INDIVIDUAL AND COMBINED EFFECTS OF SALINITY AND TEMPERATURE ON EMBRYOS AND LARVAE OF THE COOT CLAM, MULINIA LATERALIS (SAY)

1. Embryos of M. lateralis held at 25 ± 1° C developed satisfactorily (70% or more of maximum) within the salinity range from 22.5 to 30‰; 27.57‰ was optimum. Some embryos developed normally, however, at salinities as low as 15‰ (10%) and as high as 37.5‰ (1.2%). 2. Some larvae survived at all salinities tested (7.5 to 37.5‰); survival was 70% or more only within the range from 20 to 27.5‰. 3. Larvae grew satisfactorily within the salinity range from 20 to 30 or 32.5‰; 25‰ was optimum. 4. Embryos held at 27 ± 0.5‰ salinity developed satisfactorily within the temperature range from 15 to 25° C; 20° C was optimum. Some embryos developed normally, however, at temperatures as low as 10 (17.3%) and as high as 30° C (39%). 5. Some larvae survived at temperatures from 7.5 (lowest tested) to 32.5° C; survival was satisfactory from 7.5 to 27.5° C. 6. Larvae grew satisfactorily at temperatures from 20 to 30° C; 27.5° C was optimum. 7. The effects of salinity and temperature were significantly related only when the tolerance of either one or the other was approached. When the salinity was unfavorable, the range of temperature was markedly narrowed and, conversely, when both salinity and temperature were within the satisfactory range there was no significant interrelationship. 8. The range of temperature tolerance for embryos narrowed above and below 30‰ salinity, and salinity tolerance narrowed above and below 22.5° C. 9. Survival of larvae was relative uniform at temperatures of 7.5 to 27.5° C and at salinities from 10 to 35‰, but at 32.5° C (at all salinities other than 30‰) the percentage of larvae surviving was drastically reduced. 10. Growth of larvae was most rapid within the salinity range from 20 to 35‰ and within the temperature range from 22.5 to 27.5° C.