Trophic interactions of chaetognaths, larval fish, and zooplankton in the South Atlantic Bight

Abstract

Chaetognaths are highly abundant carnivores in marine environments, and feed both on fish larvae and on the same foods as fish larvae. We assessed predation by chaetognaths on winter-spawned fish larvae and on the planktonic food of fish larvae in February 1992, December 1992, and February 1993 off the southeastern U.S. coast. Feeding rates of chaetognaths were calculated from gut content analysis and experimentally determined digestion rates, and combined with estimates of in situ densities of predators and prey. Chaetognath and larval fish distributions overlapped temporally and spatially on all dates. Densities of chaetognaths averaged 10 to 67 m-3, and fish larvae averaged 0.1 to 1.8 m-3. Only 1 fish larva was found in 6718 chaetognath guts examined. Effects of chaetognath predation on the abundant small prey consumed by the small fish larvae present in December 1992 and February 1993 were negligible (0.3 to 0.7% consumed d-1). In February 1992, however, chaetognaths consumed up to 44% d-1 of standing stocks of large copepods that also were prey of the large fish larvae present on that date. We conclude that chaetognaths were not important predators of fish larvae during this study, but may, at times, consume substantial amounts of the copepod populations, which are shared by fish larvae.