A response-surface approach to the combined effects of temperature and salinity on the larval development of Adula californiensis (Pelecypoda: Mytilidae). II. Long-term Larval survival and growth in relation to respiration

Larvae of the bivalve molluso Adula californiensis (Phillippi, 1847) were reared for 3 days, from fertilization to veliger stage, at optimum conditions (15°C, 32.2 S), and then transferred to experimental temperatures and salinities for 22 more days to determine the effects of these factors on survival and growth. For larvae surviving to 25 days, maximum survival was estimated, by response-surface techniques, to occur at temperatures below 10°C and at salinities above 25. A comparison of 60% survival response contours for 3, 15 and 25-day old larvae indicated a progressive shift in temperature and salinity tolerance with age of larvae. The older larvae became more tolerant to reduced salinity, but less tolerant to high temperatures. Growth of the larvae over 25 days of culture was slight, and relatively independent of temperature and salinity conditions found in the environment. Oxygen consumption of 3-day old veliger larvae measured at various combinations of temperature and salinity generally increased from 7° to 18°C, and then sharply decreased from 18° to 21°C. A plateau of oxygen consumption from 9° to 15°C at 32.9 S indicated that the larvae are adapted to oceanic rather than estuarine conditions. A comparison of 25-day larval survival, mean length, and growth, with oxygen consumption of 3-day old veliger larvae indicated that high temperatures (15°C, and above) coupled with reduced salinities (26.1, and below) were unfavorable for prolonged larval life. Because of the lack of larval adaptations to estuarine conditions, larva survival and, hence, successful recruitment of this species within Yaquina Bay (Oregon, USA) depends upon the essentially oceanic conditions found only during the summer in the lower part of the Bay.