Impacts of salinity fluctuations on the productivity of coastal mangrove fish populations

An empirical study examined the influence of salinity fluctuations on the key population demographic characteristics (i.e., survivorship, growth, and reproduction) of two types of mangrove fish populations (i.e., Poeciliidae and Cyprinodontidae). Livebearers (Family Poeciliidae) exhibited significant mortality following large, instantaneous salinity increases, while large instantaneous salinity decreases had no significant effect on mortality rate. Instantaneous salinity changes had no significant effect on killifish (Family Cyprinodontidae) mortality rates. Poecilia latipinna and Cyprinodon variegatus were reared and grown at four static levels of salinity and one dynamic salinity treatment. Growth rate varied significantly among salinity treatments and tended to be highest in the 26 ppt treatment and least in the 43 ppt treatment. Condition factor tended to be somewhat lower in the 43 ppt treatment. Gonadosomatic index (GSI) values were highest in the high salinity treatments. Poecilia latipinna fecundity was significantly higher in the hyper-saline treatment relative to the dynamic treatment. However, C. variegatus fecundity tended to decrease with increasing salinity level, though not significantly. Female age and size at maturity tended to decrease with increasing salinity and occurred earliest and at the smallest size in the 26 ppt treatment. Male C. variegatus age at maturity varied significantly with salinity, it occurred latest at 11 ppt. Salinity specific effects on growth and reproductive parameters, derived from the analytical experiments, were then incorporated into the basic components of the existing Across Trophic Levels System Simulator everglades restoration model for fish functional groups in freshwater marshes. Model simulations showed that salinity can affect population productivity in these species. Simulated population productivity tended to be higher at 26 ppt when compared to simulated productivity at 43 ppt.