PREVIEW

Last year, scientists discovered that the Red Sea was suffering a silent epidemic.
A deadly pathogen had infected the region’s sea urchins, which are considered key species essential for the functioning of coral reefs.
Normally, sea urchins act as coral reef gardeners – feeding on the algae which compete with coral for sunshine and might otherwise take over and suffocate reef life.
But just off the shore of Eilat, in occupied Palestine, a deadly pathogen has effectively wiped out the most locally abundant and ecologically significant sea urchin species.
Not only could this mass mortality threaten the Eilat reef, but it could also serve as a ‘patient zero’ for the pathogen’s spread across the Red Sea and into the Indian Ocean, scientists warned.
Researchers at Tel Aviv University announced last month that, during their continuing study on the reef, they had identified the pathogen and determined that it threatened entire populations of sea urchins across the Indo-Pacific and may become a global pandemic.
They found that the epidemic began in December 2022, and has since annihilated most sea urchin populations in the Red Sea and killed hundreds of thousands worldwide.
Since the epidemic’s discovery, the two species of sea urchin previously dominant in the Red Sea have been completely eradicated.
The culprit: a scuticociliate parasite most similar to Philaster apodigitiformis.
“This is a growing ecological crisis, threatening the stability of coral reefs on an unprecedented scale. Apparently, the mass mortality we identified in Eilat back in 2023 has spread along the Red Sea and beyond - to Oman, and even as far as Reunion Island in the Indian Ocean,” study lead Dr. Omri Bronstein said in a statement. “In our study we also demonstrated that the epidemic is spreading along routes of human transportation in the Red Sea. The best example is the wharf in Nueiba in Sinai, where the ferry from the Jordanian city of Aqaba docks.”
He added, “When we published our report last year, we already knew of sea urchin mortalities in Aqaba, but had not yet identified signs of it in Sinai. The first spot in which we ultimately did identify mortality in Sinai was next to this wharf in Nueiba.
“Two weeks later the epidemic had already reached Dahab, about 70km further south. The scene underwater is almost surreal: seeing a species that was so dominant in a certain environment simply erased in a matter of days.”
The pathogen is carried by water and can infect multiple sea urchin species.
The infection is quick and violent, according to the Tel Aviv University scientists.
Within two days of infection, a healthy sea urchin turns into a bare skeleton with no tissues or spines.
Most infected sea urchins are killed by predators before dying from disease, unable to defend themselves.
There is currently no cure or vaccination for sea urchins against the pathogen.
“Thousands of skeletons rolling on the sea bottom, crumbling and vanishing in a very short time, so that even evidence for what has occurred is hard to find,” Dr. Bronstein described. “Unfortunately, we cannot repair nature, but we can certainly change our own behavior. First of all, we must understand what caused this outbreak at this time.”
He continued, “Is the pathogen transported unknowingly by seacraft? Or has it always been here, erupting now due to a change in environmental conditions?
“These are precisely the questions we are working on now.”
This unicellular organism was responsible for the mass mortality of the Diadema setosum sea urchins in the Red Sea since December 2022 – but this was not its first kill.
Two years ago, the same pathogen was associated with the mass mortality of Diadema antillarum sea urchins in the Caribbean, following a 1983 sea urchin population collapse in the area which led to catastrophe in the surrounding reef.
Without sea urchins to manage the algae population, the reef turned into an algae field – suffocating the coral below.
Even though the Caribbean reef collapsed over 40 years ago, scientists have tracked repeated mortality events over the years because the ecosystem was unable to fully recover.
The Tel Aviv University researchers recommended establishing broodstock populations of endangered sea urchin species, so they can be reintroduced to the sea in the future.