Salinity-temperature and nutritional effects on the setting rate of larvae of the tropical oyster, Crassostrea iredalei (Faustino)

The combined effects of salinity-temperature and feeding (algal species and density) on the setting rate of Crassostrea iredalei larvae were studied. Six salinities (5, 10, 15, 20, 25 and 30 parts per thousand) were tested at five temperatures (24, 27, 30, 33 and 36 degrees C). A separate experiment using various algal densities (0, 25, 50, 75, 100 and 125 X 10(3) cells ml(-1))of Isochrysis galbana, Chaetoceros calcitrans and mixtures of both was conducted. The optimum salinity-temperature conditions were 20 parts per thousand and 30 degrees C, which supported the highest mean percentage (+/- S.D.) larval settlement rate of 31.4 +/- 3.4%. The use of different species of microalgae had a significant effect (P < 0.05) on the rate of larval settlement. The highest settlement rate was recorded for mixed algae (11.3%), but this was not significantly different from I. galbana (10.0%) (P > 0.05), irrespective of density. Ch. calcitrans produced 9.5% larval settlement rate, which also was not significantly different from I. galbana (P > 0.05). The effect of algae densities, irrespective of species, was that the highest set of 24.5% occurred at 100 X 10(3) cells ml(-1). (C) 2000 Elsevier Science B.V. All rights reserved.