MEPS 182:175-185 (1999)  -  doi:10.3354/meps182175

ABSTRACT: We sampled the early drifting post-larvae of a complex of 2 species of tellinid bivalves, Macoma spp., at a station in the lower York River, Chesapeake Bay, USA. Plankton samples were collected by pump every 3 h from 3 depths (surface, mid-depth, and bottom) on 4 dates corresponding to full and new moons. Macoma spp. post-larvae (size range 400 to 500 µm) were abundant in the plankton throughout the sampling period. The environmental factors influencing the abundance and vertical distribution of drifting post-larvae were evaluated using linear and logistic regression. Post-larvae were always more abundant during night as compared to day and were more abundant during nocturnal, flooding tides than during ebbing tides. In general, they were closer to the surface at night and during flood tides, though these patterns were highly variable. These data indicate that drifting post-larval bivalves use 'selective tidal stream transport' to promote upstream dispersal as observed in the post-larvae of other estuarine taxa (e.g. crabs and fish). The post-larval stage generally re-invades juvenile habitats following the export of larvae to the mouth of the parent estuary or nearshore continental shelf. We suggest that small drifting post-larval bivalves exert behavioral control over suspension in the water column. This life-history stage serves to maintain high densities of juveniles and adults in the upstream portions of the York River estuary despite downstream transport of early larval stages.

KEY WORDS: Post-larval bivalves · Thread drifting · Tidal stream transport · Macoma spp.