CURTIS, DL; MCGAW, IJ; University of Nevada, Las Vegas; University of Nevada, Las Vegas: Feeding and digestion in low salinity: behavioural adaptations to avoid physiological multitasking in the Dungeness crab Cancer magister

The salinity regimes of estuaries change on a regular basis, imparting varying levels of physiological cost on their inhabitants. The costs associated with osmoregulation may be compounded by an increase in metabolic parameters associated with feeding and digestion. The Dungeness crab, (Cancer magister), inhabits sandy bays and estuaries and is classified as a weak osmoregulator. Although this species can survive in salinities as low as 11ppt, it exhibits behavioural responses to low salinity that may reduce the use of physiologically costly mechanisms. In the laboratory, there was a decrease in feeding rate as well as the percentage of animals feeding as a function of salinity. Crabs ceased feeding in salinities below 16ppt (50% seawater). Despite the added metabolic demands of digestive processes, pre and postprandial C.magister exposed to both a high (20-28ppt) and low (10-24ppt) salinity gradient showed no difference in salinity preference. Crabs were able to detect differences in salinity as low as 2ppt, showing preference for the highest salinity offered. In the Sarita estuary, British Columbia, crabs fitted with CTD data tags were exposed to salinities from 18-32ppt. Exposure periods to low salinity lasted from less than 10min up to 10h. This work serves as important baseline data for planned studies on feeding and digestion in physiologically challenging environments.