Pteropod time-series from the NE Pacific

Pteropods are marine planktonic molluscs that play important roles as broad-spectrum microplankton grazers, and as prey for fish, squid, and other plankton. Most species (e. g. Limacina, Clio) form aragonite shells. Others (e.g. Clione) lack shells as adults but are narrow-spectrum predators that rely on shelled pteropods as their primary or exclusive prey. The entire group is therefore potentially threatened by increasing ocean acidification, which in some regions (including the NE Pacific) is now approaching the solubility threshold for aragonite. Despite the grounds for ecological concern, there are few long-term time-series of pteropod populations. Time-series of pteropod biomass anomalies off the Vancouver Island continental margin and in the eastern Alaska Gyre (Line P) are analysed. Off both southern and northern Vancouver Island, Limacina (the dominant Subarctic thecate pteropod) has declined notably. Continental margin trends for Clione (the dominant athecate) are mostly positive but not significant. Occurrence rate and quantity of Clio (a subtropical species) have increased greatly. The shorter (13-14 year) Line P time-series as yet shows no overall trends for any of the species, although there are positive annual anomalies of Clio in the same years in both continental margin and oceanic regions.