Scientists are worried about the Red Sea’s famed coral reefs after discovering a mysterious disease is decimating a vital population of sea urchins.
In Eilat, Israel’s southernmost city on the border with 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 it was learned that many sea urchins had died in a very short time off the coast of Eilat.
The scientists, says Ms. Schmidt, went to a place 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 very long radioles and a clearly visible shape is distinguished by an orange circle on a black body.
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Then they came up with the idea that a one-time chemical spill or environmental pollution might have played a role in these deaths.
But in the following two weeks, Diadema setosum, which they bred a little further on the coast at the Interuniversity Institute of Marine Sciences, was again affected. In less than 48 hours, all the sea urchins housed in tanks fed with water from the Red Sea died out.
Scientists then rule out the hypothesis of a freak accident and intensify their research to find out the cause of these sudden deaths.
They find that another sea urchin species (Echinothrix camaris) is also the victim of a massive die-off in the same waters, but that other populations besides these two species continue to thrive among corals.
Omri Bronstein of Tel Aviv University examines a jar of Echinothrix calamari sea urchins in the storage rooms of the Steinhardt Museum of Natural History in the Israeli Mediterranean coastal city of Tel Aviv on August 21, 2023. (Source: JACK GUEZ / AFP)
Diadema setosum is the most common sea urchin species off the coast of Eilat, Schmidt said, and its disappearance could have devastating effects on the environment because these sea creatures feed on fast-growing algae. By consuming them, they prevent them from covering the corals, which need access to light to grow.
Algae “grows more easily than corals, suffocating them and killing entire reefs,” she explains.
The massive die-off of sea urchins is “particularly frightening” for the Red Sea, where the corals are “known to be resilient, and I think people have placed great hope in these reefs,” warns Mya Breitbart, a biologist at the University of South Florida, United States States.
If they covered less than 0.2% of the ocean’s surface, coral reefs would be home to more than 25% of the world’s marine biodiversity.
Gal Eviatar, a student at Tel Aviv University, holds a Diadema setosum sea urchin with tweezers in an aquarium at the Interuniversity Institute of Marine Sciences in the Israeli Red Sea resort of Eilat on September 14, 2023. (Source: MENAHEM KAHANA / AFP)
Ms. Breitbart recently unraveled the mystery of a massive sea urchin mortality phenomenon in the Antilles by identifying a pathogen that decimated entire colonies of a sea urchin species related to Diadema setosum in 2022.
But West Indian coral reefs have never recovered from the massive die-off of local sea urchin populations in the 1980s.
Even if the cause of this evil is not yet clearly understood, the consequences are well known.
“The coral reefs of the Antilles have completely changed: (we are) from an environment where corals dominate (like in the Red Sea) to an environment where algae predominate,” Omri Bronstein, a marine invertebrate specialist, tells AFP . at Tel Aviv University.
But when it comes to the Red Sea, Mr. Bronstein, who leads the researchers investigating in Eilat, gets lost in guesswork.
“Is it the same pathogen? [si telle est la cause], than that which struck the West Indies some forty years ago, or are we facing a completely different scenario? »
According to him, one thing seems certain: it is impossible to put an end to the contagion because “we cannot treat the ocean the way we treated people with Covid,” through vaccines.
The scientist has another solution in mind: He will breed sea urchins of the two endangered species, keep them in captivity, and then release them into the Red Sea to repopulate the reefs when the danger has passed.
A staghorn coral releases eggs and sperm that are carried by the current. (Image credit: Tom Shlesinger)
Once they find the origin of these disappearances, Mr. Bronstein and his colleagues want to find out how the Red Sea might have been affected.
If pathogens have arrived via the sea, measures could be taken to clean boats and minimize the risk of spread, because if we are dealing with one deadly parasite, then the next one is probably already “on the way”, somewhere in you Port or… on a ship.