Evaluating temperature as a driver of changing coastal biodiversity

Coastal waters are warming for many regions of the world, but the impacts on biodiversity are unclear. Theoretical mechanisms for temperature-driven changes in diversity include the expansion of highly diverse warm-water communities, and a tendency for colonizations to occur more rapidly than extinctions. However, these hypotheses remain untested. In fact, some surveys of biodiversity indicate no systematic change in local species richness for most regions of the world.

We evaluated the empirical evidence for these proposed mechanisms using long-term and spatially extensive surveys in conjunction with statistical methods robust to observational biases. In contrast to other empirical studies, we identified consistent increases in the richness of North American demersal communities in recent decades. The changes in these communities are associated with changing water temperatures, but are not well-predicted by proposed mechanisms. Most theoretical expectations for how temperature may change biodiversity involve biogeographic dynamics. By determining the timing and locations of colonization and extinction events of ~2000 species, we provide a rare assessment of the merits and shortcomings of these hypotheses as they pertain to observed changes coastal biodiversity.