Freshwater ecology

The viability of the eastern oyster, Crassostrea virginica, is designated as an ecological performance measure for the management of freshwater inflows to the St. Lucie Estuary, Florida. Thus, oysters derived from the St. Lucie Estuary were tested for their physiological response to stress, measured as altered condition index and RNA/DNA ratios, resulting from changes in salinity and infection by the protozoan parasite Perkinsus marinus, the agent of Dermo, a common oyster disease. Pilot studies consisted of the development of a real-time PCR-based assay for P. marinus infection, procedures to infect oysters with the pathogen by injection method and procedures for the measurement of RNA/DNA ratios. The general experimental design was to assess the response of non-injected and injected C. virginica to low salinity challenges. Two scenarios for salinity stress were tested: one in which oysters were subjected to a single reduction in salinity and one in which an initial reduction in salinity was followed by a recovery phase and then subjected to a second challenge of reduced salinity. Condition index was more responsive to changes in salinity regimes than to P. marinus infection. Changes in the RNA/DNA ratio were responsive to the infection status, but not changes in salinity; the pattern of change in the RNA/DNA ratio generally followed changes in the measured levels of infection. The lack of mortalities showed that these oysters were able to tolerate short periods of reduced salinity.

The largemouth bass (Micropterus salmoides) fishery was at an all time low on Lake Okeechobee when experimental supplemental stockings were done to try and enhance local bass populations. Largemouth bass had never been stocked on a large lake like Lake Okeechobee. The objectives were to develop a methodology, study dispersal, and compare stocked versus wild bass habitat choices. The methodology underwent considerable changes between studies. Bass dispersed to the edges by the second sampling period, so a larger sampling area may be needed. Water depth and pH were found to be significantly different between wild and stocked bass. Hatchery bass are naèive about predators, which may have resulted in stocked bass not moving to shallower areas like wild bass. The pH was weakly correlated with depth, so differences may be partially due to the fact that as depth increases, pH may also increase.