Patterns of Abundance, Distribution, and Size Composition of the Rainwater Killifish (Lucania parva) in a Subtropical Bay
A throw-trap survey of the nearshore flora and fauna of Biscayne Bay, Florida, USA, was conducted in the shallow open-water area along the western shoreline of South Biscayne Bay (Matheson Hammock to Turkey Point) in 2005, in order to gain an understanding of fish and invertebrate species structure and assemblages of this habitat. The rainwater killifish (Lucania parva), was the most abundant species in our samples and was examined in relation to biotic and abiotic factors that might influence the distribution of this species. Individual fish were counted, weighed, and measured, while salinity, temperature, and depth were recorded at the site, and the benthic habitat was quantified on site using the Braun-Blanquet method. This survey yielded 1,990 individuals over the course of two sampling seasons that were designated as wet (August) and dry (February) seasons. Forty-seven sites were sampled each season. A length-weight relationship was generated, and density, biomass, and other abundance indices were generated. The density of L. parva at our sites was much higher than other reported densities for this species, and there was a clear seasonal trend in the abundance of rainwater killifish, with twice as many individuals in the wet season. The proportion of juveniles in the samples suggested that reproduction occurred at least twice a year, prior to both sampling periods. Salinity and density of L. parva varied inversely. Using a model developed by Diego Lirman (2007), segments of the mainland shoreline were identified as clusters having similar salinity regimes. Density and size composition varied significantly between salinity clusters. More juveniles were observed in the wet season and in cluster 2, defined by its moderate salinity and relatively low salinity variability. Significantly fewer killifish were observed within cluster 3, a cluster characterized by a high amount of canal discharge and salinity variability. Canopy height of the seagrass was the most significant factor affecting the abundance of L. parva. Coverage of Thalassia testudinum and mixed algae also appeared to play a role in the abundance of this species. Together, canopy height and salinity formed the strongest relationship with L. parva abundance. Results suggest that salinity and certain habitat variables may be accurate predictors of the abundance and distribution of this species along the mainland shoreline of Biscayne Bay. There are a number or regulations already in place that protect the mangrove habitat in which L. parva resides. Fewer regulations address critical seagrass habitats. The Comprehensive Everglades Restoration Plan aims to correct decades of destructive modifications to the hydrology of South Florida by creating a more natural sheetflow and minimizing point source freshwater discharge into Biscayne Bay. These alterations are likely to have consequences for the flora and fauna of the Bay, but will ultimately have a positive impact on many species that reside in Biscayne Bay, including the rainwater killifish.