Growth cycle and related vertical distribution of the thecosomatous pteropod Spiratella (“Limacina”) helicina in the central Arctic Ocean

The growth cycle and related vertical distribution of the thecosomatous pteropod Spiratella (“Limacina”) helicina (Phipps) were studied. S. helicina has a life cycle of approximately 1.5 to 2 years in the central Arctic Ocean (Canada Basin). It spawns mainly during the spring to summer period, and on a small scale during the winter. The young double their sizes during the winter months of October to May, slow down in growth until late summer, and attain maximum size in early winter. The oldest disappear by late March. Gonadal tissue was first seen in young pteropods of 0.7 mm diameter, the predominant size from February to April. S. helicina 0.8 mm in diameter, the size predominant from May through July, are mature and hermaphroditic. Growth during the winter months suggests that particulate organic matter is available during this period to these obligate ciliary feeders. Vertical distribution is size and season-dependent. The youngest specimens collected (0.2 to 0.4 mm) were found concentrated in the first 50 m. The larger sizes dispersed during the summer months, and tended to concentrate in the top 150 m during the rest of the year. They aggregated in the top 50 m from late winter through early spring, and fall through early winter; then concentrated in the 100 to 50 m level until the end of winter. Numerous environmental factors seem to be involved in determining the vertical distribution of the species in the central Arctic Ocean.