Mangrove shoreline fishes of Biscayne Bay, Florida

Abstract

Biscayne Bay is a shallow subtropical lagoon on Florida's southeastern coast that is bordered to the west by the mainland and to the east by barrier islands and keys. Fish assemblages inhabiting two types of mangrove-lined shoreline that encompass the Bay were examined using a visual 'belt-transect' census method over four consecutive seasons. Several significant differences were evident between shoreline habitats in terms of fish species composition, taxonomic richness and taxon-specific densities; seasonal changes and fish size-structure differences were few. The mangrove shorelines along the mainland (ML) consistently harbored less fish taxa than those on the leeward side of the islands and keys (LK), but harbored higher densities of several euryhaline forms (i.e., killifishes and livebearers). Densities of fishes that are typically associated with coral reef habitats (i.e., snappers and grunts) tended to be higher within LK vs ML mangrove shorelines, but there were exceptions (e.g., great barracuda, Sphyraena barracuda). For five fish species, length-frequency distributions were compared between the Bay's mangrove shorelines and nearby coral reef habitats. These data comparisons lent partial support to an ontogenetic 'mangrove-to-reef' migration model for only two of the five species examined. Results suggest that these shoreline habitats play varying ontogenetic and trophic roles, depending on location, season and fish species Biscayne Bay's mangrove shoreline fish assemblages appear to reflect: (1) proximity of the mangroves that they occupy to offshore reef habitats; (2) salinity regime along the shoreline; and (3) water depths within the mangrove forest interior. The fish assemblage information collected here may serve as a 'baseline' in future assessments of fishing impacts or the effects of other anthropogenic changes to Biscayne Bay and its watershed.