The variability in abundance and shell size of the thecosome pteropods Limacina spp. in the seasonal ice zone of the Southern Ocean in March

Thecosome pteropods form an important part of marine food webs, especially in polar ecosystems, and are the focus of research on ocean acidification. Although the larval stages of species in the genus Limacina often form major components of zooplankton communities, little is known of their population dynamics. We report high Limacina spp. abundance in March 2000 during surface zooplankton community sampling via a Continuous Plankton Recorder (CPR; 270-µm mesh) in a large area within the seasonal ice zone of the Southern Ocean. Regions with high Limacina spp. abundances extended to 600 nautical miles ( ca 1110 km). Annual variability in Limacina spp. abundance and shell size is evaluated using North Pacific standard net (100-µm mesh) data from the same area and sampling periods (March) from 1997 to 2006. Although the relative total abundance of Limacina spp. in 2000 was the highest in the study period, its overall abundance was lower than the mean value for that period. Mean shell size for most years ranged 160–300 µm, while a relatively large mean size (444.7 µm) occurred in 2000. We conclude that a CPR with 270-µm mesh could catch large Limacina individuals that dominated in March 2000. The timing of reproduction and growth of the new generation may influence Limacina abundance throughout the sampling area.