Species variability and population structure of Euphausiacea in Admiralty Bay (King George Island; South Shetland Islands) during Antarctic summer

The main component of zooplankton in Antarctic pelagic waters, apart from copepods or salps, are specimens representing euphausiids. In fjordic areas like Admiralty Bay, data concerning krill is still scarce and fragmentary, despite the fact that those organisms are a significant element of the penguins and pinnipeds’ diet. Admiralty Bay, because of its specific hydrological conditions, is an interesting area for that kind of biological study. Moreover, King George Island, where Admiralty Bay is located, is a region of dynamic climate characterized by variable maritime conditions which make this region particularly susceptible to climate change. This area is also a breeding site of the three Pygoscelis penguin species.  The data presented here is based on samples collected during an expedition to the H. Arctowski station in the Antarctic summer 2008-2009. Biological materials were collected in the central part of Admiralty Bay, in Ezcurra Inlet and in the smaller coves of the bay using the WP2 net with a mesh size of 200 µm. Studies showed that krill was represented by species such as Euphausia superba, E. frigida, E. crystallorophias and Thysanoessa macrura. Th. macrura, compared for example to E. superba, occurred in higher numbers in Admiralty Bay and was recorded at all stations. As a result, population structure analyses were possible only for the Th. macrura individuals. The data also showed how important it is to conduct more regular analyzes in such Antarctic areas which could demonstrate more pronounced trends.