TROPHIC ECOLOGY OF THE DOMINANT FISHES IN ELKHORN SLOUGH, CALIFORNIA,1974-1980

Food habits of the dominant fishes collected from 1974 to 1980 at eigh t locations in Elkhorn Slough, California, and the adjacent ocean were investigated. Epifaunal crustacea was the major prey group identified from stomach contents of more than 2,000 fishes, followed by epifauna l and infaunal worms, and molluscs. Overall, 18 fish species consumed 263 different prey taxa, ranging from 10 taxa to 125 taxa per fish spe cies and including 99 crustacean, 56 polychaete, and 39 molluscan taxa . Mean prey richness was greatest at stations near the ocean and lowes t at inshore stations. Detailed dietary data for all prey taxa were su mmarized as trophic spectra for each fish species. Trophic spectra rep resented functional groups of prey and were used for comparisons of di etary similarity. Cluster analyses, based on trophic spectra, resulted in four feeding guilds of fishes. Of 18 fish species, seven (Amphisti chus argenteus, Leptocottus armatus, Embiotoca jacksoni, Clevelandia i os, Gillichthys mirabilis, Cymatogaster aggregata, and Citharichthys s tigmaeus) fed principally on epifaunal crustacea. Four species (Pleuro nectes vetulus, Platichthys stellatus, Phanerodon furcatus, and Myliob atus californica) consumed mostly molluscs and infaunal worms. Two spe cies (Psettichthys melanostictus and Triakis semifasciata) fed on mobi le crustacea, and five species (Hyperprosopon anale, Engraulis mordax, Clupea pallasi, Atherinopsis californiensis, and Atherinops affinis) fed largely on zooplankton and plant material. Our results suggest tha t high food availability enhances the nursery function of inshore habi tats, and emphasize the importance of invertebrate prey populations an d the indirect linkage of plant production to the ichthyofaunal assemb lage, particularly marine immigrant species that are likely 'estuarine dependent.'