Seawater carbonate chemistry and larval settlement of Sea urchin larvae@en

Extensive research has shown that the early life stages of marine organisms are sensitive to ocean acidification (OA). Less is known, however, on whether larval settlement and metamorphosis may be affected, or by which mechanisms. These are key processes in the life cycle of most marine benthic organisms, since they mark the transition between the free swimming larval stage to the benthic life. We investigated whether OA could affect the larval settlement success of the sea urchin Evechinus chloroticus, a key coastal species with ecological, economic and cultural importance in New Zealand. We performed four settlement experiments to test whether reduced seawater pH (ranging from 8.1 to 7.0, at an interval of ∼0.2 pH units) alters larval settlement and metamorphosis success. Our results show that settlement success was not significantly reduced when the larvae were exposed to a range of reduced seawater pH treatments (8.1–7.0) at time of settlement (direct effects). Similarly, when presented with crustose coralline algae (CCA) pre-conditioned in different seawater pH of either pH 8.1 or 7.7 for 28 days, larval settlement success remained unaltered (indirect effects). We conclude that competent larvae in this species are resilient to OA at time of settlement. Further research on a range of taxa that vary in settlement selectivity and behaviour is needed in order to fully understand the effects of OA on the life cycle of marine invertebrates and the consequences it might have for future coastal marine ecosystems.大量研究证实，海洋生物的早期生命阶段对海洋酸化（OA）具有敏感性。然而，学界对于幼体附着与变态过程是否会受海洋酸化影响，以及具体的作用机制，仍缺乏充分认知。附着与变态是多数海洋底栖生物生命周期的核心环节，标志着浮游幼体阶段向底栖生活的转变。本研究以新西兰本土兼具生态、经济与文化价值的关键近岸物种——海胆（Evechinus chloroticus）为研究材料，探究海洋酸化是否会影响其幼体附着成功率。我们开展4组附着实验，设置梯度为8.1至7.0（间隔约0.2个pH单位）的降pH海水处理组，以检验该处理是否会改变幼体附着与变态成功率。实验结果表明，在幼体附着阶段直接暴露于上述梯度降低的海水pH环境中时，其附着成功率未出现显著下降（直接影响）。同样，当幼体接触经pH 8.1或7.7的海水预培养28天的结壳珊瑚藻（CCA）时，其附着成功率仍未发生显著变化（间接影响）。综上，该物种的具附着能力幼体在附着阶段对海洋酸化具有耐受性。未来需针对不同附着选择性与行为特征的多个生物类群开展进一步研究，以全面阐明海洋酸化对海洋无脊椎动物生命周期的影响，及其对未来近岸海洋生态系统可能造成的后果。