Populations of Pacific Oysters Crassostrea gigas Respond Variably to Elevated CO2 and Predation by Morula marginalba

Ocean acidification is anticipated to decrease calcification and increase dissolution of shelled molluscs. Molluscs with thinner and weaker shells may be more susceptible to predation, but not all studies have measured negative responses of molluscs to elevated pCO2. Recent studies measuring the response of molluscs have found greater variability at the population level than first expected. Here we investigate the impact of acidification on the predatory whelk Morula marginalba and genetically distinct subpopulations of the Pacific oyster Crassostrea gigas. Whelks and eight family lines of C. gigas were separately exposed to ambient (385 ppm) and elevated (1000 ppm) pCO2 for 6 weeks. Following this period, individuals of M. marginalba were transferred into tanks with oysters at ambient and elevated pCO2 for 17 days. The increase in shell height of the oysters was on average 63% less at elevated compared to ambient pCO2. There were differences in shell compression strength, thickness, and mass among family lines of C. gigas, with sometimes an interaction between pCO2 and family line. Against expectations, this study found increased shell strength in the prey and reduced shell strength in the predator at elevated compared to ambient pCO2. After 10 days, the whelks consumed significantly more oysters regardless of whether C. gigas had been exposed to ambient or elevated CO2, but this was not dependent on the family line and the effect was not significant after 17 days. Our study found an increase in predation after exposure of the predator to predicted near-future levels of estuarine pCO2.

海洋酸化预计将降低带壳软体动物的钙化速率，并加剧其壳体的溶解过程。壳体更薄更脆弱的软体动物可能更易遭受捕食，但并非所有研究都观测到了软体动物对升高的二氧化碳分压(pCO2)产生的负面响应。近期针对软体动物响应的研究发现，种群水平上的变异程度远超最初预期。本研究探讨了酸化对掠食性蛾螺（Morula marginalba）以及太平洋牡蛎（Crassostrea gigas）遗传分化亚群的影响。研究人员将蛾螺与8个太平洋牡蛎（C. gigas）家系分别置于环境水平(385 ppm)与升高水平(1000 ppm)的二氧化碳分压环境中暴露6周。暴露结束后，将蛾螺个体转移至搭载有牡蛎的养殖箱中，分别维持在环境与升高的二氧化碳分压环境中17天。与环境二氧化碳分压组相比，升高组牡蛎的壳高平均增长量降低了63%。太平洋牡蛎（C. gigas）不同家系间的壳体抗压强度、厚度及重量存在显著差异，且二氧化碳分压与家系间有时存在交互效应。与预期相悖的是，本研究发现，相较于环境二氧化碳分压组，升高组的猎物（牡蛎）壳体强度有所提升，而捕食者（蛾螺）的壳体强度则出现下降。暴露10天后，无论太平洋牡蛎（C. gigas）曾处于环境还是升高的二氧化碳分压环境中，蛾螺的捕食量均显著提升，但该效应并不依赖于牡蛎家系，且在17天后该效应不再显著。本研究证实，当捕食者暴露于预测的近未来河口二氧化碳分压水平时，其捕食行为会出现增强。