Environmental and Biogeographic Factors Influencing Ichthyofaunal Diversity: Indian River Lagoon

The geomorphology, transitional climate, geographic and shallow marine setting of the Florida peninsula extending 1,120 km from 24.6° to 30.8°N latitude has allowed great aquatic biological diversity to develop along its east coast. A compressed gradient in mean hydrologic and climatic environments and high habitat diversity along the coast and within the Indian River Lagoon creates conditions that allow the co-existence of widely diverging faunas adapted to both temperate and tropical biogeographic regions of the western Atlantic, Caribbean and Gulf of Mexico. Warm tropical currents flowing from the Caribbean Sea bathe the peninsula throughout the year and carry larvae and juveniles of many tropical euryhaline and marine species to the Indian River Lagoon. A variety of optimal physical conditions allows settlement and survival of these fishes, producing one of the richest biotas in North America. At present 782 species in 140 families have been recorded from the region, 397 from the Indian River Lagoon system. Long term quantitative studies of particular fish communities within the Indian River Lagoon reveal high species richness in specific habitats. Estuarine-ocean inlet seagrass meadow fish faunas are ontogenetically coupled with rich nearby ocean reef fish communities and support the richest estuarine ichthyofauna (214 species from seagrasses, 282 from ocean inlets). A biogeographic analysis reveals that freshwater, seagrass and mangrove fish communities have a heterogeneous mix of species with at least 10 different faunal distributional tracks represented. Of the top 25 species in percent frequency of occurrence, 52% in seagrass and 60% in mangroves, are tropical. Freshwater habitats support 118 species with faunal assemblages unique to this region of the United States. These rich fish faunas are impacted by anthropogenic activities, particularly direct or indirect habitat displacement and destruction. The Florida human population has consistently allowed the highest coastal terrestrial and aquatic native habitat destruction rate within the continental United States through coastal urbanization and uncontrolled resource utilization. With present trends in coastal human population growth there is little hope for conservation of the region's fish diversity at historical levels as the Indian River Lagoon naturally contained less wetland and submerged habitat per linear shoreline mile than any major estuary within the state of Florida.