The importance of sea ice association of Antarctic krill for transport and retention in the South Orkneys region: a modelling study

The South Orkney Islands region is a key location for understanding the distribution of Antarctic krill in CCAMLR Area 48. The local krill populations support krill-dependent higher predators and krill fisheries, and the regional oceanographic circulation provides connections between the Antarctic Peninsula, the South Orkney Islands and the central Scotia Sea and South Georgia. Furthermore, the South Orkney Islands lie in the seasonal sea ice zone. Sea ice is an important overwintering habitat for Antarctic krill, and how krill use the sea ice habitat can impact their distribution. To better determine the local ecosystem dynamics in this key region requires greater understanding of the extent to which krill - sea ice interactions influence the local distribution and retention of krill. Here we present results from a modelling study that suggest that the use of the sea ice habitat by krill affects the regional and local transport pathways to and in the South Orkneys region, and the residence time of krill on the South Orkney plateau. We found that including sea ice-associated behaviour of krill in the model provides additional source regions for the South Orkney Islands krill population than when krill are advected only with ocean currents, permitting episodic transport from much of the northern Antarctic Peninsula within a 9 month time period. Sea ice-associated behaviour also reduces retention time on the South Orkney plateau, with sea ice transferring material off the shelf rapidly. Variability in the source regions and retention timescales arises from variability in the regional and local sea ice dynamics. Our results demonstrate the importance of understanding the behaviour of krill under sea ice, including how the behaviour changes in response to different sea ice conditions and as krill mature, to better resolve the connectivity of krill populations in CCAMLR Area 48.