Red Sea coral study points to rich microbial life as key to healthy reefs

In a discovery that could help rehabilitate reefs damaged by global warming, pollution and overfishing worldwide, Israeli and Australian researchers have discovered that rich and diverse communities of bacteria and invertebrates help corals to thrive.

The findings echo the results of growing terrestrial research showing how important microscopic creatures such as bacteria and fungi are to the health of soil and plants.

The research team designed terracotta tiles to replicate the complex 3D structure of natural coral reefs. They placed some tiles on a healthy reef and others on a damaged one in the Gulf of Eilat, on Israel’s southern tip.

During six months underwater, the tiles were colonized by diverse reef invertebrates and bacteria. Then, they were swapped around. Tiles from the healthy reef were taken to the damaged one, and vice versa.

Two species of corals were attached to the tiles and left for another six months, after which the microbial life on all the tiles was tested.

The researchers found that life was richer and more diverse on the tiles moved from the healthy reef to the damaged one.

Corals form symbiotic relationships with algae, in which the former provides a home and the latter makes food through photosynthesis.

Tiles like these, showing corals growing on a healthy community of bacteria and invertebrates, were used in the research off the coast of Eilat in southern Israel. (Meron Segev)

Corals formed on the tiles with the livelier communities of bacteria and invertebrates performed better in these symbiotic relationships, with a greater ability to photosynthesize, and were less stressed.

“This innovative approach underscores the critical role of healthy reef ecosystems in restoring coral health and resilience,” said Bar-Ilan University’s Natalie Levy, who led the research. “The results highlight the potential of ecosystem transplantation as an effective, sustainable restoration tool that can be integrated with other coral restoration methods like coral gardening and artificial reefs,” she said.

Prof. Oren Levy, also of Bar-Ilan University, added that the research “advances our understanding of coral restoration and provides an invaluable tool to help address the ongoing global coral crisis. By using healthy ecosystems to regenerate damaged reefs, we can work towards more resilient, sustainable coral ecosystems that may one day recover from climate change and other threats.”

The researchers, who also included Prof. Ezri Tarazi of the Technion – Israel Institute of Technology in the northern city of Haifa and Prof. David Bourne of James Cook University and the Australian Institute of Marine Science, published their findings this month in the journal Nature Communications.

Fish and coral in the Red Sea, near the southern city of Eilat. (Prof. Maoz Fine)

While they cover less than a percent of the ocean floor, coral reefs are home to more than a quarter of marine life.

However, due to climate change, overfishing, and pollution, more than half the world’s reefs have been lost since the 1950s.

The coral reefs of the Gulf of Eilat in southern Israel were expected to continue thriving in warmer waters for some time, for evolutionary reasons. According to coral expert Prof. Maoz Fine of the Interuniversity Institute for Marine Sciences in Eilat and Jerusalem’s Hebrew University, Eilat’s corals spent 6,000 years moving from the Indian Ocean through the Bab el-Mandeb strait between Djibouti and Yemen. Only those able to bear the hot water there could pass through and move into the northern Red Sea and the Gulf of Eilat.

An undated picture showing a coral that underwent bleaching in the Gulf of Eilat earlier this year. (Omri Omessi/ Assaf Zvuloni, Israel Nature and Parks Authority)

That theory was thrown into question earlier this month with the first reports of coral bleaching off Eilat’s coast.

According to experts, including Fine, who wrote in the Israeli academic journal “Ecology and Environment,” this follows an unprecedented rise in seawater temperature.

When water temperatures rise above a critical threshold, the corals expel the algae, and their white skeletons become visible, hence the term “bleaching.” Unless conditions revert rapidly, the corals eventually starve to death.