Modelling Calanus population dynamics under climate change along the North American Pacific margin from the California Current to the Arctic

Neil Banas, University of Strathclyde, Glasgow, United Kingdom, Aidan Hunter, University of Strathclyde, Mathematics and Statistics, United Kingdom, Carin J Ashjian, Woods Hole Oceaonographic Institution, Woods Hole, MA, United States, Julie E Keister, University of Washington, School of Oceanography, Seattle, WA, United States, Robert G Campbell, University of Rhode Island Narragansett Bay, Narragansett, RI, United States, David G Kimmel, NOAA Fisheries, Alaska Fisheries Science Center, Seattle, WA, United States, Lisa B Eisner, NOAA - Alaska Fisheries Science Center, Seattle, United States, Sofia Araujo Ferreira, University of Oslo, CEES / Department of Biosciences, Oslo, Norway and Jinlun Zhang, University of Washington, Seattle, WA, United States
Abstract:
Overlapping populations of Calanus marshallae and C. glacialis are crucial components of the mesozooplankton community along the Pacific margin of North America from the northern California Current to the high Arctic. It has long been unclear whether observed differences in size, phenology, life history, and behaviour among these populations are inherent and fixed, or plastic, emergent responses to environmental gradients, and this uncertainty leads to further uncertainty in the adaptive capacity of the Calanus metapopulation under climate change. An individual-based model for Calanus spp. (Coltrane, http://neilbanas.com/projects/coltrane) was jointly tuned to observations of body size and interannual abundance variation at station M2 (Southeastern Bering Sea) and the Newport Line (Northern California Current). A hierarchical cost function, evaluated through multi-stage particle-swarm optimisation, allowed model parameters such as ingestion and development rates to differ between the Bering and Newport populations, but the results do not allow one to reject the hypothesis that the two populations have identical functional traits. A spatial version of the model was run for the Bering-Chukchi-Beaufort shelf along particle tracks generated from the three-dimensional, biophysical BIOMAS model. A Calanus metapopulation with identical functional traits shows an emergent shift from a one-year to a two-year life cycle, near the break between the Chukchi shelf and the central Arctic basin, consistent with ship-based observations of stage structure from winter 2011 and spring 2014. The model also suggests a strong but incomplete population bottleneck that restricts the flux of successful individuals from the Bering Sea onto the Chukchi shelf and beyond, and keeps the reproductive capacity of the individuals that do pass through below replacement rate. This bottleneck, which is consistent with past mapping of C. glacialis population genetics, appears to be stronger in warmer, lower-ice conditions. Backtracking in the spatial model links interannual changes in autumn Calanus abundance on the Bering shelf both to changes in spring/summer growth conditions and to variation in advective origins.
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