Long-Term Faunal Changes in California Nudibranchs: Climate Change and Local Ocean Health

This project has established the feasibility of using intertidal nudibranchs (brightly colored, shellless mollusks) as fine-scale indicators of basin-scale climate variability and its effects on California’s coastal ecology locally. Among the project’s findings, total nudibranch abundance was highly correlated with warming—i.e., El Niño events, elevated sea surface height and temperature, and the warm phase of the Pacific Decadal Oscillation (PDO). It was negatively correlated with La Niña events, the cold phase of the PDO, enhanced coastal upwelling and the “positive” phase of the North Pacific Gyre Oscillation. Superimposed on this variability, biologists also documented a northward range expansion of one species of nudibranch, consistent with global-warming trends. In terms of the work’s applicability to management, nudibranch populations on rocky intertidal habitats (some of which are already currently being monitored) could be included in population dynamics models of species with long pelagic larval periods, notably the commercially important red sea urchin. The larger, more conspicuous nudibranch species would be appropriate for monitoring by biologists and citizen scientists, especially in marine protected areas.