Predation by the scyphomedusan Chrysaora quinquecirrha on Mnemiopsis leidyi ctenophores

Numerous species of gelatinous zooplankton are known to eat ctenophores, but their predation interactions have seldom been studied. Laboratory experiments showed that Chrysaora quinquecirrha medusae ( 3 to 20 mm diameter) usually consumed entire ctenophores (Mnerniopsis leidyi) that were equal in diameter or smaller. Although ctenophores larger in diameter than medusae were sometimes consumed completely, often only the lobes of the ctenophores were eaten. These damaged ctenophores healed in the laboratory. Short-lobed ctenophores had reduced fecundity, and probably lowered feeding rates as well. Short-lobed ctenophores were abundant (24 to 76% of the population) in situ during 1990. Large medusae (40 to 120 mm diameter) in 3.2 m3 in situ mesocosms cleared ctenophores at high rates (up to 6180 1 d-'). Clearance rates of medusae decreased with increasing ctenophore density and s u e , and increased with medusa size. The laboratory-determined clearance rate equation, in combination with medusa sizes and densities in situ, predicted that medusae could eliminate ctenophores from a tributary, but not at 2 stations in the main-stem Chesapeake Bay (USA), which was in agreement with in situ population data. The multlple negative effects of C. quinquecirrha on M. leidyi populations may lead to complex community-level changes that actually may reduce mortality of zooplankton and ichthyoplankton.