Temperature impacts on lipid allocation among juvenile gadid species at the Pacific Arctic-Boreal interface: an experimental laboratory approach

Climate change impacts on Arctic fish communities will largely be determined by temperature-dependent vital metabolic rates of resident and invading species. In this study, we experimentally measured total lipids and lipid class storage in the liver and muscle of 2 juvenile Arctic gadids (Arctic cod Boreogadus saida and saffron cod Eleginus gracilis) and 2 juvenile boreal gadids (walleye pollock Gadus chalcogrammus and Pacific cod Gadus macrocephalus). Experiments were conducted over a 4 wk period across 5 temperatures (0, 5, 9, 16 and 20 degrees C) at the Hatfield Marine Science Center in Newport, OR, USA. Results indicated clear species-specific non-linear effects of temperature on lipid accumulation. Arctic cod demonstrated a cold-water, stenothermic response with relatively high lipid storage (28 mg lipid g(-1) WWT) and growth at 0 degrees C. In contrast, saffron cod demonstrated a warmer-water, eurythermic response with elevated growth at temperatures beyond 16 degrees C but comparatively low lipid storage across all thermal habitats (10 to 17 mg lipid g(-1) WWT). Lipid storage and growth in the boreal species was dome-shaped and notably higher at intermediate temperatures (maximum lipid values of 44 mg lipid g(-1) WWT for walleye pollock, 28 mg lipid g(-1) WWT for Pacific cod). Further, the combined effects of temperature on both growth and lipid storage led to elevated lipid accumulation rate (LAR) indices in boreal species (4 to 11) compared to Arctic species (< 3) at temperatures above 4 degrees C. These results suggest that warming in the Arctic will lead to decreased condition in the resident mid-trophic fish assemblage in the absence of replacement by more boreal-type species shifting poleward.