The killer within: Endogenous bacteria accelerate oyster mortality during sustained anoxia

Sustained periods of anoxia, driven by eutrophication, threaten coastal marine systems and can lead to mass mortalities even resilient animals such as bivalves. While mortality rates under anoxia are well-studied, the specific mechanism(s) less clear. We used a suite complementary techniques (LT50, histology, 16S rRNA amplicon sequencing, valvometry) show that proliferation anaerobic bacteria within eastern oysters (Crassostrea virginica) accelerates rate anoxic conditions. Manipulative laboratory experiments revealed oyster survival conditions was halved when were present compared they excluded broad-spectrum antibiotic chloramphenicol. Histological assessments supported this mechanism showed infiltration in not treated with antibiotics general lack antibiotics. sequencing failed identify any particular genera responsible for mortality, rather diversity endogenous and/or sulfate-reducing common among oysters. In addition, monitoring valve gaping behavior field remarkable closure synchrony first exposed anoxia. However, periodically opened throughout anoxia/hypoxia both lab field, suggesting exogenous from environment may also influence natural settings. Coupled previous studies, we posit events wide range bivalves likely result co-morbidity asphyxiation bacterial processes.