Salinity and thermal preference of Dungeness crabs in the lab and in the field: Effects of food availability and starvation

Abstract

Combined field and laboratory experiments were carried out to investigate the salinity and thermal preference of adult Dungeness crabs, Cancer magister (Dana). In the field, crabs were fitted with archival CTD data tags to monitor the salinity, temperature and depth experienced at 10min intervals. Crabs spent the majority of time in conditions that did not present a physiological challenge and at depths below 15m. However, all crabs that were at large for more than a week made migrations to depths shallower than 15m. Exposure to stressful salinity and temperature conditions in shallow water (<15m) showed a distinct pattern and could be divided into short exposure times (<20min) associated with movements to deeper water which were indicative of avoidance behaviour, and longer exposure periods that suggest animals were actively foraging in the shallows of the estuary. Results obtained from laboratory preference experiments using salinity (16 to 32) and temperature gradients (8 to 22°C) confirmed data from tagged crabs in the field. Overall, crabs showed a strong avoidance of low salinity. However, when crabs that had been starved for 21d were presented with a food stimulus in low salinity, they showed directed movements towards the stimulus and spent more time in low salinity. Likewise, when presented with a food stimulus in high temperatures, starved crabs spent more time searching for food in high temperature than those which had recently fed. The results of this study suggest that crabs are primarily exploiting estuarine habitats under optimal environmental conditions, but that exposure to deleterious salinities or temperatures may be altered by the presence of food.