Laboratory studies of predation by the ctenophore Mnemiopsis leidyi on the early stages in the life history of the bay anchovy, Anchoa mitchilli

Abstract

The lobate ctenophore, Mnemiopsis leidyi, consumed eggs and larvae of the bay anchovy, Anchoa mitchilli, in laboratory experiments. This ctenophore exhibited a type I functional response to increases in egg densities without reaching saturation at high prey densities. Clearance rate increased with increasing experimental container volume. There was a 3-fold increase in the volume of water cleared by 2.0–2.5-cm ctenophores and a >5-fold increase for 4.5–5.0-cm ctenophores in 15–1 versus 100–200–1 containers. Clearance rate was dependent on tenophore length but was probably underestimated for the larger animals due to container effects. The presence of various densities of alternate prey, Acartia hudsonica or Anemia sp. nauplii, in addition to Anchoa mitchilli eggs did not affect the clearance rates on the eggs alone. Comparison of clearance rates of 2.0–2.5-cm ctenophores on various ages of starved and fed bay anchovy larvae indicated that predation may be higher on yolk-sac larvae than on eggs but decreases as the larvae grow. After 3 days post hatch starved anchovy larvae become more vulnerable to predation than fed larvae. The ctenophore, M.leidyi has the potential to inflict substantial predation pressure on early stages in the life history of bay anchovy.