Toxicant exposure increases threshold food levels in freshwater rotifer populations

Abstract

Food limitation and toxicant stress may be important community structuring factors in zooplankton such as rotifers. We hypothesized that food limitation increases rotifer sensitivity to toxicants as measured with a standard two day population growth test and that toxicant stressors shift population growth thresholds, potentially altering competitive relationships. Population growth rates of the rotifer Brachionus calyciflorus were determined at high (18.3 mg of the green alga Nannochloris oculata dry weight per liter) and low (1.83 mg/L) food levels under mercury or pentachlorophenol toxicant stress. Rotifer sensitivity to toxicant stress was increased by as much as 7 times when populations were exposed to toxicants at the low versus high food level. Rotifer populations required up to 6 times as much food to maintain their size when exposed to a toxicant concentration causing no statistically significant reduction in r (NOEC).