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

by Jacqueline Alva Garcia, Shannon G. Klein, Taiba Alamoudi, Silvia Arossa, Anieka J. Parry, Alexandra Steckbauer, Carlos. M. Duarte
original article Year: 2022 DOI:


Alva García, J.V. ,  S.G. Klein, T. Alamoudi, S. Arossa, A.J. Parry, A. Steckbauer, and C.M. Duarte. 2022. Thresholds of Hypoxia of Two Red Sea Coral Species (Porites sp. and Galaxea fascicularis). Frontiers in Marine Science 9:945293. doi: 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.