The combined effects of temperature and exogenous bacterial sources on mortality in the Eastern oyster (Crassostrea virginica) under anoxia.

Abstract

In aquatic environments, low dissolved oxygen concentrations can result in depressed bivalve defense systems while promoting anaerobic bacterial growth, ultimately leading to increased bivalve mortality rates. Although the relationship between low oxygen availability and bivalve mortality has been previously examined, the mechanisms of mortality remain not well understood, limiting our ability to predict mass mortality events. In this study, the effect of anoxia (< 0.1 mgO₂L^-1) on adult oyster (Crassostrea virginica) mortality rates was explored experimentally using a factorial design, which included the effect of temperature (20°C vs. 28°C) combined with the presence/absence of an exogenous bacterial source (anoxic sediment vs. sterile sediment). Additionally, the effect on oyster mortality rate of removing vs. not removing deceased oysters from the experimental chambers was assessed. Oyster mortality rates, estimated as the time taken for half of the population to die (LT₅₀) in anoxic conditions were significantly affected by temperature, the presence of anoxic sediment, and experimental execution (removing vs. not removing deceased oysters). Temperature had the greatest effect on mortality overall, with high temperatures resulting in increased mortality rates, whereas the presence of anoxic sediment only increased mortality rates consistently at high temperatures. The results of this study suggest that bacterial sources play a role in the mortality rate of oysters under warm anoxic conditions.

Supplementary information: The online version contains supplementary material available at 10.1007/s00227-025-04617-4.