Exposure of rangia clams to hypoxia enhances blue crab predation

Abstract

This experimental study questions whether exposure of non-mobile prey to episodic hypoxia might enhance predation by a mobile predator, which moves into the former hypoxic area immediately after a shift back to normoxic conditions. We used Rangia cuneata (common rangia clam) and Callinectes sapidus (blue crab) from an oligohaline estuary where mature clams are rare in areas subject to episodic anoxia and hypoxia. Clams were exposed to severe laboratory hypoxia for 72h. One clam stressed by hypoxia and another clam maintained under aeration (normoxia) were placed in aerated aquaria containing a crab. Feeding choice of hypoxic vs. normoxic clams was then monitored for 12h. We used 20 different crabs for two experimental replicates each for a total of 40 replicates. To test for homogeneity of the feeding response, we used a 1-tail binomial test with 0.5 expected probabilities. Eleven of the 20 crabs fed (55%), and 16 out of 18 hypoxia-stressed clams were eaten first compared to two out of 18 clams kept under normoxic conditions (p=0.001). The significant frequency choice of stressed clams indicates that in this experimental study, exposure of clams to hypoxia enhanced crab predation.