Noisette Fanny, Comtet Thierry, Legrand Erwann, Bordeyne François, Davoult Dominique, Martin Sophie
Sorbonne Universités, UPMC Univ. Paris 06, UMR 7144, Station Biologique de Roscoff, Roscoff, France; CNRS, UMR 7144, Station Biologique de Roscoff, Roscoff, France.
PLoS One. 2014 Mar 26;9(3):e93021. doi: 10.1371/journal.pone.0093021. eCollection 2014.
Early life history stages of marine organisms are generally thought to be more sensitive to environmental stress than adults. Although most marine invertebrates are broadcast spawners, some species are brooders and/or protect their embryos in egg or capsules. Brooding and encapsulation strategies are typically assumed to confer greater safety and protection to embryos, although little is known about the physico-chemical conditions within egg capsules. In the context of ocean acidification, the protective role of encapsulation remains to be investigated. To address this issue, we conducted experiments on the gastropod Crepidula fornicata. This species broods its embryos within capsules located under the female and veliger larvae are released directly into the water column. C. fornicata adults were reared at the current level of CO2 partial pressure (pCO2) (390 μatm) and at elevated levels (750 and 1400 μatm) before and after fertilization and until larval release, such that larval development occurred entirely at a given pCO2. The pCO2 effects on shell morphology, the frequency of abnormalities and mineralization level were investigated on released larvae. Shell length decreased by 6% and shell surface area by 11% at elevated pCO2 (1400 μatm). The percentage of abnormalities was 1.5- to 4-fold higher at 750 μatm and 1400 μatm pCO2, respectively, than at 390 μatm. The intensity of birefringence, used as a proxy for the mineralization level of the larval shell, also decreased with increasing pCO2. These negative results are likely explained by increased intracapsular acidosis due to elevated pCO2 in extracapsular seawater. The encapsulation of C. fornicata embryos did not protect them against the deleterious effects of a predicted pCO2 increase. Nevertheless, C. fornicata larvae seemed less affected than other mollusk species. Further studies are needed to identify the critical points of the life cycle in this species in light of future ocean acidification.
海洋生物的早期生活史阶段通常被认为比成体对环境压力更敏感。尽管大多数海洋无脊椎动物是体外产卵者，但有些物种是育幼者和/或在卵或卵囊中保护它们的胚胎。育幼和包囊化策略通常被认为能为胚胎提供更大的安全性和保护，尽管人们对卵囊内的物理化学条件知之甚少。在海洋酸化的背景下，包囊化的保护作用仍有待研究。为了解决这个问题，我们对腹足纲动物福氏盘螺进行了实验。该物种在位于雌体下方的卵囊中育幼其胚胎，而面盘幼虫直接被释放到水柱中。在受精前后以及直至幼虫释放，将福氏盘螺成体饲养在当前的二氧化碳分压（pCO₂）水平（390微巴）以及升高的水平（750和1400微巴）下，使得幼虫发育完全在给定的pCO₂水平下进行。研究了pCO₂对释放出的幼虫的壳形态、异常频率和矿化水平的影响。在升高的pCO₂（1400微巴）下，壳长减少了6%，壳表面积减少了11%。在750微巴和1400微巴pCO₂下，异常百分比分别比在390微巴时高1.5至4倍。用作幼虫壳矿化水平指标的双折射强度也随着pCO₂的升高而降低。这些负面结果可能是由于囊外海水中pCO₂升高导致囊内酸中毒加剧所致。福氏盘螺胚胎的包囊化并不能保护它们免受预计的pCO₂升高的有害影响。然而，福氏盘螺幼虫似乎比其他软体动物物种受影响更小。鉴于未来的海洋酸化，需要进一步研究来确定该物种生命周期中的关键点。
