Foraging Patterns of Two Syngnathid Fishes: Importance of Harpacticoid Copepods

The diets of juvenile (<g0 mm) Syngnathus scovelli and of H~ppocampus zosterae, abundant members of a resident fish community in a Thalassia testudnum seagrass bed in Tampa Bay, Florida, were examined from Apnl to October 1984. Harpacticoid copepods comprised most of the diet, both in terms of percent number and percent biomass, for the smaller size classes of S. scovelli and for H. zosterae, and harpacticoids generally had the highest index of relative importance (IRI) for both syngnathids. S. scovelli displayed ontogenetic switching to larger food items, such as amphipods. shrimp and crustacean eggs. Harpacticus sp. 1 was the most common harpacticoid copepod species found in the guts of the 2 syngnathids, but was only rarely encountered in prey samples from seagrass blades. Three other harpacticoids, Paradactylopodia brevicornis sp., Dactylopodia tisboides and Harpacticus sp. 2 had high IRIS in H. zosterae but not in S. scovelli. Vanderploeg & Scavia's selectivity index (E') was calculated for sampling dates when both species of syngnathids were most abundant, using prey density on seagrass blades as a measure of prey avadabhty. Only the harpacticoid Harpacticus sp. 1 had high positive selectivity values. MARINE ECOLOGY PROGRESS SERIES Mar. Ecol. Prog. Ser.