Ocean acidification increases copper toxicity differentially in two key marine invertebrates with distinct acid-base responses.

Ceri Lewis,Robert P Ellis,Rod W Wilson,Emily Vernon,Sam Newbatt,Katie Elliot

doi:10.1038/srep21554

Abstract

Ocean acidification (OA) is expected to indirectly impact biota living in contaminated coastal environments by altering the bioavailability and potentially toxicity of many pH-sensitive metals. Here, we show that OA (pH 7.71; pCO2 1480 μatm) significantly increases the toxicity responses to a global coastal contaminant (copper ~0.1 μM) in two keystone benthic species; mussels (Mytilus edulis) and purple sea urchins (Paracentrotus lividus). Mussels showed an extracellular acidosis in response to OA and copper individually which was enhanced during combined exposure. In contrast, urchins maintained extracellular fluid pH under OA by accumulating bicarbonate but exhibited a slight alkalosis in response to copper either alone or with OA. Importantly, copper-induced damage to DNA and lipids was significantly greater under OA compared to control conditions (pH 8.14; pCO2 470 μatm) for both species. However, this increase in DNA-damage was four times lower in urchins than mussels, suggesting that internal acid-base regulation in urchins may substantially moderate the magnitude of this OA-induced copper toxicity effect. Thus, changes in metal toxicity under OA may not purely be driven by metal speciation in seawater and may be far more diverse than either single-stressor or single-species studies indicate. This has important implications for future environmental management strategies.

Highlights

Ocean acidification (OA) is expected to indirectly impact biota living in contaminated coastal environments by altering the bioavailability and potentially toxicity of many pH-sensitive metals
Haemolymph bicarbonate levels (HCO3−) in mussels showed a similar pattern of change in response to this elevated pCO2 (Fig. 1b), with a small but significant increase of ~0.2 mM under OA conditions and about double this increase when exposed to copper alone (Fig. 1b; two-way GLM model for OA F1,39 = 9.75, P = 0.004; for copper F1,39 = 26.57, P < 0.001; interaction term F1,39 = 1.95, P = 0.171)
We found that for both mussels (Mytilus edulis) and urchins (Paracentrotus lividus) copper-induced damage to DNA was significantly greater when animals were exposed to nominal 0.1 μ M copper under OA conditions compared with animals exposed under extant pCO2 levels

Summary

Introduction

Ocean acidification (OA) is expected to indirectly impact biota living in contaminated coastal environments by altering the bioavailability and potentially toxicity of many pH-sensitive metals. We show that OA (pH 7.71; pCO2 1480 μatm) significantly increases the toxicity responses to a global coastal contaminant (copper ~0.1 μM) in two keystone benthic species; mussels (Mytilus edulis) and purple sea urchins (Paracentrotus lividus). Changes in metal toxicity under OA may not purely be driven by metal speciation in seawater and may be far more diverse than either single-stressor or single-species studies indicate This has important implications for future environmental management strategies. Increased metal accumulation under near-future OA conditions has been demonstrated for two bivalves species so far[27] and for marine organisms exposed to the same nominal concentrations of any metal, greater metal toxicity effects would be predicted under near-future OA where reduced seawater pH increases free ion availability

Methods

Results

Conclusion