Thresholds of hypoxia of two Red Sea coral species (Porites sp. and Galaxea fascicularis)

• Published in: Frontiers in Marine Science
• Main Authors: Alva García, Jacqueline V., Klein, Shannon, Alamoudi, Taiba, Arossa, Silvia, Parry, Anieka J., Steckbauer, Alexandra, Duarte, Carlos M.
• Other Authors: Red Sea Research Center (RSRC), Biological and Environmental Science and Engineering (BESE) Division, Marine Science Program, Computational Bioscience Research Center (CBRC)
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2022
• Subjects: Prieto; Ocean acidification
• Online Access: http://hdl.handle.net/10754/685949; https://doi.org/10.3389/fmars.2022.945293

Anthropogenic pressures have driven large-scale declines in coral cover on >50% of tropical coral reefs. Most research efforts have focused on ocean warming, ocean acidification, and overfishing impacts. Despite increasing instances of reef-associated hypoxic events, the role of reduced O2 in affecting coral reef performance is largely unknown. Here, we assessed the hypoxic thresholds of two Red Sea coral species: Porites sp. and Galaxea fascicularis. We exposed coral fragments of both species to one control treatment (6.8 mg O2 L−1) and three reduced dissolved oxygen treatments (5.25, 3.5, and 1.25 mg O2 L−1) during a 10-day experiment. Across the two species, maximum (Fv/Fm) and effective (F′/Fm′) photochemical efficiency, chlorophyll a, and dark respiration declined under the lowest O2 treatment (1.25 mg O2 L−1). Porites sp. coral fragments, however, were remarkably resistant and showed no signs of sublethal bleaching after 10 days of exposure to reduced O2. Conversely, 17% of G. fascicularis fragments bleached after only three nights of exposure to the lowest O2 treatment (1.25 mg O2 L−1). Our data show that longer-term hypoxic events (i.e., days to weeks) can induce coral bleaching, but these effects depend on the extent of O2 reduction and are likely species-specific. Importantly, the levels of O2 usually defined as hypoxic (~2.0 to 2.8 mg O2 L−1) do not adequately capture the thresholds reported here. Hence, further research is urgently needed to more accurately describe the vulnerability of coral taxa to hypoxic and anoxic events. Funding supporting this research was provided by the King Abdullah University of Science and Technology through baseline research funds awarded to CD. We thank S. Schmidt-Roach and A. Prieto for their help with the collection and maintenance of the corals. We also thank the KAUST Coastal and Marine Resources Core Labs (CMR) team for their support and assistance.