Ocean acidification alters the response of intertidal snails to a key sea star predator

Organism-level effects of ocean acidification (OA) are well recognized. Less understood are OA's consequences for ecological species interactions. Here, we examine a behaviourally mediated predator–prey interaction within the rocky intertidal zone of the temperate eastern Pacific Ocean, using it as a model system to explore OA's capacity to impair invertebrate anti-predator behaviours more broadly. Our system involves the iconic sea star predator, Pisaster ochraceus, that elicits flee responses in numerous gastropod prey. We examine, in particular, the capacity for OA-associated reductions in pH to alter flight behaviours of the black turban snail, Tegula funebralis, an often-abundant and well-studied grazer in the system. We assess interactions between these species at 16 discrete levels of pH, quantifying the full functional response of Tegula under present and near-future OA conditions. Results demonstrate the disruption of snail anti-predator behaviours at low pH, with decreases in the time individuals spend in refuge locations. We also show that fluctuations in pH, including those typical of rock pools inhabited by snails, do not materially change outcomes, implying little capacity for episodically benign pH conditions to aid behavioural recovery. Together, these findings suggest a strong potential for OA to induce cascading community-level shifts within this long-studied ecosystem.

海洋酸化（Ocean Acidification, OA）对生物体层面的影响已得到广泛认知，但人们对OA在生态物种相互作用方面的影响仍知之甚少。本研究以温带东太平洋岩石潮间带中的行为介导型捕食者-猎物相互作用为模型体系，旨在探究OA更广泛地损害无脊椎动物反捕食行为的能力。
本研究体系包含标志性海星捕食者Pisaster ochraceus，该物种可诱发多种腹足类猎物产生逃逸反应。我们重点考察了OA相关的pH降低能否改变黑色钟螺（Tegula funebralis）的逃逸行为——该螺类是本体系中常见且被充分研究的牧食者。我们在16个离散pH梯度下开展了上述两个物种间的相互作用实验，量化了当前及近未来OA条件下黑色钟螺的完整功能响应。
实验结果表明，低pH环境会破坏螺类的反捕食行为，表现为个体在庇护场所停留的时间缩短。我们还发现，pH波动（包括螺类栖息的岩石池典型pH波动）不会对实验结果产生实质性影响，这意味着间歇性温和pH条件几乎无法帮助螺类恢复其反捕食行为。
综合来看，这些研究结果表明，OA极有可能在这个被长期研究的潮间带生态系统中引发级联式群落结构变化。