BIOENERGETIC RELATIONS IN SUBMERGED AQUATIC VEGETATION - AN EXPERIMENTAL TEST OF PREY USE BY JUVENILE BLUEGILLS

We experimentally tested the hypotheses that bluegills in vegetated ha bitats grow more rapidly than in nonvegetated habitats because (1) veg etated habitats contain a greater caloric density and (2) are less sus ceptible to energetic depletion. The 10-week experiment was conducted in enclosures containing factorial combinations of the presence or abs ence of Vallisneria americana and juvenile bluegills Lepomis macrochir us. After 6 weeks, Vallisneria-only treatments contained a mean of 104 8 cal/m(2) in the benthos, whereas treatments with both Vallisneria an d bluegills contained 610 cal/m(2). Hyalella azteca, a preferred prey of bluegill, were nearly depleted in nonvegetated enclosures, whereas Hyalella densities in enclosures with Vallisneria were much less effec ted by fish. Bluegill growth was significantly greater with Vallisneri a than without but declining water temperatures after week 6 resulted in slower growth despite abundant prey. Ultimately, growth of bluegill resulted from an interaction between availability and ingestion of pr ey, and water temperature.