Red Sea corals threatened by mysterious sea urchin slaughter

Scientists are concerned about the Red Sea's famous coral reefs after discovering that a mysterious illness is decimating a population of sea urchins essential to their survival

Red Sea corals threatened by mysterious sea urchin slaughter

Scientists are concerned about the Red Sea's famous coral reefs after discovering that a mysterious illness is decimating a population of sea urchins essential to their survival.

In Eilat, Israel's southernmost city, bordering Egypt and Jordan, researcher Lisa-Maria Schmidt remembers the moment she and her colleagues at Tel Aviv University discovered the scourge.

The investigation began in January when they learned that off the coast of Eilat, many sea urchins had died in a very short time.

The scientists, says Ms. Schmidt, went to a site known to be teeming with Diadema setosum, and there they found only "skeletons and piles of spines" of these diadem sea urchins, a species characterized by its very long radioles and a clearly visible orange circle on a black body.

The idea then came to them that a one-off spill of chemicals or an episode of pollution could have played a role in these deaths.

But in the two weeks that followed, the Diadema setosum that they raised a little further on the coast at the Inter-University Institute for Marine Sciences were affected in turn. In less than 48 hours, all these sea urchins installed in tanks fed by water from the Red Sea died out.

Scientists then exclude the hypothesis of an exceptional accident and intensify their research to discover the cause of these sudden deaths.

They realize that another species of sea urchin (Echinothrix calamaris) is also the victim of massive mortality in the same waters, but that apart from these two varieties, other populations continue to flourish in the middle of corals.

Diadema setosum were the most common sea urchin species off the coast of Eilat, Schmidt said, and their disappearance could have a devastating effect on the environment because these marine animals feed on rapidly growing algae.

By consuming them, they prevent them from covering the corals, which need access to light to grow.

Algae “grow more easily than corals, they suffocate them and thus kill entire areas of reefs,” she explains.

The massive mortality of sea urchins is something "particularly frightening" for the Red Sea where the corals "are known to be robust, and I think people have placed a lot of hope in these reefs", alarms Mya Breitbart, biologist at the University of South Florida, United States.

If they extend beneath only 0.2% of the sea surface, coral reefs would be home to more than 25% of the world's marine biodiversity.

Ms. Breitbart recently unraveled the mystery of a massive sea urchin mortality phenomenon in the West Indies by identifying a pathogen that in 2022 decimated entire colonies of a variety of sea urchins related to Diadema setosum.

But the West Indian coral reefs have never recovered from the massive death of local sea urchin populations in the 1980s.

If the cause of this evil is still not clearly identified to this day, the consequences are however well known.

“The coral reefs of the Antilles have completely changed: (we have gone) from an environment where corals dominate (like in the Red Sea) to an environment where algae prevail,” Omri Bronstein, a specialist in marine invertebrates, explains to AFP. at Tel Aviv University.

But when it comes to the Red Sea, Mr. Bronstein, who heads the researchers investigating in Eilat, is lost in conjecture.

“Is this the same pathogen [if that is the cause], as the one that hit the West Indies” around forty years ago, “or are we facing a completely different scenario?”

One thing seems certain, according to him: putting an end to the contagion is impossible because “we cannot treat the ocean like we treated humans with Covid”, through vaccines.

The scientist has another solution in mind: breed sea urchins of the two endangered species, keep them in captivity before releasing them into the Red Sea to repopulate the reefs when the danger has passed.

Once they have found the origin of these disappearances, Mr. Bronstein and his colleagues want to determine how the Red Sea could have been affected.

If pathogens have arrived by sea, measures could be taken to clean boats and minimize the risk of spread, because, surely, if one is faced with one deadly parasite, then the next one is already " en route", somewhere in a port or on a ship.

24/09/2023 17:00:29 -         Eilat (Israël) (AFP) -         © 2023 AFP