NCCOS-supported researchers investigating the effects of hypoxia (low oxygen) on threatened coral species discovered that some species have surprisingly high tolerance to declining ocean oxygen levels. While investigating staghorn coral (Acropora cervicornis) and mountainous star coral (Orbicella faveolata), researchers found the hypoxia tolerance of both species to differ significantly.

Acropora cervicornis was more sensitive to low oxygen and suffered tissue loss (in box at base of coral nubbin) and mortality within days of exposure to the most hypoxic treatment, while Orbicella faveolata showed no visible signs of treatment effects after two weeks of exposure. Credit: Johnson et al. (2021).

Exposure of coral fragments showed staghorn coral to be more sensitive to severe hypoxia (~1 mg/L) with signs of tissue loss within five days, whereas the mountainous star coral demonstrated no visible effects from severe hypoxia after two weeks of exposure.

Tropical coral ecosystems experience hypoxia naturally, sometimes daily. Although some tropical organisms, including some corals, appear well adapted to living in hypoxic conditions, there is concern regarding how other stressors (such as increasing ocean temperatures, ocean acidification, and eutrophication) may increase the effects of hypoxia. “Our goal is to understand how hypoxia affects coral species used in restoration and support the unprecedented coral restoration efforts happening throughout Florida’s Coral Reef, including NOAA’s Mission: Iconic Reefs program,” said project PI Andrew Altieri.

This project is part of the NCCOS Coastal Hypoxia Research Program (CHRP), and is led by the University of Florida in collaboration with the Smithsonian Institution. It is examining the impact of hypoxia on coral reef ecosystems.

Citation: Johnson, Maggie D., Sara D. Swaminathan, Emily N. Nixon, Valerie J. Paul and Andrew H. Altieri. 2021. Differential susceptibility of reef-building corals to deoxygenation reveals remarkable hypoxia tolerance. Scientific Reports 11: 23168. https://doi.org/10.1038/s41598-021-01078-9