Microzooplankton

Microzooplankton consist of heterotrophic organisms in the 20-200 μm size range including ciliates (naked, tintinnids), heterotrophic dinoflagellates, first larval stage of micrometazoans (e.g. copepod nauplia) and other protozoans (e.g. Foraminifera, Radiozoa). Microzooplankton organisms are considered one of the first links of the trophic system in consumer terms and, in Antarctica, they are an important food sources for krill and salps. A modification in their composition and quantity might trigger a cascade of short- and long-term changes in ecosystem structure and function, affecting both biodiversity and biogeochemical cycles in the pelagic system. Integrating the data we already have from the sea-ice (previous winter cruise) with the data obtained in the next cruise we will assess the importance of microzooplankton as food source for krill and salps in two different seasons. Microplankton (microphytoplankton and microzooplankton) that is not grazed in the ice, or at the ice water interface, is released into the water column, where it can be exploited by pelagic grazers or potentially seed the following microplankton growth. Although all the material incorporated in the ice matrix will ultimately be released into the water column during ice melt, and it is an important part of Antarctic biomass, little is known about its fate. Water and sediment samples will be analysed to assess the possible fate of sympagic organisms. Particular attention will be payed to foraminifera as they were one of the most abundant group present in the sea-ice during the winter cruise. Foraminifera is the only group among microzooplankton capable to secrete a calcareous test and they can be used as proxy for both past changes and surface ocean variations of sea-water conditions. In particular the study of foraminiferal biomass will be associated to the analyses of shell isotopic (d18O, d44Ca) and trace elements (Mg/Ca) to understand if the various environmental factors (namely [CO3 2–], temperature) passing from seasonal variations and ice to ice-free water, could affect foraminiferal biomineralization (and consequently biomass).