RELATIVE PREDATION POTENTIALS OF SCYPHOMEDUSAE, CTENOPHORES AND PLANKTIVOROUS FISH ON ICHTHYOPLANKTON IN CHESAPEAKE BAY

The relative predation potentials on ichthyoplankton of the scyphomedu sa Chrysaora quinquecirrha, the ctenophore Mnemiopsis leidyi and the b ay anchovy Anchoa mitchilli from Chesapeake Bay, USA, were estimated i n 3.2 m3 in situ mesocosm enclosures and in 1.0 m3 laboratory tanks. F or all 3 predators, averaged predation mortality (d-1) and volume-spec ific clearance rates (l d-1 ml-1) were higher and less variable when b ay anchovy eggs were prey than when goby Gobiosoma bosci larvae [3.0 t o 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. Avera ged mortality rates per scyphomedusa (0.78 and 0.32 d-1 on eggs and la rvae respectively) were 7 times higher than those per ctenophore (0.11 and 0.04 d-1), and almost 2 times higher than those per bay anchovy ( 0.37 and 0.21 d-1). However, volume-specific clearance rates by the re latively small bay anchovy predators were higher (ca 500 l d-1 ml-1) t han those of the gelatinous predators. The volume-specific clearance r ates of the ctenophore and medusa were only 4 and 7 % respectively of that for the anchovy. Combined species results suggest that these pred ators may consume 20 to 40 % daily of the fish eggs and larvae in mid- Chesapeake Bay. The scyphomedusa potentially is the most important pre dator on summer ichthyoplankton due to its overall abundance, high cle arance rates and temporal co-occurrence with vulnerable life stages of fish.