How littoral macrophyte growth form influences foraging ecology of pumpkinseed sunfish

Freshwater littoral systems are often structured by macrophytes exhibiting a variety of growth forms. This vegetation supports invertebrate communities that are an important food resource for littoral fishes. In this study, I hypothesized that macrophyte growth form complexity affects fish foraging success through alterations in prey accessibility, behavior and abundance. Questions concerning the influence of plant growth form on several aspects of pumpkinseed sunfish (Lepomis gibbosus) foraging success were explored in the laboratory and the field with the macrophytes Scirpus validus (simple growth form) and Potamogeton amplifolius (complex growth form).; In the laboratory pumpkinseeds foraged on the microcrustacean Sida crystallina and on larval damselflies at lower rates in Potamogeton than in Scripus habitats. Predator-escape behavior in larval damselflies was expressed more frequently in Scirpus, where it reduced damselfly predation risk. In Post Pond, New Hampshire, the Potamogeton study site had a higher abundance of plant-associated prey and of pumpkinseed predators than the Scirpus site. Despite this difference, the plant-associated prey biomass ingested by pumpkinseeds did not differ in the two sites, but Potamogeton fish ingested more benthic prey. Whether pumpkinseed feeding on vegetation-prey in the Potamogeton site was limited by the complex plant growth form (as seen in the lab), or by gut filling from large benthic prey, could not be determined. Fish in Scirpus showed a preference for vegetation-prey (as a group) over benthic prey, while fish in Potamogeton showed no preference, suggesting a reduced tendency for pumpkinseeds to feed on prey associated with a complex plant growth form. In fish exclosures, plant-associated prey increased more in Potamogeton than Scirpus, indicating higher overall predation by the greater number of fish in this site.; The study results show that plant growth form influences patterns of food resource use by a littoral fish. Thus, the dynamics of fish populations may be explained, in part, by variation in littoral plant growth forms. Further, this study provides a basis for new questions concerning the unexplored relationship between plant community structure and fish community structure in littoral habitats.