Staying out of the heat: how habitat use is determined by local temperature

Atlantic cod (Gadus morhua) and the Tvedestrand fjord on the Norwegian Skagerrak coast studied by Freitas et al. (). Photographs by Øystein Paulsen (left), and Institute of Marine Research, Norway (right). In Focus: Freitas, C., Olsen, E. M., Knutsen, H., Albretsen, J. & Moland, E. (2016) Temperature-associated habitat selection in a cold-water marine fish. Journal of Animal Ecology, 85, 611-613. In the marine environment, species distributions are closely linked to temperature gradients, but how individual behaviour is affected by local temperatures is less well understood. Freitas et al. () tracked Atlantic cod within a Norwegian fjord using electronic acoustic tags. They showed that when surface waters were warm, cod occupied the cold deep non-vegetated habitats. However, when surface waters cooled, fish moved into shallow seagrass and macroalgae beds that were previously out-of-bounds. The study provides a clear example of how thermal regimes determine habitat use over fine spatial and temporal scales, with potential implications for population dynamics under climate warming.