Ontogenetic changes in salinity and temperature tolerance in the doughboy scallop, Mimachlamys asperrima

Embryos and larvae of the doughboy scallop, Mimachlamys asperrima, were held at temperatures in the range from 9 to 24°C and exposed to salinities in the range from 27.5 to 40 ppt. At each stage in ontogeny, salinity optima remained Constant at 32.5 ppt; however, optimal temperatures differed and there were significant interactions between the effects of salinity and temperature. Percent development of eggs to D-veliger stage was greatest at a temperature of 17°C, whereas mean larval survival and shell length increase were greatest at 21 and 24°C, respectively. Overall, larvae were more tolerant of extremes in both salinity and temperature than embryos. Juvenile (18 mm shell height) and maturing (28 mm shell height) M. asperrima held at temperatures of 14 or 24°C and exposed to salinities in the range of 15-40 ppt grew rapidly at 24°C but exhibited salinity optima (32.5-35 ppt) similar to those at the earlier ontogenetic stages. Maturing scallops were, however, less tolerant of salinity reductions than were their smaller conspecifics. For both juvenile and maturing M. asperrima, initial behavioral responses, such as byssogenesis, provided a guide to longer term growth and survival. In general, salinity and temperature optima were seen as reflecting the environmental conditions likely to be experienced by the respective ontogenetic stages within Jervis Bay. However, response of embryos in particular to reduced temperature was inconsistent with the geographic range of M. asperrima and was thought to reflect either genetic differences in stocks or preconditioning.