MCGAW, IJ; University of Nevada, Las Vegas: Prioritization or summation of events? Physiological responses of postprandial Dungeness crabs in low salinity

The Dungeness crab, Cancer magister, inhabits sandy bays and estuaries and is classed as a weak osmoregulator. During exposure to low salinity the crabs reacted with an increase in heart rate, but a large decrease in cardiac stroke volume resulted in a decrease in cardiac output. Hemolymph was diverted from the legs and digestive structures and shunted to abdominal regions and the supraesophageal ganglion. Changes in cardiac parameters were accompanied by an increase in ventilation rate. In contrast, following feeding in 100% seawater, there was an increase in cardiac output, driven by an increase in both stroke volume and heart rate. Hemolymph flow rates to the mouthparts increased during feeding; perfusion of the foregut and hepatopancreas increased during digestion. Ventilation of the branchial chambers also increased. The question then arises if responses to low salinity or digestion are prioritized, or if summation of these opposing factors occurs. Dungeness crabs were exposed to 50%SW and 25%SW during or following feeding episodes. There were slight increases in cardiac parameters and hemolymph flow rates following feeding in 50%SW, but these were not as pronounced as those occurring in normal seawater. In 25%SW cardiac and ventilatory events in response to low salinity were prioritized. This suggests that salinity has a dominant effect on physiological parameters, thus slowing or halting digestion. These findings are backed up by our work on behavioral responses and feeding behavior of Dungeness crabs in low salinity.