The ecological energetics of the net-spinning caddisfly, Hydropsyche venularis Banks (Trichoptera: Hydropsychidae)

The study of organism level energetics in conjunction with ecosystem level energetics can lead to a better understanding of the structure and function of stream ecosystems. The purpose of this study was to calculate energy budget equations for a net-spinning caddisfly, Hydropsyche venularis Banks, and to develop, or modify, methods used to determine consumption and growth in the field. The method used to determine consumption rate was a modification of the procedure used by Ladle et al. (1972). Growth rate was determined by mark-recapture and metabolic rate was determined in a Gilson respirometer. Egestion rate was determined by a new method.

Consumption rate was found to be higher than other values reported for hydropsychids. Growth and metabolic rate were similar to that reported by McCullough et al. (1979) for H. occidentalis. Egestion was much lower than would be predicted from consumption and cast doubt as to the usefulness of the new method. Energy budgets were calculated from regression equations relating the various processing rates to body weight and temperature for 1, 8, and 15 mg larvae at 15 to 25°C. The overall energy budget was: C - 0.53 cal/mg/hr, G - 0.01 cal/mg/hr, R - 0.01 cal/mg/hr, AE - 8%, NGE - 56%, GGE - 5%. Egestion was constant at 0.01 cal/mg/hr.

The high consumption rate of H. venularis, above that necessary for growth and maintainence may be significant in the processing of energy in Little River. Feces produced by H. venularis are larger than the particles ingested. The fecal pellets are then available to other filter-feeders and deposit feeders. Higher consumption rates may therefore increase the efficiency of the ecosystem.