Salinity Detection and Associated Behavior in the Dungeness Crab, Cancer magister

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Abstract
Dungeness crabs, Cancer magister, showed the same antennular flicking response to brief (<2 min) salinity fluctuations as they have previously shown in detecting chemical food cues during other studies. The threshold concentrations at which 50% of the crabs detected the salinity changes were 29.9‰ and 32.7‰ or 96% and 105% of ambient seawater (31.0‰). At the maximum salinity changes used, other behaviors accompanied the flicking response. In a second experiment where salinity rose or fell continuously, two previously undescribed behaviors, pulsing and closure, occurred. In pulsing, crabs showed a rapid coordinated opening and closing of the outer maxillipeds with rapid beating of the maxillipedal flagellae. In closure, crabs stopped all overt activity, retracted their appendages and tightly closed the buccal cavity with the outer maxillipeds. Under increasing salinity crabs exhibited pulsing at 34.9‰ or 113% of ambient seawater and closure at 36.2‰ or 117% of ambient. Under decreasing salinity crabs showed pulsing at 23.2‰ or 75% of ambient seawater and closure at 15.5‰ or 50% of ambient.