RIVULUS-MARMORATUS - ECOLOGY OF DISTRIBUTIONAL PATTERNS IN FLORIDA AND THE CENTRAL INDIAN-RIVER LAGOON

The Neotropical killifish Rivulus marmoratus is widely distributed, bu t locally rare, throughout much of coastal south and central Florida. Habitat alteration has affected the species throughout the state, espe cially on the east coast (Indian River Lagoon) where the destruction o f mangroves and impounding of high marsh for mosquito control has alte red and fragmented suitable habitat. Within tropical salt-marsh and ma ngrove forests, R. marmaoratus seems best adapted to certain micro-hab itats, specifically those precluding the survival/establishment of com peting fishes. On the east coast of Florida, this microhabitat prefere nce is the land crab (Cardisoma guanhumi) burrow. In south Florida and the west coast, R. marmoratus is most often captured in stagnant pool s and old mosquito ditches in mangrove forests. Populations of R. marm oratus in Florida consist of arrays of homozygous clones. Can habitat fragmentation, with its possible effects on clonal diversity, affect t he continued success of this species? Are certain clones better-adapte d to specific environmental conditions? Isolated populations consistin g of only a single clone could persist indefinitely. Association with habitat type may answer some of these questions. Some degree of plasti city is apparent, as northern clones ''transplanted'' from crab burrow s survive well and achieve high population levels in isolated pools mo re typical of south Florida habitats. However, the appearance of male fish in these pools, a phenomenon unknown in natural populations from burrows, suggests aberrant population structure. While general questio ns remain about the adaptive significance of clonal diversity, the mer e presence of this novel fish in salt marsh/mangrove habitats may indi cate that other aspects of biodiversity are in good ''order.''