High concentration of Phaeocystis globosa reduces the sensitivity of rotifer Brachionus plicatilis to cadmium: Based on an exponential approach fitting the changes in some key life-history traits

Abstract

Most coastal waters are at risk of heavy metal pollution, and the biomass of primary producer phytoplankton always fluctuates, which usually causes zooplankton to be exposed in different concentrations of food and heavy metal. Phytoplankton abundance and heavy metal may interact on zooplankton. Therefore, to assess the definite interactive way, in this study we investigated the combined effects of different cadmium (Cd) levels and Phaeocystis globosa concentrations on some key life-history traits of the rotifer Brachionus plicatilis. Results showed that the Cd level and P. globosa concentration had a significant interaction on the key life-history parameters of the rotifer. Mid-level algal concentrations (5–36 × 104 cells mL−1) had an apparent effect on brood production and the number of rotifers producing offspring at high Cd level. The time to first reproduction exponentially decreased with increasing P. globosa concentrations under any Cd levels and then subsequently reached a constant value. With increasing P. globosa concentration, the total number of offspring exponentially increased and then reached the asymptotic value; the survival time under any Cd levels exponentially decreased with the increasing P. globosa concentration and subsequently tended to be a constant value. Without Cd, the low P. globosa concentration only decreased the reproduction of rotifers. However, the extreme low P. globosa concentration (1–3 × 104 cells mL−1) under higher Cd level (0.0354 mM) completely inhibited the reproduction and also shorten the survival time. Higher Cd level decreased the asymptotic total offspring per rotifer and survival time. High concentration of P. globosa can reduce the sensitivity of rotifer to heavy metal. However, the negative effects could not be eliminated completely by the increasing P. globosa concentration. The findings indicated that ecotoxicological studies on the toxicity of heavy metal need to consider the effects of food concentrations, which contributes to understanding the diverse tolerance of zooplankton to heavy metals.