ABSTRACT:

Climate regime shifts force fish communities through rapid transitions between alternate species assemblages, but little is known about the role that biochemical ecology plays in these transitions. We document a biochemical effect of climate-induced community transitions in boreal oceans: opposite population trajectories of lipid-rich and lipid-poor fish species. We compared published estimates of fish lipid content and population trajectories following climate shifts in 4 areas (Bering Sea, Gulf of Alaska, Scotian Shelf and North Sea). In all cases, total lipid content differed between species that increased and decreased in abundance, and the resulting relatively lipid-rich or lipid-poor communities persisted for decades. We hypothesize that these changes in fish community lipid content are the result of climate-mediated changes in the availability of essential fatty acids (EFAs), which are required by fish as components of hormones and cell membranes. EFAs are produced only by plants and must be obtained by fish through their diet, and ecosystem EFA availability is sensitive to physical forcing mechanisms. Using original data from 5 species of northeast Pacific fish (total lipid 1.0 to 28.9% wet mass) and published data for 29 species of myctophids (total lipid 0.5 to 46.3% wet mass), we found that the content of 2 important EFAs was positively correlated with total lipid content. This result suggests the possibility of species differences in EFA requirements that are related to total lipid content, and possible differences in susceptibility to changing EFA availability in lipid-rich and lipid-poor fish species.