Two mass mortality events (MMEs) of marine mussels that took place in the Oosterschelde, the Netherlands—the first in 2015/2016 and the second in 2019—both severely affected mussel production. The current study presents our observations on the onset and course of both MMEs and discusses probable putative causes. The two MMEs displayed a distinct course of events. The first event started in November 2015 with high mortality rates on culture plots, which remained elevated until the autumn of 2016. Approximately 40–50% of mussels from all age classes were lost on culture plots and 100% were lost from wild seed beds. The second event started in April–May 2019 and continued until the end of July, with mortality ranging from 20 to 100%, again from all age classes. Culture areas other than the Oosterschelde and other shellfish species were not affected. Histological and bacteriological screening produced no evidence for common pathogens or pollution as a primary mortality factor and there is no indication of abnormal environmental conditions preceding or during the events. We hypothesize that a cumulation of stressors results in weakening of the mussels and in elevated mortality rates. In 2019, this cumulation of stressors could be high spawning activities (an unusual high concentration of mussel larvae was found in April) that resulted in very low condition from April to June, a Phaeocystis bloom in April to May that prevented a quick recovery, and the development of granulocytomas that were found in up to 60 to 70% of live mussels as a consequence of cumulative stress. Although no (single) putative causes could be identified, this study contributes to the knowledge on MMEs in mussels and fits in a wider and disturbing trend on mortality events in shellfish.

荷兰Oosterschelde发生了两次海洋贻贝的大规模死亡事件（MME），第一次是2015/2016年，第二次是2019年，这两个事件都严重影响了贻贝的生产。当前的研究提出了我们对两种MME的发病和病程的观察，并讨论了可能的推定原因。这两个MME显示出不同的事件过程。第一次事件始于2015年11月，耕地死亡率高，一直持续到2016年秋。在各个耕地中，约有40–50％的各个年龄段的贻贝在耕地上流失，而100％的野生苗床流失。第二次事件始于2019年4月至5月，一直持续到7月底，死亡率从20％到100％，再次出现在所有年龄段。除Oosterschelde和其他贝类以外的其他养殖地区均未受到影响。组织学和细菌学筛查没有发现常见病原体或污染作为主要死亡因素的证据，也没有迹象表明在事件发生之前或之中发生异常的环境状况。我们假设压力源的累积会导致贻贝变弱和死亡率上升。在2019年，这种压力源的累积可能是高产卵活动（4月发现了贻贝幼虫的异常高浓度），导致4月至6月的情况非常低，我们假设压力源的累积会导致贻贝变弱和死亡率上升。在2019年，这种压力源的累积可能是高产卵活动（4月发现了贻贝幼虫的异常高浓度），导致4月至6月的情况非常低，我们假设压力源的累积会导致贻贝变弱和死亡率上升。在2019年，这种压力源的累积可能是高产卵活动（4月发现了贻贝幼虫的异常高浓度），导致4月至6月的情况非常低，藻孢在4月至5月开花，阻止了其快速恢复，并且由于累积的压力，在多达60％至70％的活贻贝中发现了粒细胞瘤的发展。尽管没有发现（单个）可能的原因，但这项研究有助于了解贻贝中的MME，并且适合贝类死亡事件的更广泛且令人不安的趋势。