Combined Effects of Food (Chlorella vulgaris) Concentration and Temperature on the Population Growth of Brachionus havanaensis (Rotifera: Brachionidae)

Abstract

ABSTRACT Brachionus havanaensis is a common rotifer in the North American continent. Its frequent occurrence in relatively high densities and availability throughout the year in several Mexican freshwater bodies prompted us to understand the population dynamics of this species in relation to food level (Chlorella vulgaris at 0.5X106, 1.0X106 and 2.0X106 cells ml−1) and temperature (15°, 20°, and 25°C). We found that regardless of the temperature, an increase in food level resulted in an increase in the population growth of the rotifers. However, at any food level, rotifers cultured at 15°C did not increase beyond 8 ind. ml−1; on the other hand at comparable food concentrations at both 20 and 25°C, the population densities were higher than 600 ind. ml−1. The rate of population increase per day (d−1) of B. havanaensis varied from 0.02 to 0.29 d−1 depending on the food density and temperature. Our results also showed that regardless of the food level, at 15°C B. havanaensis had no statistically significant relation between the number of eggs per female and the population abundance. On the other hand, significant inverse relationships were observed between the egg ratio and population density of B. havanaensis grown at 20° and 25°C, regardless of the food level. When the daily growth rates were plotted against the population densities of the previous day, we found a significantly inverse relation for rotifers grown at 20° and 25°C, but not at 15°C, for all tested food levels. There were statistically significant effects of food level, temperature, and the interaction of both parameters on both the peak population density and the rate of population increase, although temperature had a far greater influence than did food.