COMBINED EFFECTS OF SALINITY AND TEMPERATURE ON THE FEEDING, REPRODUCTIVE, AND SURVIVAL RATES OF EUPLEURA CAUDATA (SAY) AND UROSALPINX CINEREA (SAY) (PROSOBRANCHIA: MURICIDAE)

¹ Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut 06460

1. At all temperatures studied the limited feeding of Urosalpinx cinerea and Eupleura caudata at 12.5 indicates that this salinity is near the lower limit for feeding.

2. The feeding rates increased with each increase in temperature and salinity.

3. The maximum feeding rates were at the highest temperature-salinity combination studied (25° C, 26.5).

4. At all temperature and salinity combinations U. cinerea consumed more oyster spat than did E. caudata. Given equal populations, therefore, U. cinerea is the more important of the two species as a predator of Crassostrea virginica.

5. Both species of drills exhibited cannibalism in the presence of alternative food sources, but E. caudata did so to a greater extent than U. cinerca.

6. Cannibalism increased as the feeding rate increased, and the highest incidence of cannibalism was at optimum feeding conditions.

7. In all instances of cannibalism the predators were female drills.

8. The mortality rates of both species of drills increased with increasing temperature and decreasing salinity.

9. Mortality was highest at the highest temperature and lowest salinity combination (25° C, 12.5) and lowest at the lowest temperature and highest salinity (15° C, 26.5).

10. E. caudata was less tolerant than U. cinerea to low salinities at all temperatures.

11. E. caudata began ovipositing at 15° C and 20, and U. cinerea at 20° C and 20.

12. The number of egg capsules deposited by each species of drill increased with each increase in temperature and salinity; the maximum number was deposited at 26.5 at all temperatures studied.

13. The number of eggs in each capsule did not appear to be affected by temperature or salinity.