Seawater carbonate chemistry and sea urchin Paracentrotus lividus biological processes during experiments, 2011

Ocean acidification is predicted to have significant effects on benthic calcifying invertebrates, in particular on their early developmental stages. Echinoderm larvae could be particularly vulnerable to decreased pH, with major consequences for adult populations. The objective of this study was to understand how ocean acidification would affect the initial life stages of the sea urchin Paracentrotus lividus, a common species that is widely distributed in the Mediterranean Sea and the NE Atlantic. The effects of decreased pH (elevated PCO2) were investigated through physiological and molecular analyses on both embryonic and larval stages. Eggs and larvae were reared in Mediterranean seawater at six pH levels, i.e. pHT 8.1, 7.9, 7.7, 7.5, 7.25 and 7.0. Fertilization success, survival, growth and calcification rates were monitored over a 3 day period. The expression of genes coding for key proteins involved in development and biomineralization was also monitored. Paracentrotus lividus appears to be extremely resistant to low pH, with no effect on fertilization success or larval survival. Larval growth was slowed when exposed to low pH but with no direct impact on relative larval morphology or calcification down to pHT 7.25. Consequently, at a given time, larvae exposed to low pH were present at a normal but delayed larval stage. More surprisingly, candidate genes involved in development and biomineralization were upregulated by factors of up to 26 at low pH. Our results revealed plasticity at the gene expression level that allows a normal, but delayed, development under low pH conditions.

海洋酸化被预测会对底栖钙化无脊椎动物（benthic calcifying invertebrates）产生显著影响，尤其作用于其早期发育阶段。棘皮动物幼虫（Echinoderm larvae）可能对pH降低特别敏感，这将对成体种群造成重大后果。本研究旨在探究海洋酸化如何影响紫球海胆（Paracentrotus lividus）的初始生命阶段——该物种为地中海及东北大西洋广泛分布的常见种类。

通过对胚胎及幼虫阶段的生理与分子分析，研究考察了pH降低（即PCO₂升高）的影响。卵与幼虫在六个pH水平（pHT 8.1、7.9、7.7、7.5、7.25及7.0）的地中海海水中培养。在3天周期内，监测受精成功率、存活率、生长速率及钙化率；同时分析参与发育及生物矿化（biomineralization）的关键蛋白编码基因的表达情况。

紫球海胆（Paracentrotus lividus）对低pH表现出极强抗性：低pH对其受精成功率或幼虫存活率无显著影响。暴露于低pH环境下的幼虫生长速率减缓，但在pHT 7.25及以上水平时，幼虫相对形态或钙化未受直接影响。因此，在特定时间点，低pH暴露组的幼虫处于正常但延迟的发育阶段。更令人意外的是，参与发育及生物矿化的候选基因在低pH条件下上调幅度可达26倍。本研究结果揭示，基因表达层面的可塑性（plasticity）使该物种能在低pH环境中维持正常但延迟的发育过程。