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 Mnem iopsis leidyi from gut contents, digestion rates, and densities of pre dators and prey during 9 d in July 1991 at 4 stations in Chesapeake Ba y, USA, These predation rates were compared to egg and larval mortalit y rates measured concurrently in ichthyoplankton surveys. Daily predat ion by medusae and ctenophores was 19 +/- 13% (mean +/- SD) of the egg s 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, medusa e consumed 29 +/- 14% d(-1) of the larval hay anchovy, which was 41 +/ - 35% of total estimated larval mortality. Predation on larvae by cten ophores was not detected. These predation effects are compared with th ose measured concurrently in free-drifting 3.2 m(3) mesocosms. We conc lude that medusae, which had high feeding rates but low abundances, an d ctenophores, which had low feeding rates but high abundances, were i mportant predators of bay anchovy eggs and larvae in the mesohaline re gion of Chesapeake Bay.