Enhanced Blue Crab Predation on Rangia Clams after Exposure to Hypoxia

Hypoxia or dissolved oxygen concentrations < 2 mg/L is a problem in estuaries worldwide. In Lake Pontchartrain, a 250 km de-faunated zone exists as a result of salinity stratification and episodic hypoxia. Mature common rangia clams (Rangia cuneata) are not found within this zone. Blue crabs (Callinectes sapidus) are important estuarine predators and may move in and out of the hypoxic zone to feed on hypoxia-stressed rangia clams. To test the effects of hypoxia on predation, rangia clams were exposed experimentally to severe hypoxic conditions (< 0.75 mg/l) for 72-hours and then presented to blue crabs. One hypoxic and one normoxic clam were added to each aquarium containing a blue crab for each trial, and crab feeding choices were observed and recorded. I found prey choice varied among crabs, but in general, the experimental data demonstrates that crabs chose to feed on hypoxia-stressed clams over clams kept under normoxic conditions.