Seawater carbonate chemistry and Ruditapes decussatus biological processes during experiments, 2011

We investigated the effects of ocean acidification on juvenile clams Ruditapes decussatus (average shell length 10.24 mm) in a controlled CO2 perturbation experiment. The carbonate chemistry of seawater was manipulated by diffusing pure CO2, to attain two reduced pH levels (by -0.4 and -0.7 pH units), which were compared to unmanipulated seawater. After 75 days we found no differences among pH treatments in terms of net calcification, size or weight of the clams. The naturally elevated total alkalinity of local seawater probably contributed to buffer the effects of increased pCO2 and reduced pH. Marine organisms may, therefore, show diverse responses to ocean acidification at local scales, particularly in coastal, estuarine and transitional waters, where the physical-chemical characteristics of seawater are most variable. Mortality was significantly reduced in the acidified treatments. This trend was probably related to the occurrence of spontaneous spawning events in the control and intermediate acidification treatments. Spawning, which was unexpected due to the small size of the clams, was not observed for the pH -0.7 treatment, suggesting that the increased survival under acidified conditions may have been associated with a delay in the reproductive cycle of the clams. Future research about the impacts of ocean acidification on marine biodiversity should be extended to other types of biological and ecological processes, apart from biological calcification.本研究通过受控CO₂扰动实验，探究了海洋酸化对幼体文蛤（Ruditapes decussatus，平均壳长10.24 mm）的影响。研究通过通入纯CO₂调控海水碳酸盐化学体系，设置了两个pH降低梯度（分别下降0.4和0.7个pH单位），并以未调控的天然海水作为对照组。实验持续75天后，各组pH处理下的文蛤净钙化率、个体规格与体重均无显著差异。本地海水天然偏高的总碱度，可能缓冲了pCO₂升高与pH降低带来的影响。因此，海洋生物在局地尺度下对海洋酸化的响应可能存在显著差异，在物理化学特征波动最为剧烈的近岸、河口与过渡性水域中这一现象尤为突出。酸化处理组的文蛤死亡率显著降低，这一现象可能与对照组与中度酸化处理组中出现的自然产卵事件相关。由于文蛤个体偏小，自然产卵本属意外现象，但pH下降0.7个单位的处理组并未观测到产卵行为，这表明酸化条件下存活率的提升，可能与文蛤生殖周期的延迟有关。未来有关海洋酸化对海洋生物多样性影响的研究，除生物钙化过程外，还应拓展至其他类型的生物与生态过程。