No abstract

The effects of reestablishing a marsh-lagoon connection through culverts upon the fish populations and the physical conditions of two impounded sub-tropical marshes are examined. After install ation of the culverts, mean salinities in the two marshes increased from approximately 13 ppt to 25 ppt and pH from 7.1 to 7.3. The abundance of marsh resident species, particularly those that forage in the upper marsh, decreased significantly after connection, but utilization of the marshes by transient species increased by almost two orders of magnitude. Modification of the marsh hydroperiod seems to be most important in influencing the changes in the patterns offish utilization, abundance, and diversity observed at the study sites.

We analyzed total mercury concentration in muscle tissue of 15 serranid species (n = 1,401 fish) collected from the Gulf of Mexico and also developed a comprehensive model relating two commonly used mercury analysis methods. There was considerable interspecific and intraspecific variability in mercury within groupers and sea basses. Mean mercury concentration for individual species ranged from 0.03 to 0.91 mg/kg wet weight across all size ranges, and for legally harvestable grouper and sea bass concentrations were 0.32 mg/kg and 0.09 mg/kg, respectively. Mercury in individual fish ranged from 0.01 to 3.3 mg/kg. Approximately 23% of all grouper samples analyzed contained mercury at concentrations that exceeded the U.S. Environmental Protection Agency's methylmercury consumption guidance criterion for humans (0.3 mg/kg). Mercury in legally harvestable individuals of some species exceeded 0.5 mg/kg, and harvestable black grouper Mycteroperca bonaci had a mean mercury concentration greater than 1.0 mg/kg. A positive relationship was observed between total mercury content and both fish length and fish age. For species that feed principally on fishes (e.g., gag M. microlepis and scamp M. phenax), mean mercury concentration was greater than that for species that feed mainly on invertebrates (e.g., red grouper Epinephelus morio and sand perch Diplectrum formosum). Although overall mean mercury concentrations were relatively low, for six species the maximum mercury concentration was at a level that has been associated with sublethal effects on fish physiology and with human health risks. Current grouper management regulations in the Gulf of Mexico select for a fishery of the largest and oldest individuals, which have the greatest mercury burdens. The species‐ and size‐specific mercury data from this study can be used to inform at‐risk human populations, refine regional fish consumption advisories, and further our understanding of mercury bioaccumulation in these important fishery species.

Yearly above-ground production estimates in natural, ditched, and impounded high salt marshes along the Indian River Lagoon in east central Florida ranged from 834.9 g/m 2 in the impounded marsh to 2,316.5 g/m z in the natural one. Mosquito control activities in the impounded marsh prior to the start of this study resulted in larger stocks of dead and litter blomass there during the first year than at the other two marshes. High soil temperature and salinity during the summer may have caused a decrease in production during that season. Annual turnover rales varied from 5.8 at the impounded marsh during the first year to 1.1 at the impounded marsh and at a nearby dhched marsh during the second year. Production was inversely correlated with flooding frequency. No ~ignificant differences were found in 1he rates of litter loss from any of the sites, but lit:er from the impounded marsh had greater organic content than litter from the open and the ditched marshes. The data suggest that flooding for mosquito control during the summer can curtail production, but the effects upon yearly production are minor, as production during the summer is naturally low.