MOLLUSCAN BIODIVERSITY IN THE INDIAN-RIVER LAGOON, FLORIDA

Using available collection and literature resources, the mollusks of t he Indian River lagoonal system, central eastern Florida, were invento ried based largely on material collected during 1974-1982. 4,503 recor ds from 1,150 stations documented 428 species-level taxa, including 24 3 resident species. The lagoon showed a substantially higher number of species than other well-studied western Atlantic estuaries, and showe d strongest qualitative similarity to Tampa Bay, Florida. Intraregiona l analysis defined five faunal areas with unique molluscan components; 39 species were common throughout the lagoon. Inlet localities includ ed 106 species not found elsewhere, including four of the five endemic species. Seagrass beds supported the highest number of species (177), and Bittiolum varium (Pfeiffer, 1840) (Gastropoda: Cerithiidae) was m ost frequently collected as well as quantitatively most abundant. Habi tat, diet, life mode, and life history strategies were highly diverse. Analysis of species distributions supported the presence of a zoogeog raphic transition zone and established 14 new distributional records. The importance of endemic (''yoyo'' clams, one opisthobranch), commerc ial (Mercenaria spp.), and internationally protected species (Strombus gigas Linne, 1758) to management considerations is discussed.