Summary
Angus Atkinson will introduce the topic of Antarctic food webs, and show how rapid climate change in Antarctica is impacting this food web, causing range shifts and southwards shifts in the range of krill. He will focus particularly on the mechanisms behind the recent abrupt southwards range shift in krill, and its impacts on nutrient cycles, biogeochemical cycling and fisheries management. He will then take a wider, circumpolar, perspective to describe first, the potential for the Pacific- and Indian sectors to act as habitat refuges. Second, he will use their recent circumpolar comparative analysis of carbon biomasses of phytoplankton, mesozooplankton, krill and salps to illustrate the massive combined biomass of Southern Ocean zooplankton and how its role in the Biological Carbon Pump may change in a warmer world.
Top-down control on phytoplankton is considered to be rare in the SO, and if at all occurring, to be through microzooplankton rather than krill. Here Katrin Schmidt will show how some of krill’s life processes like strong vertical migration, the ingestion of lithogenic particles and the excretion of ammonium can reduce the iron stress for SO phytoplankton. If such activities are combined with a locally very high krill biomass, high feeding rates and spatial mobility, the species can play an important role in the fertilisation of SO phytoplankton. Such fertilising effects can be traced in situ using vertical profiles of krill density and nutrient concentrations, numerical budgets, and large-scale pattern in phytoplankton distribution during high and low krill years. The results indicate that we can’t understand and model SO nutrient cycles, primary production and carbon flux if large zooplankton such as krill are ignored.
Brief biography
Angus Atkinson joined Plymouth Marine Laboratory in 2012 from his previous employment (1984-2011) at the British Antarctic Survey. He is interested in all aspects of marine ecology and biogeochemistry, but with main focal areas on plankton and krill species, and particularly in polar regions and in the north Atlantic. Topics of particular interest include Euphausia superba (Antarctic krill); copepods; plankton size structure (biomass spectra); feeding ecology including selectivity; Antarctic, Arctic and north Atlantic food webs; iron cycling by zooplankton; climate warming responses including shifts in phenology, distributional range and body size; and pelagic-benthic coupling and the biological carbon pump.
Katrin Schmidt completed her PhD at the University of Rostock and worked since as a researcher at the Institute of Baltic Sea Research Warnemünde (Germany), the British Antarctic Survey and now at the University of Plymouth. Her studies address the role of zooplankton in marine food webs, in the biological carbon pump and in nutrient cycles. Of special interest are effects of climate change, i.e. the loss of sea ice in Polar Regions and increased stratification in temperate regions, on trophic relationships in the ocean. For her studies she uses various biomarker approaches, taxonomic analysis, long-term trends in phyto- and zooplankton, and the cooperation with oceanographers and biogeochemists.