Composition and Productivity of the Benthic Macroinvertebrate Community of a Subtropical Reservoir

Abstract

AbstractPhysical‐chemical conditions, phytoplankton productivity, community structure and productivity of the macroinvertebrate benthic community were determined during 1976–77 in a subtropical reservoir. Physical‐chemical results revealed high nitrate and phosphate concentrations with highest values in the riverine segment. Large phytoplankton populations were present during most of the year. Phytoplankton productivity was high, producing an annual mean of 87 mg C · m−3 · h−1 (12 hours light day). High turbidity in the riverine segment limited phytoplankton productivity during winter and spring. Macrobenthos was dominated by chironomids (Chironomus, Procladius, Coelotanypus and Tanypus) and oligochaetes (Limnodrilus). The annual mean benthic population was estimated at 1,626 · m−2 with a mean dry weight of 0.66 g · m−2. Mean benthic species diversity was 1.80. A lacustrine‐riverine community gradient was revealed. Benthic productivity was 6.8 g · m−2 · yr−1 (dry weight) with a P: B ratio of 10. A low correlation was observed between benthic and phytoplankton productivity, and between phytoplankton standing crop and benthic macroinvertebrate numbers throughout the reservoir. Algal food supplies had little impact on the benthic community which was composed predominately of species which fed mostly on organic detritus. Stressful conditions caused by low dissolved oxygen concentrations probably inhibited development of the benthic community throughout the reservoir during summer months, while high sedimentation rates limited development in the head waters.