DEEPLIFE in Marine Environmental Research (2023)

Reef-building corals co-exist with antipatharians, commonly known as black corals. Antipatharians are particularly abundant at mesophotic depths, where they can form dense aggregations called Marine Animal Forests. These habitats act as spawning, nursery and feeding areas that support diverse animal communities, and create biodiversity hotspots.

Understanding the capacity of mesophotic corals to cope with heat stress is important to predict how climate change will shape the future of the reefs, from shallow to mesophotic areas.

The collaboration between UNDER THE POLE, the Université Libre de Bruxelles, and the French National Centre for Scientific Research (CNRS) allowed to assess for the first time the thermal sensitivity of corals from lower mesophotic zone at 85 m depth (45m at the deepest in previous studies). Coral sensitivity to global warming was compared to the ones of shallower corals at 25m depth.

Sampling of corals (Reef-building corals: Pachyseris speciosa, black corals: Stichopathes sp.) was carried out in Mo’orea (French Polynesia) at 25m and 85 m depth by technical divers from UNDER THE POLE. Corals were installed in 200 L-aquaria to be exposed to different temperature treatments (23°C to 32°C) for 10 days. Thermal performances and metabolic responses of corals were determined to assess their capacity to cope with heat stress.

We revealed that mesophotic reef-building corals have a higher capacity to encompass large range of temperatures compared to their congeners at 25 m depth. It is likely because mesophotic colonies are exposed to more variable seawater temperatures created by the rise of deep cold and nutrientrich waters being uplifted up the reef slope (called internal waves). In Mo’orea, temperature variability increases with depth, with a temperature range of 4.6 °C at 90 m vs 2.9 °C at 20 m.

The present study also shows that black corals have lower thermal window of performance compared to reef-building corals in response to heat stress. It confirms our previous results revealing that black corals have poor thermal acclimatization capacity. Global warming could have significant consequences for this ecosystem-engineer species (see our publication by Godefroid et al., 2022).

Summary from the article "Thermal performance with depth: Comparison of a mesophotic scleractinian and an antipatharian species subjected to internal waves in Mo'orea, French Polynesia."

Read the full article via the link below.

Authors - Godefroid M., Dubois P., Under The Pole Consortium, Hédouin L.