Relative predation potentials of scyphomedusae ctenophores and planktivorous fish on ichthyoplankfon in Chesapeake Bay

The relative predation potentials on ichthyoplankton of the scyphomedusa Chrysaora quinquecjrrha, the ctenophore Mnemiops~s leidyi and the bay anchovy Anchoa mjtchllli from Chesapeake Bay, USA, were estimated in 3.2 m3 in situ mesocosm enclosures and in 1.0 m3 laboratory tanks. For all 3 predators, averaged predation mortality (d-') and volume-specific clearance rates (1 d-' ml-') were higher and less variable when bay anchovy eggs were prey than when goby Gobiosoma bosci larvae 13.0 to ca 10.0 mm standard length (SL)] were prey. The smallest larvae (3.0 to <5.5 mm SL) were more vulnerable than eggs or larger larvae. Averaged mortality rates per scyphomedusa (0.78 and 0.32 d-' on eggs and larvae respectively) were 7 times higher than those per ctenophore (0.11 and 0.04 d-l), and almost 2 times higher than those per bay anchovy (0.37 and 0.21 d-l). However, volume-specific clearance rates by the relatively small bay anchovy predators were higher (ca 500 1 d-' ml-l) than those of the gelatinous predators. The volume-specific clearance rates of the ctenophore and medusa were only 4 and 7 % respectively of that for the anchovy. Combined species results suggest that these predators may consume 20 to 40 % daily of the fish eggs and larvae in mid-Chesapeake Bay. The scyphomedusa potentially is the most important predator on summer ichthyoplankton due to its overall abundance, high clearance rates and temporal CO-occurrence with vulnerable life stages of fish.