Unveiling the impact of warming and high salinity on winter mass mortality in oysters

Oysters profoundly contribute to both aquaculture and ecological systems. Nonetheless repeated mass mortality events are prevalent in crucial oyster aquaculture species, a situation that is intensifying due to environmental changes. Existing research on oyster mortality primarily focuses on field observations or the validation of single predisposing factor. It is unclear, however, the phenotypic and molecular mechanisms underlying oyster mortality triggered by the interaction between multiple biotic and abiotic stressors. This research used in-lab experiments simulating high salinity and temperature environments in reference to the actual natural conditions in winter season to investigate the survival, energy-related metabolite contents, gene expression and bacterial community variations in oysters under the two environmental stressors alone and combined. Furthermore, Vibrio aestuarianus was injected into those stressed oysters. The survival data demonstrated a robust synergistic effect of high salinity and temperature, which was supported by gene expression profiles and energy metabolite content. Long-term exposure to environmental stressors altered gene expression patterns and disrupted energy metabolic balance. The Vibrio infection together with single environmental stressor did not trigger rapid mass mortality of oysters, although it modified the community structure of the hemolymph-associated bacteria. This study showed single environmental stressor is unlikely to cause oyster mortality, whereas combined effect of two stressors resulted in rapid mass mortality. Despite the need for further studies to identify the full spectrum of causes of winter mortality, this study holds substantial implications for sustainable aquaculture management amidst global changes.