Combining individual-based models and advection models to assess climate change impact on Antarctic krill

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The Southern Ocean is particularly susceptible to climate warming and comprises some of the most rapidly warming regions worldwide. This has resulted in an increase in sea surface temperatures of 0.9ºC in summer around the island of South Georgia since 1925 and 1ºC at the western Antarctic Peninsula from 1951 to 1998. Furthermore, global warming affects the extension of sea ice and the timing of sea ice formation. These environmental changes together with ocean acidification will impact the population dynamics of Antarctic krill (Euphausia superba) in an unknown way. Since krill is both an ecologically key species with its central role in the Antarctic food web and of high economic value, more reliable circumpolar projections of the trends of Antarctic krill populations in response to climate change are urgently needed for better management and conservation measures. In principle population models can provide such insights, but differing threats to, and behaviour of, larval krill compared with adult krill means that mechanistic models are needed instead of correlative empirical models. It will be crucial to consider the behaviour and individual variability of krill in the model to assess the adaptation potential of krill to global change. Therefore, individual-based, process-based models will be designed and implemented including physiological submodels for different life stages of krill. Modelling the whole life cycle of krill is particularly important since krill reverses its daily vertical migration behaviour as it gets older and while adult krill is able to reduce its metabolic activity in winter larval krill has to remain active throughout the year. Apart from physiological and behavioural aspects it is crucial to understand to which environmental conditions krill is exposed to. Especially sea ice cover is supposed to play a crucial role since it provides krill larvae shelter from predators and currents, but is also a low food environment where resources are scarce and patchily distributed. To meaningfully investigate the impact of changing spatial and temporal sea ice dynamics and food availability on the krill population dynamics the individual based model needs to be coupled with advection models. This is especially important as krill larvae do not actively swim and their interaction with sea ice can have a significant impact on their transport in terms of destination and timing of arrival. The coupling of advection models and individual-based models is highly innovative requiring appropriate handling of the different spatial and temporal resolutions relevant for the two modelling components, namely the krill and its transport by water currents and sea ice drift. The proposed project will thus help to integrate existing knowledge, allowing for an improved projection of the likely impact of environmental change on Antarctic krill at circumpolar scales.