Seasonal changes in the depth distribution of bivalve larvae on the Southern New England Shelf

A limited survey was made of the seasonal change in occurrence, depth distribution, size distribution, and species composition of bivalve larvae at a single station on the southern New England shelf during the period April-December 1981. The data were related to temperature structure of the water column and chlorophyll a distribution. Bivalve larvae were most abundant during late August and September at depths greater than 10 m, in water temperatures of 14 to 18°C, and chlorophyll a concentrations of200 p.m length consisted predominantly of the species Modiolus modiolus (Linne), Arctica islandica (Linne) and Spisula solidissima (Dillwyn). Modiolus modiolus was present in the depth range 10-40 m from late July through December with highest concentrations in August through October. Arctica islandica was present at I to 30m depth in May and from 20 to 40 m from late July through November. Larvae of A. islandica that were captured in May possibly originated from spawning in late 1980; those that were captured in November were first shelled veligers of 110 p.m length. Those larvae may form the basis of an overwintering larval population. Larvae of S. solidissima were present from late July through October and extended into shallower, warmer waters than larvae of either M. modiolus or A. islandica