Gregarious Setting in the American Oyster Crassostrea virginica Gmelin

Abstract

In laboratory cultures of setting oyster larvae,Crassostrea virginica, it was noted that few of many exposed cultch shells collected most of the set. Also, setting, was very sporadic with respect to time. Several hypotheses were tested to explain such observations. Individual cultch shells were not differentially attractive to setting larvae. However, cultch shells containing 24-hour-old spat or 2-month-old spat attracted more set than unspatted control shells in the same culture and stimulated more set than that received in separate control cultures. Undersides of bottom-most layers of shells attracted more set than the higher layers of shells in laboratory cultures. Two-month-old spat, inside larval-proof plankton mesh bags, stimulated set on shells outside the bags indicating that a water-borne pheromone may be the stimulating agent. These findings confirm the contention of Crisp (1967) that gregarious setting occurs inC. virginica.