An epidemic that has decimated large numbers of sea urchins in the Gulf of Eilat has spread to the Red Sea and spilled over into the Indian Ocean. ‘This is an ecological disaster of the first order,’ say researchers at Tel Aviv University, recommending that urgent action be taken

Zafrir Rinat. May 23, 2024

A lethal epidemic that decimated the population of sea urchins in the Gulf of Eilat last year has spread along the entire length of the Red Sea and spilled over into the Indian Ocean, according to a study led by researchers at Tel Aviv University. 

The mass death of sea urchins poses a big threat for coral reefs, where sea urchins play a major role in maintaining normal reef functioning. Researchers still don’t know what led to the initial spread of the disease.

Current estimates are that since December 2022, when the epidemic first emerged in the Gulf of Eilat, most sea urchins that have been exposed to it in the Red Sea have died, and hundreds of thousands have died worldwide, although the exact numbers are unknown.

Researchers from Tel Aviv University have been following the condition of sea urchins over the last year, and have published their results in biweekly scientific journal Current Biology. 

Sea urchins have been described as the “gardeners” of coral reefs. They feed on algae, which compete with the corals for sunlight. Thus, their decimation could have serious adverse effects on coral reefs around the world. 

The researchers note that since the epidemic became known in the reef at Eilat, two major species of sea urchins have almost completely disappeared. The deaths were swift. Within two days, a healthy sea urchin becomes a skeleton with no tissue, lacking the ability to defend itself.

Dr. Omri Bronstein from TAU’s School of Zoology and the university’s Steinhardt Museum of Natural History lead the research, and he was assisted by research students Lachan Roth, Gal Eviatar, Lisa Schmidt and Mai Bonomo. An international team of scientists from Europe and Mideast countries, who followed the condition of sea urchins along thousands of kilometers of coral reefs, also participated in the study. 

The researchers from TAU used molecular-genetic tools to identify the pathogen responsible for the mass deaths of one species of sea urchin – a unicellular parasite which was responsible for the mass deaths of sea urchins in the Caribbean two years ago, leading to the collapse of coral reefs in that area. 

During the prolonged monitoring that began with the onset of the epidemic, it turned out that the pathogen had affected other species of sea urchins and had spread to additional areas. “This is an ecological disaster of the first order, threatening sea urchins all over the world,” says Bronstein. “It turns out that the widespread deaths we identified in Eilat have spread along the Red Sea and beyond. It has reached Oman, and is now ravaging Reunion Island in the Indian Ocean.”

The lethal parasite is carried in the water and can infect wide areas in a short period of time. Even sea urchins raised in seawater tanks or the underwater observatory at the Inter-University Institute for Marine Sciences in Eilat have been infected and died, since the pathogen can enter through pumping facilities. The institute’s research team documented for the first time all the stages of the disease, from infection to death. 

Until recently, researchers knew of only one species of sea urchins – Diadema Antilarum – to be infected by the disease in the Caribbean Sea. Researchers had hoped that nature would find a way of compensating for the harm caused to one species, for instance by an increase of populations of other sea urchin species, but the study conducted in Israel shows that closely-related species, such as the one in the Red Sea, as well as other species in the same family, are exposed to the disease. 

Estimates are that the parasite spread, among other ways, with the help of vessels, since there was a correlation between the manner in which it spread across the Red Sea and marine traffic in the area. 

“We showed that the epidemic spreads along maritime routes used by humans. The best example was in the town of Nuweiba, on the Sinai coast,” says Bronstein. “There is a little wharf there for ferries going between Nuweiba and Aqaba, in Jordan. The first location in which sea urchins started dying in Sinai was close to the small port in Nuweiba, where ferries from Aqaba dock. Two weeks later, the epidemic had spread as far as Dahab, 70 kilometers (43.5 miles) away. The underwater scene is almost surreal: thousands of sea urchin skeletons are rolling in the sea bed, crumbling and vanishing in a very short time, making it difficult to find evidence of what took place.” 

There is currently no way of helping infected sea urchins or of immunizing them. According to the researchers, reproduction nuclei must quickly be established for at-risk species. These must be kept in growth facilities that are completely dissociated from the sea, so that in the future, sea urchin populations impacted by the disease can be restored. 

“Regrettably, we have no way of repairing nature,” notes Bronstein. “But we can fix what we do. Primarily, we must understand what caused the outbreak at the present time – whether this was an unintentional transmission of a pathogen by passing vessels, or whether the pathogen has always been around, with changes in the environment causing it to suddenly spread. We are currently trying to find answers to these questions.”