2 was relatively short. We therefore suggest that future mesocosm experiments should be run for longer periods.

Description: The increasing CO2 concentration in the atmosphere caused by burning fossil fuels leads to increasing pCO2 and decreasing pH in the world ocean. These changes may have severe consequences for marine biota, especially in cold-water ecosystems due to higher solubility of CO2. However, studies on the response of mesozooplankton communities to elevated CO2 are still lacking. In order to test whether abundance and taxonomic composition change with pCO2, we have sampled nine mesocosms, which were deployed in Kongsfjorden, an Arctic fjord at Svalbard, and were adjusted to eight CO2 concentrations, initially ranging from 185 μatm to 1420 μatm. Vertical net hauls were taken weekly over about one month with an Apstein net (55 μm mesh size) in all mesocosms and the surrounding fjord. In addition, sediment trap samples, taken every second day in the mesocosms, were analysed to account for losses due to vertical migration and mortality. The taxonomic analysis revealed that meroplanktonic larvae (Cirripedia, Polychaeta, Bivalvia, Gastropoda and Decapoda) dominated in the mesocosms while copepods (Calanus spp., Oithona similis, Acartia longiremis and Microsetella norvegica) were found in lower abundances. In the fjord copepods prevailed for most of our study. With time, abundance and taxonomic composition developed similarly in all mesocosms and the pCO2 had no significant effect on the overall community structure. Also, we did not find significant relationships between the pCO2 level and the abundance of single taxa. Changes in heterogeneous communities are, however, difficult to detect, and the exposure to elevated pCO2 was relatively short. We therefore suggest that future mesocosm experiments should be run for longer periods.

Description: In 2009 scientists at the Alfred Wegener Institute (AWI) Helmholtz Centre of Polar and Marine Research in Bremerhaven established the PEBCAO-group. Since then the group is investigating the “Plankton Ecology and Biogeochemistry in the Changing Arctic Ocean” in a uniquely synchronized approach. This involves the integration of molecular genetic investigations with traditional plankton investigations, optical parameters, microbiology, work on key species (e.g. Phaeocystis sp. or Calanus sp.), and finally the composition of organic matter. The work is carried out in the Central Arctic Ocean and the Fram Strait, where it is complementing a monitoring program on phytoplankton and vertical particle flux that has been carried out along ~79°N and in the AWI HAUSGARTEN for more than ten years. This is done in cooperation with oceanographers and deep-sea biologists. Combining the long-term data (1998-2012) with the integrative approach of PEBCAO we revealed a trend towards slightly higher chlorophyll a in the WSC during summer that is accompanied by a shift from diatoms to Phaeocystis sp. and other small pico- and nanoplankton. Furthermore, a clear zonation in the waters of the East Greenland Current (EGC), the West Spitsbergen Current (WSC) as well as for the mixing zone of both (MW) was identified in all parameters. The PEBCAO approach is an example for a successful and synergistic integration of molecular biodiversity studies with classical approaches of biological oceanography.

Description: High latitude marine ecosystems experience strong seasonality in incoming light and thus food availability. The ongoing reduction in sea ice thickness and extent will change the underwater light climate significantly in the Arctic. Herbivorous calanoid copepods of the genus Calanus of northern higher latitudes are considered to endure times of unfavorable environmental conditions in a state of arrested development, referred to as diapause. However, to date we have very limited knowledge regarding the overwintering physiology and adaptability of Calanus spp. to changes in external cues like light and food. To study potential impacts of changes in the light and primary production regime on Calanus spp. in the Arctic, we measured enzymatic response and biochemical composition of Calanus glacialis copepodite stage V to presence or absence of food (Thalassiosira spp.) and light in winter (November 2009) and summer (July 2010). In situ proteinase and lipase/esterase activity was 10 times and 19 times higher, respectively, while metabolic activity (citrate synthase, CS) was twice as high for C. glacialis CV in summer compared to winter, suggesting that individuals collected at depth in winter had reduced activity and were in an overwintering state. Food availability amplified digestive activity in both seasons, while light had a minor effect in comparison. In winter, gel electrophoresis revealed a change in enzyme pattern over the three weeks of incubation, indicating that feeding induced enzyme expression. Green guts in approximately 90% of fed individuals at the end of the experiment supported that they were actively feeding. However, there was no significant increase in dry mass or carbon and nitrogen content in feeding individuals during the winter experiment. These results suggest that factors other than food and light must be involved in controlling the transition from diapauses to activity in C. glacialis, which is currently under investigation. Understanding the consequences of shifting environmental parameters on the physiology of this energy rich copepod species is crucial to assess to the survival success of the overwintering stock and therefore the fate of the pelagic food web and especially of higher trophic levels in the following spring.

Description: In the Polar Regions, sea ice habitats are undergoing rapid environmental change. Because sea ice constitutes an important substrate for numerous species, as well as an important carbon source during critical periods of the year, these changes have a significant impact on ecosystem functioning, biodiversity, species distribution, and population sizes of both commercially exploited species, and species valuable from a conservation perspective. Species dwelling at the ice-water interface (e.g. Antarctic krill Euphausia superba and Arctic cod Boreogadus saida) are assumed to play key roles in these ecosystems. As an important trophic carbon transmitter from the sea ice into pelagic food webs and ultimately to the deep sea benthos, under-ice fauna can contribute significantly to the carbon flux in polar ecosystems. Whether the function of Arctic and Antarctic under-ice communities as trophic carbon transmitters is comparable in spite of great differences in the environmental regimes of the two Polar Oceans, however, is an open question. Quantifying under-ice communities was hampered in the past by the inaccessibility of the ice underside to conventional sampling gear. Using a new under-ice trawl, it was demonstrated that Antarctic krill concentrates under sea ice almost year-round, and that krill dwelling under ice are often under-estimated by pelagic nets and sonars. A diverse suite of species, including copepods, amphipods and pteropods, shares this attraction to the Antarctic ice underside at least temporarily. An Arctic expedition in 2012 using an improved version of this sampling gear brought evidence of a similarly rich under-ice community even in the biologically poor-considered central Arctic Ocean. Using a bio-environmental sensor array during under-ice fishing enabled fine-scale characterization of sea ice habitat properties as a basis for statistical modeling of under-ice species distribution. In the Arctic sea ice system, the trophic role that in the Southern Ocean is attributed to Antarctic krill may be resembled by the ice amphipod Apherusa glacialis (as a consumer of ice algae), and Arctic cod (as a key prey of top predators). This talk will evaluate published and unpublished results from under-ice fishing in the Southern Ocean in comparison to recent findings from the Arctic Ocean. With the availability of two unique datasets from oceanic sea ice systems in both Polar Oceans, similarities and differences between their under-ice communities will be highlighted, and hypotheses on the future fate of sea ice ecosystems will be discussed.

Description: Recent studies on the impacts of ocean acidification on pelagic communities have identified changes in carbon to nutrient dynamics with related shifts in elemental stoichiometry. In principle, mesocosm experiments provide the opportunity of determining temporal dynamics of all relevant carbon and nutrient pools and, thus, calculating elemental budgets. In practice, attempts to budget mesocosm enclosures are often hampered by uncertainties in some of the measured pools and fluxes, in particular due to uncertainties in constraining air–sea gas exchange, particle sinking, and wall growth. In an Arctic mesocosm study on ocean acidification applying KOSMOS (Kiel Off-Shore Mesocosms for future Ocean Simulation), all relevant element pools and fluxes of carbon, nitrogen and phosphorus were measured, using an improved experimental design intended to narrow down the mentioned uncertainties. Water-column concentrations of particulate and dissolved organic and inorganic matter were determined daily. New approaches for quantitative estimates of material sinking to the bottom of the mesocosms and gas exchange in 48 h temporal resolution as well as estimates of wall growth were developed to close the gaps in element budgets. However, losses elements from the budgets into a sum of insufficiently determined pools were detected, and are principally unavoidable in mesocosm investigation. The comparison of variability patterns of all single measured datasets revealed analytic precision to be the main issue in determination of budgets. Uncertainties in dissolved organic carbon (DOC), nitrogen (DON) and particulate organic phosphorus (POP) were much higher than the summed error in determination of the same elements in all other pools. With estimates provided for all other major elemental pools, mass balance calculations could be used to infer the temporal development of DOC, DON and POP pools. Future elevated pCO2 was found to enhance net autotrophic community carbon uptake in two of the three experimental phases but did not significantly affect particle elemental composition. Enhanced carbon consumption appears to result in accumulation of dissolved organic carbon under nutrient-recycling summer conditions. This carbon overconsumption effect becomes evident from mass balance calculations, but was too small to be resolved by direct measurements of dissolved organic matter. Faster nutrient uptake by comparatively small algae at high CO2 after nutrient addition resulted in reduced production rates under future ocean CO2 conditions at the end of the experiment. This CO2 mediated shift towards smaller phytoplankton and enhanced cycling of dissolved matter restricted the development of larger phytoplankton, thus pushing the system towards a retention type food chain with overall negative effects on export potential.