Spatial and temporal patterns of Crassostrea virginica (Gmelin) recruitment: relationship to scale and substratum

Abstract

A series of experiments were performed in a euhaline (North Inlet, South Carolina) and mesohaline estuary (Wando River, South Carolina) to examine recruitment variability across several spatial and temporal scales. Crassostrea virginica (Gmelin) recruitment varied across all temporal and spatial scales with the exception of among reefs within restricted zones of the Wando River Estuary. Both biological and physical factors could be related to the variability observed at different scales. At the finest spatial scales, oyster larvae indicate a preference for crevices and shells or tests of other organisms as attachment sites. Higher recruitment on the shaded sides of plates in the high intertidal zone was consistent with observations documenting the preference of larvae for shaded attachment sites, adverse effects of direct exposure to light and heat, and sedimentation. Observations made at broader spatial scales (100s m) suggested that the availability of potential settlement surfaces may be the underlying factor contributing to the observed distribution of intertidal oyster reefs. Recruitment patterns were affected by choice and position of substrata. Sampling frequency was observed to influence the number of peak recruitment events observed within a season, estimates of total net recruitment, and the variability associated with recruitment observations made at different levels in the intertidal zone. Gregarious settlement behavior, sedimentation, and biophysical modification of the substrata were implicated in the regulation of recruitment patterns at shorter time scales. Competition and predation appeared to be important in regulating recruitment patterns at longer time scales, although the effects varied across the intertidal gradient. The physical and biotic processes which normally operate to structure intrareef spatial recruitment patterns were not observed to be as important in reefs which are physically restricted by tidal factors to very narrow zones within the intertidal gradient.