Body-size distribution, biomass estimates and life histories of common insect taxa associated with a submerged macrophyte Lagarosiphon ilicifolius in the Sanyati Basin, Lake Kariba, Zimbabwe

Abstract

The body-size distributions and biomass estimates of Caenis (Ephemeroptera: Caenidae), Cloeon (Ephemeroptera: Baetidae), Coenagrionidae (Odonata), Micronecta (Hemiptera: Corixidae), Chironominae (Diptera: Chironomidae) and Orthocladiinae (Diptera: Chironomidae), the most common and abundant insect taxa associated with a submerged macrophyte Lagarosiphon ilicifolius in Lake Kariba, are presented. Caenis has a univoltine life cycle, whilst Cloeon, Coenagrionidae, Chironominae and Orthocladiinae have multivoltine life cycles. Growth and reproduction of Micronecta occurred all year round. The Coenagrionidae had the highest mean biomass, which was significantly greater than those of the other taxa. Caenis and Orthocladiinae were sensitive to variations in water temperature and dissolved oxygen (DO) concentration, their highest biomasses occurring when temperatures were low and DO concentrations high. The biomasses of Chironominae and Orthocladiinae increased with rising water levels, but that of Caenis decreased. Total insect biomass was minimally affected by variations in water physico-chemical variables. The study suggests that water temperature, water level and DO concentration do have an effect on the biomasses of some insect taxa associated with Lagarosiphon in Lake Kariba. Mixing processes during de-stratification also affect the abundance and biomass of the insect taxa.