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Life history responses of Daphnia similoides simultaneously exposed to microcystin‐LR and ammonia and their post‐exposure recovery

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Aquatic organisms often suffer episodic stress from cyanobacterial bloom‐derived concomitant and sometimes interactive stressors, and may recover when stressors terminate. To assess whether exposed Daphnia can quickly recover from combined toxicity of bloom‐derived stressors, we exposed Daphnia similoides to mixtures of ammonia (0, 0.37, and 0.58 mg L−1) and dissolved microcystin‐LR (0, 10, 30, and 100 µg L−1) in a full factorial design for fourteen days and subsequently allowed them to recover for seven days. During the exposure, we observed that the mixtures of ammonia and microcystin‐LR showed different effects on the selected variables. Ammonia delayed the time to maturation, but microcystin‐LR was not negative to the development of the tested daphnids. Furthermore, microcystin‐LR reduced the prolonged developmental time to first eggs and first clutch caused by high ammonia. The total reproduction of D. similoides was dramatically reduced by 64%∼79% by both toxicants and their combinations, but there were no interactive effects. After the recovery period, most treatments did not recover completely from the combined stress but showed positive signs of recovery, based on the size of the last clutch and the mean number of clutches during recovery, thus the affected D. similoides has the potential to quickly recover from the combined toxic stressors. Environ Toxicol Chem © 2014 SETAC

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