RECRUITMENT OF BAY SCALLOPS ARGOPECTEN IRRADIANS IN FLORIDAN GULF-OF-MEXICO WATERS - SCALES OF COHERENCE

Conventional wisdom suggests that pelagically borne marine invertebrat e larvae are dispersed considerable distances from their source popula tion, but recent research provides evidence that at least in some inst ances larvae may be retained within the local environment. From June 1 995 through June 1996, we monitored adult abundance and juvenile recru itment 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 abu ndances (generally <5 scallops per 600 m(2) survey transect) during 19 95 and 1996, whereas populations at our Steinhatchee and St. Joseph Ba y 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 pe r collector per day. In contrast, recruits were common at Steinhatchee and St. Joseph Bay, where daily recruitment rates exceeded those obse rved at Anclote and Homosassa by 1.5 to 2 orders of magnitude. Whereas differences in adult abundance and juvenile recruitment were pronounc ed among sites, differences among stations within each site were minor and generally not significant. Based upon these observations and know ledge of the distribution and abundance of bay scallops in Floridan Gu lf of Mexico waters, our results suggest that during 1995-96, dispersa l of bay scallop larvae was widespread within each study site but that transport of larvae away from the adult habitat was uncommon and ulti mately unsuccessful. We discuss oceanographic features that may suppor t local retention of bay scallop larvae along the west coast of Florid a, and we suggest that periodic interruptions of those oceanographic p rocesses may explain the previously reported genetic homogeneity among bay scallop populations in Florida.