Contributions of heterotrophic and autotrophic prey to the diet of euphausiid, Euphausia pacifica in the coastal waters off northeastern Japan

摘要

The contributions of heterotrophic and autotrophic prey to the diet of Euphausia pacifica were examined in coastal waters off northeastern Japan in May and October 1999. The autotrophic contribution was estimated from gut pigment contents, and the heterotrophic contribution from the volume of each taxonomic group in the stomach. Our observations suggest that heterotrophic prey, especially copepods, were more important than autotrophic prey in both seasons. The contributions of heterotrophic prey items in adult E. pacifica ranged from 57-79% in May and from 27-93% of the total ingested carbon in October. The contribution of copepods was largest, ranging from 54-77% in May and from 27-93% in October. We discuss the contribution of athecate ciliates, another possible heterotrophic prey of importance, to the diet of E. pacifica.