The study of trophic interactions is fundamental to ecology, but characterizing the full trophic network of a species is often challenging. Gut content analysis has been useful in the study of fish diets, but has limitations. Assessment of trophically transmitted parasites may be a useful compliment to traditional gut content analysis, as parasites are integrated in a host over time, and the presence of larval parasites may indicate the predators of a given host.
In the kelp forests of the Santa Barbara Channel, California, USA there are several sympatric species of surfperch (Embiotocidae) that have significant diet overlap. We evaluated the use of parasites to describe the trophic network of kelp forest surfperches by asking the following questions: 1. What is the parasite assemblage of kelp forest surfperch, and 2. Do differences in parasite assemblage reflect differences in diet composition? We surveyed the metazoan parasites of the kelp perch (Brachyistius frenatus), black perch (Embiotoca jacksoni), pile perch (Rhacochilus vacca), rainbow seaperch (Hypsurus caryi), and rubberlip perch (Rhacochilus toxotes). We collected diet data from the literature, and constructed dissimilarity matrices using standardized prey importance and parasite assemblage. We then compared dissimilarities in parasite assemblages with dissimilarities in diet composition.
Larvae and adults of trophically transmitted parasites were present in all species of perch. Pile and kelp perch shared the fewest parasites with other species, while the black perch shared the most parasites with other perch species. Two parasite species (a larval tapeworm and a larval thorny-headed worm) were found in all 5 perch species, but parasite prevalence and abundance differed. Overall, parasite assemblages were more different than diet assemblage. Moreover, there were no instances where a species of perch shared all of its parasites with another perch species. This was not the case with diets, as three perch species were identical in terms of diet richness. The diverse assemblage of parasites allowed us to add information to the trophic network and separate the niche space of these fish species, even when parasite abundances were ignored.