Effects of ocean acidification on toxicity of two trace metals in two marine molluscs in their early life stages

Abstract

Ocean acidification (OA) is usually thought to change the speciation of trace metals and increase the concentration of free metal ions, hence elevating metal bioavailability. In this study, embryos of the oyster Crassostrea angulata and abalone Haliotis discus hannai were cultured under 4 pCO2 conditions (400, 800, 1500 and 2000 µatm) with Cu and Zn added. Fertilization rate was measured 2 h post-fertilization (hpf), while larval deformation and larval shell length were measured 24 hpf. Our results show that OA can alleviate Cu and Zn inhibition of C. angulata fertilization by 86.1 and 26.4% respectively, and Zn inhibition of H. discus hannai fertilization by 43.7%. However, OA enhanced the inhibitory effect of Cu on fertilization of H. discus hannai by 34.7%. OA enhanced the toxic effect of Cu on larval normality of C. angulata by 22.0% and the effect of Cu and Zn on larval normality of H. discus hannai by 71.4 and 37.2%, respectively. OA also enhanced the inhibitory effects of Cu and Zn on larval calcification in H. discus hannai by 8.8 and 8.6%, respectively. However, OA did not change the effect of Cu on the calcification of C. angulata larvae. OA decreased Zn inhibition of oyster larval calcification from 3.1 to 1.5%. Based on our results, the toxic effects of metal on early development of molluscs are not always increased by rising pCO2 and differ across developmental stages, egg structure and species. This complexity suggests that caution should be taken when carrying out multiple environmental stressor tests on molluscan embryos.