New experimental results have shed more light on the ability of cold-water corals to live in low-oxygen conditions. The reef-forming cold-water coral Desmophyllum pertusum (formerly Lophelia pertusa) is found across a wide range of water depths (50–3000 m depth) in the Atlantic Ocean and further afield, usually thriving in food-rich, well-oxygenated waters under strong bottom currents. Although the coral is able to tolerate a range of oxygen levels, previous laboratory studies have shown that it is unable to maintain normal aerobic metabolic activity below approximately 3 mL L−1, suggesting that D. pertusum should not be found in low-oxygen environments.
However, recent expeditions discovered live D. pertusum reefs under hypoxic conditions along the Angolan margin in the southeastern Atlantic Ocean, where a low-oxygen zone exists as a result of high surface primary production in an upwelling zone. Despite these low oxygen conditions, the Angolan coral reefs have a dense living coral cover with a diverse associated fauna.
To better understand the physiological performance of D. pertusum in the hypoxic waters off Angola, iAtlantic scientists performed an experiment to assess coral respiration rates under naturally low oxygen concentrations and after short-term (7 days) exposure to increased oxygen conditions. The study – carried out on board RV Meteor during the ANNA cruise and now published as a peer-reviewed paper – aimed to explore the potentially limiting effect of low oxygen concentrations on coral metabolism. Hypoxia typically limits respiration, resulting in reduced metabolic rates, up to death. The team tested two experimental hypotheses: (1) D. pertusum respiration at naturally hypoxic conditions is limited by oxygen availability and will therefore increase under increased oxygen concentration; (2) D. pertusum respiration at naturally hypoxic conditions will be lower than previous records for the species at normoxic conditions.
Results show that, under controlled experimental conditions aboard RV Meteor, specimens of D. pertusum sampled from hypoxic waters along the Angola margin displayed the same respiration rates under naturally low oxygen as well as under increased oxygen concentrations. Furthermore, these respiration rates were in the same order of magnitude as those of the species living under normoxic conditions in other areas.
This work expands the current knowledge on the metabolic activity of cold-water corals under hypoxic conditions, providing evidence that low oxygen conditions are not a general limiting factor for the overall distribution of D. pertusum.
Read the full paper: Andrea Gori, Covadonga Orejas, Furu Mienis, Christine Ferrier-Pagès, Meri Bilan, Sebastian Flöter, Stephanie Reynaud, Andrew K. Sweetman, J Murray Roberts, Claudia Wienberg and Dierk Hebbeln (2023) Natural hypoxic conditions do not affect the respiration rates of the cold-water coral Desmophyllum pertusum (Lophelia pertusa) living in the Angola margin (Southeastern Atlantic Ocean). Deep Sea Research Part I. https://doi.org/10.1016/j.dsr.2023.104052