Atlantic Canada’s American oyster (Crassostrea virginica) beds, while economically and ecologically important, have been in decline over the past few decades. Predation by crabs, in particular by the European green crab (Carcinus maenas), has been proposed as one of the potential causes of such decline. Hence, this study examined oyster mortality levels in multiple beds across Prince Edward Island (PEI) and then experimentally assessed the contribution of green crab predation to oyster mortality. Results from surveys conducted in 10 estuaries across PEI in 2014 indicate that the probability of mortality for small oysters was significantly higher when green crabs were present then in areas without green crabs. This probability of mortality was significantly less when there was the presence of alternative prey like natural mussel beds (Mytilus edulis). The odds of oyster mortality were also higher when beds had rock crabs (Cancer irroratus) compared to beds with no rock crabs. Given the potential importance of green crab predation, its influence was assessed in 2015 using two field experiments with tethered oysters. Our results indicate that odds of small oyster mortality occurring were much higher in green crab inclusion cages than in the open environment and the exclusion cages. These results reaffirm that oysters up to ~40 mm SL are vulnerable to predation, and at least some of the mortality affecting these oysters can be causally attributed to green crab predation. Green crab predation rates upon small oysters are relevant given the economic benefits and ecosystem services provided by these bivalves. They highlight the need for the industry to consider mitigation measures and potentially adapt their oyster growing strategies.

中文翻译：

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探索加拿大大西洋沿岸牡蛎床的减少：捕食螃蟹对美国牡蛎的潜在影响（Crassostrea virginica）

加拿大大西洋的美国牡蛎（Crassostrea virginica）床虽然在经济和生态方面都很重要，但在过去的几十年中一直在减少。螃蟹，特别是欧洲绿蟹（Carcinus maenas）的捕食被认为是造成这种下降的潜在原因之一。因此，这项研究检查了爱德华王子岛（PEI）上多张牡蛎的死亡率，然后通过实验评估了绿蟹捕食对牡蛎死亡率的贡献。2014年在PEI的10个河口进行的调查结果表明，当存在绿蟹的情况下，小牡蛎的死亡率显着高于没有绿蟹的地区。当存在天然贻贝（Mytilus edulis）这样的替代猎物时，这种死亡的可能性大大降低。与没有石蟹的河床相比，有石蟹（河蟹）的牡蛎死亡率的几率也更高。考虑到绿蟹捕食的潜在重要性，2015年使用拴系牡蛎进行了两次野外实验，评估了其影响。我们的结果表明，在绿蟹包涵笼中发生小牡蛎死亡的几率比在开放环境和排除笼中高。这些结果再次证明，高达〜40 mm SL的牡蛎很容易被捕食，影响这些牡蛎的至少某些死亡率可以归因于青蟹的捕食。鉴于这些双壳类提供的经济利益和生态系统服务，对小牡蛎的绿蟹捕食率是相关的。他们强调该行业需要考虑缓解措施并可能适应其牡蛎生长策略。