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

Abstract

Climate change is accelerating the deoxygenation of aquatic ecosystems, so understanding its effects on biological processes is increasingly critical. An emerging method for inducing hypoxia during experimentation utilizes sodium sulfite (SSI) to scavenge oxygen; however, it remains unclear if hypoxia-inducing concentrations of SSI are toxic to aquatic species. We decoupled SSI's potential toxicity from its hypoxia-inducing effects by rapidly replacing the oxygen it removes via vigorous aeration. We examined the model species Exaiptasia diaphana (a sea anemone) and its endosymbiotic dinoflagellates by exposing them to a dosage that mimics the diel oxygen cycle for 2 weeks. We examined common stress indicators, including the anemone's metabolic rates and thermal tolerance, the algae's photosynthetic efficiency, cell density, and reproduction in treated and untreated specimens, finding no effects of SSI exposure. A second trial assessed acute toxicity, finding that anemones lacked observable stress responses after 21.2 times the concentration needed to induce anoxia. We therefore conclude that SSI is a viable, cost-effective, and nontoxic way to induce hypoxia in this species and that this method shows broad potential for hypoxia studies on other aquatic organisms.