Acidification alters predator-prey interactions of blue crab Callinectes sapidus and soft-shell clam Mya arenaria

Acidification due to anthropogenic CO2 pollution, along with episodic or persistent acidification that occurs in coastal environments, will likely result in severe seasonal acidification in estuarine environments. Acidification decreases the fitness of individual species, but the degree to which predator-prey interactions will be impacted is largely unknown. This mesocosm study examined the effect of CO2 acidification on crab-bivalve predator-prey interactions involving two commercially important Chesapeake Bay species, the blue crab Callinectes sapidus and the soft-shell clam Mya arenaria. In particular, the direct effects of CO2 acidification on clam growth and behavior, and the indirect effects of CO2 acidification on interactions between crabs and clams were examined. Mya arenaria were grown in CO2-acidified water (pH 7.2) or ambient conditions (pH 7.8) for 30 days. To determine the effect of acidification on clam responsiveness to mechanical disturbance, a probe was slowly moved towards clams until they ceased pumping (a behavior to avoid detection by predators), and the distance between the probe and the clam's siphon was noted. Clams were exposed to predation by C. sapidus, which were held under acidified or ambient conditions for 48 h. Callinectes sapidus handling time, search time, and encounter rate were measured from video. Acidified clams had lighter shells than ambient clams, indicating that shell dissolution occurred. Acidification reduced the responsiveness of M. arenaria to a mechanical disturbance that simulated an approaching predator. As compared to ambient trials, crabs in acidified trials had higher encounter rates; however, this was offset by crabs taking longer to find the first clam in trials, and by increased occurrence of crabs eating only a portion of the prey available. As a result, there was no net change in predation-related clam mortality in acidified trials as compared to ambient conditions. Understanding how acidification will impact food webs in productive estuarine environments requires an examination of the direct impacts of acidification on organism behavior and physiology, as well as indirect effects of acidification mediated through predator-prey interactions.

人为二氧化碳污染引发的酸化，加之沿海环境中出现的间歇性或持续性酸化，大概率会导致河口环境出现严重的季节性酸化。酸化会降低单个物种的适合度，但捕食者-猎物相互作用受酸化影响的程度在很大程度上仍不明确。本中型实验生态系（mesocosm）研究探究了二氧化碳酸化对蟹类-双壳类捕食者-猎物相互作用的影响，研究对象为切萨皮克湾两种具有重要商业价值的物种：蓝蟹（Callinectes sapidus）与软壳蛤（Mya arenaria）。具体而言，本研究同时考察了二氧化碳酸化对蛤类生长与行为的直接影响，以及酸化通过蟹类与蛤类间相互作用产生的间接影响。将软壳蛤置于二氧化碳酸化水体（pH 7.2）或自然环境水体（pH 7.8）中培养30天。为明确酸化对蛤类机械扰动响应能力的影响，研究人员将探针缓慢移向蛤类，直至其停止喷水（该行为用于躲避捕食者的侦测），并记录探针与蛤类虹吸管之间的距离。将蛤类暴露于蓝蟹的捕食环境中，而蓝蟹此前已在酸化或自然环境中培育48小时。通过视频录像测算蓝蟹的处理时间、搜寻时间与相遇率。酸化组蛤类的贝壳较自然组更轻，表明发生了贝壳溶解现象。酸化会降低软壳蛤对模拟捕食者逼近的机械扰动的响应能力。与自然组实验相比，酸化组实验中的蟹类相遇率更高，但这一优势被抵消：实验中蟹类搜寻首只蛤类的耗时更长，且蟹类仅捕食部分可用猎物的情况更为频发。因此，与自然环境条件相比，酸化组实验中与捕食相关的蛤类死亡率并无净变化。若要明晰酸化将如何影响高生产力河口环境中的食物网，需同时考察酸化对生物行为与生理的直接影响，以及通过捕食者-猎物相互作用介导的酸化间接效应。