The Interactive Effects of Ammonia and Microcystin on Life-History Traits of the Cladoceran Daphnia magna: Synergistic or Antagonistic?

Zhou Yang,Yafen Chen,Kai Lü,David J S Montagnes,Howard Browman

doi:10.1371/journal.pone.0032285

Abstract

The occurrence of Microcystis blooms is a worldwide concern that has caused numerous adverse effects on water quality and lake ecology. Elevated ammonia and microcystin concentrations co-occur during the degradation of Microcystis blooms and are toxic to aquatic organisms; we studied the relative and combined effects of these on the life history of the model organism Daphnia magna. Ammonia and microcystin-LR treatments were: 0, 0.366, 0.581 mg L−1 and 0, 10, 30, 100 µg L−1, respectively. Experiments followed a fully factorial design. Incubations were 14 d and recorded the following life-history traits: number of moults, time to first batch of eggs, time to first clutch, size at first batch of eggs, size at first clutch, number of clutches per female, number of offspring per clutch, and total offspring per female. Both ammonia and microcystin were detrimental to most life-history traits. Interactive effects of the toxins occurred for five traits: the time to first batch of eggs appearing in the brood pouch, time to first clutch, size at first clutch, number of clutches, and total offspring per female. The interactive effects of ammonia and microcystin appeared to be synergistic on some parameters (e.g., time to first eggs) and antagonistic on others (e.g., total offspring per female). In conclusion, the released toxins during the degradation of Microcystis blooms would result, according to our data, in substantially negative effect on D. magna.

Highlights

Cyanobacterial blooms occur worldwide in eutrophic lakes and reservoirs [1]
Number of moults decreased with increasing ammonia concentration under mid-dose microcystin conditions (Figure 1b– c), whereas the presence of microcystin increased number of moults under any ammonia concentrations, even significant effects were detected in some microcystin concentrations (Figure 1e–g)
The interactive effects of ammonia and microcystin occurred for most of the life-history traits; i.e. of the eight traits examined, interactive effects of microcystin and ammonia occurred for five (Table 1): time to first batch of eggs appearing in the brood pouch, time to first clutch, size at first clutch, number of clutches, and total offspring per female

Summary

Introduction

Cyanobacterial blooms occur worldwide in eutrophic lakes and reservoirs [1]. In a few cases, microcystin levels be .1800 mg L21 when toxins are released into water after lysis of cyanobacterial cells, during the collapse of heavy blooms [12,13]. These observations of high levels, which may become more common as cyanobacterial blooms increase in frequency and become more pronounced [4], stimulated us to examine a range of concentrations that include extremely high concentrations. Microcystin inhibits feeding, reduces growth, and increases mortality in cladocerans [17,18,19,20], and in particular, the variant microcystin-LR exerts strong toxic effects on Daphnia [18,21,22,23,24,25,26]

Methods

Results

Discussion

Conclusion