A new study conducted by Tel Aviv University shows that corals in deeper water are reproducing less than their shallow-water peers.
Researchers at Tel Aviv University, in collaboration with the Interuniversity Institute for Marine Sciences in Eilat, found that coral spawning events in the Gulf of Aqaba in the Red Sea, at the deeper parts of the reef (30-45 meters) occur at significantly lower intensities than those at shallower depths (0-30 meter).
In shallow water, around half of the corals engaged in each reproductive event, however, it declined significantly in deeper water, the study showed.
“Whereas at a shallow depth, about half of the colonies participated in each spawning event, in the deeper water the participation rate dropped to only 10–20%,” Ronen Liberman, head-researcher and Ph.D. candidate at Tel Aviv University’s School of Zoology, was quoted as saying in a press release.
In the study, the researchers focused on a soft coral, named rhytisma fulvum, that reproduces by “surface-brooding” — a reproductive method by which the coral brood, or hatch, their strikingly yellow larvae glued externally to the coral surface for several days.
The new findings contradict the popular belief that deep reefs can serve as a “lifeline” for degraded shallow reefs. In fact, this study concludes that the opposite may be the case.
Deep corals are to a certain degree dependent on populations from the shallower reef as the corals in the deep reefs are not exposed to as much sunlight as the colonies in the shallower waters, the researchers suggested.
Sunlight is crucial for photosynthesis in which symbiotic algae found within the coral tissue convert light energy to provide the coral host with the chemical energy it needs, the study concluded.
“Today, when coral reefs around the world are being severely damaged by climate change and other human impacts, many are pinning their hopes on deeper reefs to provide a lifeline of support for shallow-water coral reefs, which may be more exposed to some hazards,” Liberman said, explaining that this hope for the deep corals might have been "overestimated."
"Therefore, these hidden deep reefs require attention and protection on their own right, perhaps even more than shallow reefs,” he added.