A study of some macro-faunal associates of oysters, Crassostrea virginica Gmelin in an area of low salinity and artificially elevated temperatures.

An investigation of the macro-epifaunal community on oysters suspended at intake and in the cooling lake of the Houston Lighting and Power Company Cedar Bayou power plant was conducted from February 1973 to March 1974. Temperature, salinity, dissolved oxygen, pH and chlorophyll a were measured weekly. Live oysters and oyster boxes of matched oyster shell valves were used to monitor the development of the fouling community in terms of species composition and numerical abundance. Asbestos plates were exposed for 2-week and 4-week intervals to monitor the arrival of setting organisms and to determine the periods of greatest setting abundance. The biotic accumulation were further quantified by measuring the dried and evolved weights of material in 100 cm2 areas of the fouling plates. The extreme temperatures measured during the study were 38.0 degrees C and 6.5 degrees C. Temperatures averaged about 4.0 degrees C warmer at the warmest cooling-lake station (station 1) than at the intake. The yearly mean salinity was less than 5.0 ppt as a result of rainfall which exceeded a 30-year mean by about 70%. The mean values calculated for chlorophyll a concentrations for the period between February and October 1973 were less than 10 mg/m3 at the intake and in the cooling lake. For the period between October 1973 and March 1974 mean chlorophyll a values ranged from about 15 mg/m3 to 25 mg/m3 (stations 1 and 4, respectively) at the cooling-lake stations, whereas mean values at the intake were only about 5 mg/m 3. The relatively low number (23) of species found in association with the oysters is indicative of the stressful, low salinity regime that prevailed during most of the year. Ten species were identified as potential deterrents to oyster production in the Cedar Bayou cooling lake. Callinectes and Stylochus are known predators of oysters, Polydora weakens the oyster by boring into the shell and causing mud blister formation, and Bimeria, Brachidontes, Congeria, Balanus, Corophium and Bowerbankia all contribute to the accumulation of smothering masses in oyster communities. With the exception of an unidentified flatworm, Brachidontes and a gammarid amphipod, all of the species which colonized cooling-lake substrates, were also found at the intake. Crassostrea, on the other hand, appeared in very low abundances at the intake but were absent from the cooling lake. In general species which occurred both at the intake and cooling lake were more abundant in the cooling lake on a seasonal basis. Barnacles, hydroids, ectoprocts and tube-building amphipods were seasonally abundant and contributed large masses to the communities on collecting substrates. Barnacles were the largest contributing to the dry weight of material deposited on the fouling plates, and amphipod tubes were the prime contributors to the evolved weights recorded. The period when biomass accumulations were greatest in the cooling lake was July through October 1973 when extreme values of 21.3 g/cm2 and 2.3 g/cm2 were recorded for dried and evolved weights, respectively. The only significant accumulations of material on the fouling plates suspended at the intake occurred in August 1973 when the extreme dried weight was 16.9 gm/cm2 and the greatest evolved weight was 1.4 gm/cm2.