Israeli scientists have found the cause of a mass epidemic that wiped out all the sea urchins last year in the Red Sea. Just a year ago, the entire population of black sea urchins in Eilat was wiped out within weeks.
Sea urchins, usually abundant and ecologically significant, are considered the ‘gardeners’ of coral reefs, feeding on the algae that compete with the corals for sunshine – and their disappearance can severely impact the delicate balance on coral reefs worldwide. A deadly pathogen is wiping them out.
Deadly Epidemic Wipes Out Black Urchins in Gulf of Eilat, Threatens Coral Reef
The research study into the issue at Tel Aviv University encompassed thousands of kilometers of coral reefs in its quest to find the cause of the epidemic. The alarming results were published in the leading scientific journal Current Biology.
By using molecular-genetic tools, the research group at TAU identified the pathogen responsible for the mass mortality of sea urchins of the species Diadema setosum in the Red Sea.
Diadema setosum are the long-spined black sea urchins that were very common in the northern Gulf of Eilat, Jordan, and Sinai.
Their killer is a scuticociliate parasite most similar to Philaster apodigitiformis, a unicellular organism that was also responsible for the reoccurring mass mortality of Diadema antillarum in the Caribbean.
The researchers now warn that the pathogen they identified has caused a global pandemic that has spread not only across the Red Sea but also into the Indian Ocean Since the outbreak in December 2022, the epidemic has annihilated an estimated hundreds of thousands of sea urchins worldwide.
The researchers note that since the discovery of the epidemic in Eilat’s coral reefs, both species of sea urchins previously most dominant in the Gulf of Eilat have vanished completely.
The study was led by Dr. Omri Bronstein from the School of Zoology and the Steinhardt Museum of Natural History (SMNH), together with research students Lachan Roth, Gal Eviatar, Lisa Schmidt, and May Bonomo, as well as Dr. Tamar Feldstein-Farkash from the SMNH. Research partners throughout the region and Europe also took part.
Bronstein and his team have also found that the epidemic was lethal for other, closely related sea urchins from the genus Echinothrix as well.
The results suggest the once most abundant and significant seabed herbivores in the region are now practically gone and are disappearing elsewhere.
Thousands of sea urchins died a quick and violent death – within two days a healthy sea urchin turns into bear skeleton with no tissues or spines, and most were devoured by predators as they were dying, unable to defend themselves.
According to estimates, today only a few individuals of the affected sea urchin species remained throughout the coral reefs of the Gulf of Aqaba.
Bronstein explained that sea urchins in general, and specifically diadematoids – the sea urchin family affected by the disease – are considered key species essential for the healthy functioning of coral reefs. Acting as the reef’s ‘gardeners’, the sea urchins feed on the algae that compete with the corals for sunshine and prevent them from taking over and suffocating the corals.
The most significant and widely studied mass mortality of sea urchins to date occurred in 1983, when a mysterious disease spread through the Caribbeans, killing most sea urchins of the species Diadema antillarum – relatives of Eilat’s sea urchins.
As a result, the algae spread uncontrollably, blocking the sunlight from the corals, and the entire reef was transformed from a coral reef into an algae field.
Even though the mass mortality event in the Caribbeans occurred 40 years ago, both the corals and the sea urchin populations never fully recovered, with repeated mortality events observed in the years since.
The latest Caribbean outbreak in 2022 killed surviving populations and individuals from the former mortality events. This time, however, researchers had the scientific and technological tools to decipher the forensic evidence.
A research group from Cornell University was able to identify the responsible pathogen in the Carribean, a scuticociliate parasite.
“This is a growing ecological crisis, threatening the stability of coral reefs on an unprecedented scale,” Bronstein warned.
“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.
“The deadly pathogen is carried by water and can affect vast areas in a very short time. Even sea urchins raised in seawater systems at the Interuniversity Institute for Marine Sciences in Eilat, or at the Underwater Observatory, were infected and died, after the pathogen got in through the recirculating seawater system.
“As noted, death is quick and violent,” Bronstein said. “For the first time, our research team was able to document all stages of the disease – from infection to the inevitable death – with a unique video system installed at the Interuniversity Institute for Marine Sciences in Eilat.
“In our study we 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. When we published our report last year, we already knew about 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 70 kilometers 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,” Bronstein said.
“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.”
Worse, as yet there is no cure.
Bronstein said there is currently no way to help infected sea urchins or vaccinate them against the disease.
“We must, however, quickly establish broodstock populations of endangered species in cultivation systems disconnected from the sea – so that in the future we will be able to reintroduce them into the natural environment,” he emphasized.
“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. 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.”
