A Black Coral’s Survival Story
Date of publication: Nov 21, 2023

Based on: Gouveia, A., Godefroid, M., Dubois, P., Espino, F., Tuya, F., Haroun, R., Herrera, A. and Otero-Ferrer, F., 2023. Thermal stress response of Antipathella wollastoni (Gray, 1857) from the Canary Islands archipelago. Coral Reefs, pp.1-7.

In the cool, shadowy depths of Macaronesian waters, the black coral Antipathella wollastoni faces a crucial test—the rising temperatures of the ocean. Researchers, investigating how it will cope with this challenge, found that this species is quite the survivor, and possesses a very interesting survival adaptation.

Antipatharians, commonly known as black corals, are sessile colonial hexacorals that form extensive marine animal forests in various oceanic regions. These unique ecosystems play a crucial role in shaping local biodiversity. However, the vulnerability of black corals to environmental changes, particularly rising ocean temperatures, poses a significant concern for their conservation, and remains largely understudied. The study at hand focuses on Antipathella wollastoni, a black coral species found in the Macaronesian islands, aiming to assess its thermal tolerance and response strategies in the face of increasing temperatures.

Antipathella wollastoni marine forest in Lanzarote, at 65 m deep. Photo by F. Espino. 

Fragments of this coral were exposed to temperatures ranging from 19 to 26.5 °C, simulating the warming trends observed in the world’s oceans. The goal: to understand how this species responds to temperature variations.

The coral withstood the temperature increase with no fatalities. And its antioxidant capacity remained unaffected. Respiration rates, used to measure metabolic activity, followed a predictable pattern, peaking at the optimal temperature of 25.9 °C.

Adriana Gouveia performing anti-oxidant measurements in black coral colonies. Photo by F. Espino.

However, something else happened. As temperatures climbed, coral tissue narcosis increased, and the coral initiated a survival strategy—bailout propagules. These are small structures that detach from the mother structure and serve as a means of escape. Bailout propagules have been observed in other coral species to adapt to stressful conditions. This indicates that the A. wollastoni might have been stressed during the experiment. But, as mentioned by the authors, there are signs that this stress might have been induced by other experimental conditions besides increasing temperatures. For one, the corals produced propagules even within the temperature range they are usually subjected to in the wild. Propagules might have been created due to an elevated rate of temperature increase, or because the time it took to sample them. To figure that out, we must now wait for future studies.

Nevertheless, we now know something important, A. wollastoni possesses a degree of thermal tolerance that is valuable in the face of environmental changes.

Written by Maria Pinto