Sodium sulfite can reliably induce chemical hypoxia without toxic effects in the model sea anemone species, Exaiptasia diaphana

Climate change is accelerating deoxygenation in aquatic ecosystems worldwide, causing consequences for aerobic organisms. Empirically studying the effects of deoxygenation on biological processes is therefore critical. Multiple methods for inducing hypoxia in physiological studies have been developed, each with pros and cons. Using oxygen scavenger chemicals, such as sodium sulfite, to reliably and inexpensively induce hypoxia in aquatic systems is gaining popularity, however its potential toxicity remains unknown and studies decoupling exposure to the salt from its hypoxic effects are lacking. To address this, we investigated the effects of sodium sulfite and the product of its oxidation, sodium sulfate, on the model sea anemone, Exaiptasia diaphana and its endosymbiotic dinoflagellates. To separate the effects of the salt itself and hypoxia, we provided vigorous aeration which quickly replaced sodium sulfite scavenged oxygen. In the first experiment, we exposed anemones to a hypoxia-inducing dosage of sodium sulfite (0.125 g/L), the equivalent concentration of sodium sulfate or a seawater control for two weeks under vigorous aeration to prevent actual hypoxia. Then, we measured the anemone’s metabolic rates and their thermal tolerance. We also measured the algae’s photosynthetic efficiency, cell density and reproduction. Neither sodium sulfite nor sodium sulfate exposure affected any of these parameters, allowing us to conclude that exposure to these salts at these concentrations is not toxic for E. diaphana. We then conducted a second experiment to determine how much sodium sulfite and sodium sulfate anemones could withstand before displaying behavioral signs of stress. After exposure to 70x (8.75 g/L), well beyond the concentration needed to induce anoxia when vigorous aeration is not provided, anemones showed no sign of stress, indicating that exposure to these salts at these concentrations is not acutely stressful. We therefore conclude that sodium sulfite is a viable and non-toxic way to scavenge oxygen and induce hypoxia in laboratory settings.