Recruitment of bay scallops Argopecten irradians in Floridan Gulf of Mexico waters: scales of coherence

Conventional wisdom suggests that pelagically borne marine invertebrate larvae are dispersed considerable distances from their source population, but recent research provides evidence that at least in some instances larvae may be retained within the local environment. From June 1995 through June 1996, we monitored adult abundance and juvenile recruitment in 4 geographically separated bay scallop Argopecten irradians populations occurring along the Gulf of Mexico coast of Florida, USA. Populations at our Anclote and Homosassa study sites had low adult abundances (generally <5 scallops per 600 m(2) survey transect) during 1995 and 1996, whereas populations at our Steinhatchee and St. Joseph Bay study sites had considerably higher adult abundances (generally >25 scallops per 600 m(2) survey transect) during those years. Similarly, recruitment to artificial spat collectors was a rare event at Anclote and Homosassa, where we typically collected fewer than 0.1 scallops per collector per day. In contrast, recruits were common at Steinhatchee and St. Joseph Bay, where daily recruitment rates exceeded those observed at Anclote and Homosassa by 1.5 to 2 orders of magnitude. Whereas differences in adult abundance and juvenile recruitment were pronounced among sites, differences among stations within each site were minor and generally not significant. Based upon these observations and knowledge of the distribution and abundance of bay scallops in Floridan Gulf of Mexico waters, our results suggest that during 1995-96, dispersal of bay scallop larvae was widespread within each study site but that transport of larvae away from the adult habitat was uncommon and ultimately unsuccessful. We discuss oceanographic features that may support local retention of bay scallop larvae along the west coast of Florida, and we suggest that periodic interruptions of those oceanographic processes may explain the previously reported genetic homogeneity among bay scallop populations in Florida.