Effects of hypoxia on predator-prey dynamics of the blue crab Callinectes sapidus and the Baltic clam Macoma balthica in Chesapeake Bay

In general, hypoxia ( 8 mg O2 l -1 ) or low dissolved oxygen (low DO; < 2 mg O2 l -1 ) either without or with a male blue crab that was allowed 2 d to feed upon the clams. Predation-induced proportional mortality of clams was significantly lower under low DO than under normoxia in all 3 years. Thus, under short-term hypoxia, both crab feeding efficiency and trophic transfer from M. balthica to blue crabs were reduced. Changes in clam burial depth due to oxygen levels was determined by establishing normoxic and low DO treatments in replicate 208 l aquaria in 2 years. Burial depth after exposure to oxygen treatments for 48 h did not differ as a function of oxygen level. None of the clams died after 2 d of low DO, 27% died after ~6 d, and 90% died after 21 d. Short-lived hypoxia therefore reduces the ability of crabs to forage upon clams efficiently and increases clam survival, whereas long-term hypoxia may increase the availability of clam prey to predators through mortality and movement to the surface. Thus, short- lived hypoxia is likely to reduce the transfer of benthic prey to higher trophic levels, although longer- term exposure may increase transfer.