Effect of temperature, season, and stage of life cycle on salinity tolerance of the estuarine crab Helice crassa Dana (Grapsidae)
Survival of juvenile and mature specimens of Helice crassa Dana 1851 (Brachyura: Grapsidae) collected during summer, and of mature crabs collected in winter was measured at various salinity and temperature combinations. Summer crabs were euryhaline and eurythermal, and had low mortality after 7 days in salinities of 3.5–52.5%. at temperatures of 5–30 °C. Mortality was high in all salinities at 35°C and at all temperatures in 0.35%., however, juveniles had longer times to 50% mortality than mature crabs in 0.35%. at temperatures from 10–20 °C. Mature crabs had significantly better survival (P < 0.05) in 52.5%. at 5, 10, and 30 °C than juveniles. Juveniles showed widest salinity tolerance at temperatures closest to field temperatures at time of collection; lower and higher temperatures reduced the salinity range in which maximum survival was possible. No consistent effect of temperature on salinity tolerance of mature crabs was apparent. Winter crabs had significantly higher survival (P < 0.05) in 0.35 %. at the three temperatures tested (5, 10, and 20 °C) compared with summer crabs. The salinity tolerance of stage 1 zoeae released from ovigerous female H. crassa maintained in the laboratory was investigated at 20 °C. Larvae were stenohaline, and had 100% mortality within 1 hour's exposure to salinities of 3.5–10.5 %., and within 24 h in 14%.; there was no mortality in 35%. until after 48 h. Combination of wide salinity—temperature tolerances, seasonal acclimatization giving enhanced survival in dilute salinity during winter, and the refuge of a burrow during extreme physico-chemical conditions allows the benthic stages of H. crassa to occupy the most dilute regions of an estuary. In these latter areas, concentration of the vertical distributions of ovigerous females to highest shore levels ensures that larvae are released into salinities within their limited tolerance range.