Abstract
Competency to settle in larvae of the oyster Crassostrea virginica is defined as proportional settlement of a given number of larvae within 24 h. It is distinguished from apparent competency, which is based on observed morphological characteristics. Competency of pediveliger larvae in lower York River, Chesapeake Bay, Virginia (taken by plankton pump from near the bottom of the water column) was 81.1% in 1990, and 79.9% in 1992. Larvae taken from midwater samples and near-surface samples showed a competency of 70.0 and 58.9%, respectively, but these values were not significantly different from the 1992 near-bottom samples. There were no handling effects, or larval density effects, on competency, based on assays using hatchery-reared larvae. Settlement over three trials of hatchery-reared larvae ranged from about 7% to 32% in 24 h. These percentages are much lower than those for York River larvae, but similar to daily settlement reported by commercial oyster hatcheries elsewhere.
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