Seawater carbonate chemistry and physiological and mechanical properties of the starfish Asterias rubens in a laboratory experiment

The increase in atmospheric CO2 due to anthropogenic activity results in an acidification of the surface waters of the oceans. Its impact will depend on the considered organisms and ecosystems. The intertidal may harbor organisms pre-adapted to the upcoming changes as they face tidal pH and temperature fluctuations. However, these environments will be more affected as shallow waters will face the highest decrease in seawater pH. In this context, the effects of reduced environmental pH on the physiology and tube feet mechanical properties of the intertidal starfish Asterias rubens, a top predator, were investigated during 15 and 27 days. A. rubens showed a respiratory acidosis with its coelomic fluid pH always lower than that of seawater. This acidosis was most pronounced at pH 7.4. Notwithstanding, the starfish showed no significant variations in RNA/DNA ratio of different tissues and in tube feet strength. However, respiration rates were significantly lower for individuals maintained at reduced seawater pH. Within the ocean acidification context, the present results suggest that A. rubens withstands the effects of reduced seawater pH, at least for medium term exposures.

人类活动引发大气二氧化碳浓度升高，进而造成海洋表层水体酸化。该过程的生态效应因研究涉及的生物类群与生态系统类型有所差异。潮间带生境或可栖息有预先适应未来环境变化的生物——这类生物本就会遭遇潮汐驱动的pH与温度波动。然而，潮间带作为浅水环境，会面临海水pH的最大幅度下降，因此受海洋酸化的影响将更为显著。在此研究背景下，本研究针对潮间带顶级捕食者赭石海星（Asterias rubens），开展了为期15天与27天的暴露实验，探究环境pH降低对其生理状态与管足（tube feet）机械特性的影响。结果显示，赭石海星出现呼吸性酸中毒现象，其体腔液pH始终低于海水pH，且该酸中毒在pH7.4的环境中表现最为显著。尽管如此，海星不同组织的RNA/DNA比值以及管足强度均未出现显著变化，但在海水pH降低的环境中饲养的个体，其呼吸速率显著下降。综上，在海洋酸化的背景下，本研究结果表明赭石海星至少可在中长期暴露实验中耐受海水pH降低带来的影响。