PREDATION MORTALITY OF BAY ANCHOVY ANCHOA-MITCHILLI EGGS AND LARVAE DUE TO SCYPHOMEDUSAE AND CTENOPHORES IN CHESAPEAKE BAY

We measured predation on bay anchovy Anchoa mitchilli eggs and larvae by abundant scyphomedusae Chrysaora quinquecirrha and ctenophores Mnemiopsis leidyi from gut contents, digestion rates, and densities of predators and prey during 9 d in July 1991 at 4 stations in Chesapeake Bay, USA, These predation rates were compared to egg and larval mortality rates measured concurrently in ichthyoplankton surveys. Daily predation by medusae and ctenophores was 19 +/- 13% (mean +/- SD) of the eggs over the 20 h stage duration, with medusae responsible for 26 to 100% of the predation. These gelatinous predators accounted for 21 +/- 17% of the total estimated daily egg-stage mortality. On average, medusae consumed 29 +/- 14% d(-1) of the larval hay anchovy, which was 41 +/- 35% of total estimated larval mortality. Predation on larvae by ctenophores was not detected. These predation effects are compared with those measured concurrently in free-drifting 3.2 m(3) mesocosms. We conclude that medusae, which had high feeding rates but low abundances, and ctenophores, which had low feeding rates but high abundances, were important predators of bay anchovy eggs and larvae in the mesohaline region of Chesapeake Bay.