Effect of algal food (Chlorella vulgaris) concentration and inoculation density on the competition among three planktonic Brachionidae (Rotifera: Monogononta)

Abstract

Competitive outcomes among three rotifer species (Anuraeopsis fissa, Brachionus havanaensis and B. angularis) were quantified with different inoculation densities of two competing species at a time (0, 25, 50, 75 and100%) and using different algal (Chlorella vulgaris) densities (0.2 × 106 , 0.4 × 106 and 0.8 × 106 cells ml-1). In control cultures, when each species was grown alone, the population growth of rotifers increased with increasing food availability in the medium, but in mixed cultures, decreased with increasing proportion of the competing species. At low food level, compared to B. havanaensis, B. angularis had stronger negative impact on A. fissa. However, with increasing algal density, both species of Brachionus had similar but reduced impact on A. fissa. Population growth of B. havanaensis was more adversely affected by A. fissa than B. angularis at low and intermediate concentrations. At high food level, the impact of either A. fissa or B. angularis on the growth of B. havanaensis was similar. When grown alone, for a given food density, A. fissa was more numerically (4 to 6 times) abundant than the other two species. The rate of population increase (r) of rotifers increased with increasing food levels. Depending on the rotifer species and the test conditions, the r varied from -0.001 to 0.34 d-1. Results showed that the competitive outcome in the tested rotifers depended on the initial inoculation density of the competing species, the offered food concentration as well as the interaction of these two factors.