Effect of ocean acidification on growth, gonad development and physiology of the sea urchin Hemicentrotus pulcherrimus

Ocean acidification, due to diffusive uptake of atmospheric CO2, has potentially profound ramifications for the entire marine ecosystem. Scientific knowledge on the biological impacts of ocean acidification is rapidly accumulating; however, data are still scarce on whether and how ocean acidification affects the reproductive system of marine organisms. We evaluated the long-term (9 mo) effects of high CO2 (1000 μatm) on the gametogenesis, survival, growth and physiology of the sea urchin Hemicentrotus pulcherrimus. Hypercapnic exposure delayed gonad maturation and spawning by 1 mo, whereas it had no effect on the maximum number of ova, survival or growth. After 9 mo of exposure, pH (control: 7.61, high-CO2: 7.03) and Mg2+ concentration (control: 50.3, high-CO2: 48.6 mmol l−1) of the coelomic fluid were significantly lower in the experimental urchins. In addition, a 16 d exposure experiment revealed that 1000 μatm CO2 suppressed food intake to <30% of that of the controls. These data suggest that the ocean condition predicted to occur by the end of this century disrupts the physiological status of the sea urchin, possibly through reduced energy intake, which may delay reproductive phenology of the species. Taking into account earlier studies reporting negative impacts of ocean acidification on the early development of the same species, these results imply that ocean acidification will threaten H. pulcherrimus at a community level.