Warming oceans will reshape marine body sizes in surprising and uneven ways

A new analysis of more than 23,000 marine mollusk species challenges the long-held “temperature-size rule” that predicts warming oceans will make animals shrink. The study, published August 31 in the Proceedings of the National Academy of Sciences, was led by Isaac Trindade-Santos with Craig McClain and projects body-size changes through 2100 across 10 major ocean basins under high- and low-emissions scenarios. Using 2.79 million species occurrence records and measurements across five mollusk groups, the researchers found declines in mean body size across about two-thirds of region-and-group combinations under high emissions—dropping by 16% in extreme cases. But results also show growth: Arctic cephalopods and tusk shells are projected to increase by 2.9% and 3.3%.