Seasonal dynamics and productivity of Tanytarsus barbitarsis Freeman (Diptera: Chironomidae) in the benthos of a shallow, saline lake

Abstract

The chironomid Tanytarsus barbitarsis is the only abundant benthic species in Lake Werowrap, western Victoria, a small, shallow, highly alkaline lake in which high, fluctuating salinities (c. 36-56 g/l) impose an extremely low biotic diversity. Between successive Octobers in 1969 and 1970, the chironomids passed through about seven generations, attaining numerical densities in excess of 140,000/m². Seasonal fluctuations in density were attributed to emergence, available food, and predation by a dytiscid, Necterosoma penicillatum, occurring in high densities around the rocky marginal areas of the lake. Estimated annual net production, exclusive of mortality and first and second instar biomass, amounted to about 320 kcal/m²/yr. This is perhaps the highest estimate recorded for an inland aquatic macrobenthos community; it is especially remarkable in that evidence from salinity tolerance experiments suggests that the lake is not an optimal environment for the species.