EFFECTS OF SALINITY AND TEMPERATURE ON THE PREDATION RATE OFTHAIS HAEMASTOMAONCRASSOSTREA VIRGINICASPAT

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Abstract
Predation rates of T. haemastoma on C. virginica spat were determined in constant salinities of 7.5, 10, 15, 20, 25, 30 and 35.permill. S[salinity] and at 10, 20 and 30.degree. C. Drills also were exposed to 2 diurnal tidal fluctuation cycles of 10-30-10.permill. S and 30-10-30.permill. S at the 3 temperatures. Predation rates were determined as the number of spat consumed daily and the total dry weight of oyster flesh consumed over 21 days. No predation occured at 10.degree. C. Predation increased successively at 20 and 30.degree. C where different patterns of predation occurred. There was a broad optimal plateau for predation between 10 and 30.permill. S at 20.degree. C, but at 30.degree. C predation rates declined at salinities above 30.permill. S. Statistical analysis (2-way Anova [analysis of variance]) of the data for the 20 and 30.degree. C treatments indicated that temperature and salinity and their interaction were significant (P < 0.05) factors affecting predation. The sex, weight and length of the drills did not significantly affect predation rates. Predation rates in the 2 fluctuating salinity cycles were not significantly different at 20 or 30.degree. C. The overall effect of tidal fluctuations of salinity was to reduce predation rates. An additional experiment was performed to determine the temperature threshold for predation. Predation rates were determined at 12.5, 15.0 and 17.5.degree. C and 20.permill. S. Predation rates increased linearly with temperature at this salinity.