In Eilat, Israel's southernmost city bordering Egypt and Jordan, researcher Lisa-Maria Schmidt remembers when 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, a large number of sea urchins had died in a very short time.

The scientists, says Schmidt, go to a site known to be teeming with Diadema setosum, and they find only "skeletons and clusters of spines" of these sea urchins-diadems, a species characterized by its very long radiols and a clearly visible orange circle on a black body.

The idea came to them that a one-time chemical spill or pollution episode might have played a role in these deaths.

But in the two weeks that followed, the Diadema setosum they raised a little further down 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 the water of the Red Sea are extinguished.

A sea urchin Diadema setosum in an aquarium at the Inter-University Institute for Marine Sciences in the Israeli city of Eilat, on the Red Sea, September 14, 2023 © MENAHEM KAHANA / AFP

The scientists then ruled out the hypothesis of an exceptional accident and intensified their research to discover the cause of these sudden deaths.

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

"Scary"

According to Schmidt, Diadema setosum were the most common sea urchin species off Eilat, 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 corals, which need access to light to grow.

Omri Bronstein, a marine invertebrate specialist at Tel Aviv University, examines a jar containing Echinothrix sea urchins at a repository at the Steinhardt Museum of Natural History in Tel Aviv, August 21, 2023 © JACK GUEZ / AFP

Algae "grow more easily than corals, they suffocate them and thus kill entire expanses of reefs," she explains.

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

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

Researcher Lisa-Maria Schmidt (R) and a student at Tel Aviv University observe a sea urchin in an aquarium at the Inter-University Institute for Marine Sciences in Eilat, southern Israel, September 14, 2023 © MENAHEM KAHANA / AFP

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

Guesses

But Caribbean coral reefs never recovered from the mass death of local sea urchin populations in the 1980s.

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

Fish swim near a coral reef in Red Sea waters near the Israeli city of Eilat, September 14, 2023 © MENAHEM KAHANA / AFP

"The coral reefs of the West Indies have completely changed: (we have gone from) an environment where corals dominate (as in the Red Sea) to an environment where algae prevail," Omri Bronstein, a marine invertebrate specialist at Tel Aviv University, told AFP.

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

"Is this the same pathogen [if that's the cause] that hit the West Indies" forty years ago, "or are we facing a completely different scenario?"

One thing seems certain, according to him: stopping the contagion is impossible because "we cannot treat the ocean as we have treated humans with Covid", through vaccines.

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

A sea urchin Diadema setosum in an aquarium at the Inter-University Institute for Marine Sciences in the Israeli city of Eilat, on the Red Sea, September 14, 2023 © MENAHEM KAHANA / AFP

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

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

© 2023 AFP