Modelling the effects of changes in sea-ice extent on Arctic marine food webs

Heath, Michael and Benkort, Deborah and Brierley, Andrew and Daewel, Ute and Hofmeister, Richard and Proud, Roland and Schrum, Corinna and Speirs, Douglas (2018) Modelling the effects of changes in sea-ice extent on Arctic marine food webs. In: MASTS Annual Science Conference, 2018-10-31 - 2018-11-01, Technology & Innovation Centre (TiC).

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Diminishing extent of sea-ice cover in the Arctic over recent decades is well documented, and linked to global warming. The ecological effects have been profound especially in areas which have transformed from extensive seasonal ice-cover, to marginal sea-ice or year-round open water. The effects include an increase in Arctic primary production and changes in habitat and food availability for iconic marine mammals. Fishing nations anticipate increased harvesting opportunities in the Arctic as ice cover retreats further, but in November 2017 an international agreement was reached to prevent fisheries development in the Central Arctic Ocean for at least the next 16 years, to give time for development of scientific understanding. The scope for changes primary production due to diminishing sea-ice to propagate through the food web and affect higher trophic levels and charismatic megafauna such as whales, seals and polar bears, is extremely uncertain and hard to predict. The classical hypothesis would be that warming climate will result in a bottom-up trophic cascade from a) increased primary production, to b) increased zooplankton production, to c) increased fish production and harvesting potential, through to d) increased populations of charismatic marine megafauna. However, this assumes that primary production is retained in the upper layers of the water column – the outcome could be quite different if changes in vertical mixing and animal behavior associated with loss of ice cover lead instead to a greater proportion of primary production being directed to the benthos. Here we report on results from a configuration of the StrathE2E marine food web model to represent the Barents Sea. First, we show a baseline model representing sea-ice and temperature conditions during the 1980s-1990s, and then compare this with results from simulation of a warmer, year-round ice-free scenario. The results show that the increase in primary production in the ice-free scenario is amplified as it cascades up the food web. The effects preferentially benefit benthos and demersal fish, but this result is sensitive assumptions about prey preferences and vertical mixing. We also show how the food web responds to harvesting of fish, under both contemporary ice-cover and future ice-free situations. The results presented here are a starting point for a much more extensive new project under the NERC Charging Arctic Ocean Programme (Microbes to Megafauna Modelling of Arctic Seas (MiMeMo)) which we briefly introduce.