Competitive outcome between the rotiferBrachionus calyciflorusand the cladoceranMoina macrocopadepends on algal density but not temperature

Abstract

The rotifer Brachionus calyciflorus often occurs simultaneously with the cladoceran Moina macro- copa in tropical water bodies. We studied the effects of temperature (20, 25 and 30 xC) and algal density (0.5, 1.0 and 3.0r 10 6 cells.mL x1 Scenedesmus obliquus) on the outcome of competition and duration of coex- istence between B. calyciflorus and M. macrocopa using population growth experiments. The results showed that regardless of temperature, M. macrocopa outcompeted B. calyciflorus at the lowest algal density (0.5r 10 6 cells.mL x1 ), whereas B. calyciflorus outcompeted M. macrocopa at the higher algal densities (1.0 and 3.0r 10 6 cells.mL x1 ). The duration of coexistence shortened with increasing temperature when M. macrocopa outcompeted B. calyciflorus, and those with increasing temperature and algal density when B. calyciflorus outcompeted M. macrocopa. Our results suggested that the competitive outcome between the rotifer B. calyciflorus and the cladoceran M. macrocopa was dependent on algal density but not temperature, the duration of coexistence between them was dependent on algal density and temperature, and the exploitative competition of M. macrocopa over B. calyciflorus may be more important than the interference competition.