The entire population of black sea urchins living on coral reefs off the southern city of Eilat has been wiped out in just weeks by a suspected pathogenic parasite, in what an expert warned Wednesday could cause irreversible reef damage.
Dr. Omri Bronstein of Tel Aviv University, whose research team is following the phenomenon, predicted that within a short time, all of these sea urchins, in both the Mediterranean and the Red Sea, will get sick and die.
Reports of mass die-offs have also come from other Red Sea countries, such as Egypt and Saudi Arabia.
Initial observations suggest that the so-called banded urchin (Echinothrix calamaris) is also experiencing mass mortality.
Sea urchins in general, and both black (Diadema setosum) and banded urchins in particular, perform the critical role of reef “gardeners.” They feed on algae and prevent them from taking over and suffocating the corals, which compete with them for sunlight.
Bronstein’s research team from Tel Aviv University’s School of Zoology and the Steinhardt Museum of Natural History has sent an urgent report to the Israel Nature and Parks Authority, where emergency steps for saving the coral reefs are currently being considered.
Bronstein, who likened the outbreak to the early days of COVID-19 when nobody understood what was happening, proposed the immediate establishment of a black sea urchin breeding program to so that the creatures that could be returned to nature if and when needed.
Dr. Assaf Zvuloni, Eilat District ecologist for the Israel Nature and Parks Authority, said, “This is a warning light for the vulnerability and sensitivity of Eilat Bay’s ecosystem to environmental changes, many of which are currently caused by humans.”
He called on all the bodies that deal with the Eilat Bay to convene to discuss how to restrict the flow of nutrients, such as fertilizer run-off, into the sea. These encourage the growth of algae.
Coral expert Prof. Maoz Fine, of Jerusalem’s Hebrew University and the Eilat Interuniversity Institute for Marine Sciences, said urchins in his experimental tanks had also died.
He said it was critical for Jordan and Egypt, as well as Israel, to limit nutrient flow into the sea, and perhaps even to temporarily ban fishing species of fish that graze on algae.
In terms of wealth and biodiversity, coral reefs are considered to be the underwater “rainforest”’ of the planet.
But with sea temperatures rising, many are dying.
Eilat’s corals have worldwide importance because they have proven to be unusually robust, not yet not showing the fatal signs of bleaching seen in reefs elsewhere in the world.
But they still face multiple threats, from tourist development to fertilizer and pesticide runoff and oil pollution.
Diadema sea urchins are native to a vast tropical area from East Africa and the Red Sea through the Indian Ocean to Japan and the South Pacific Islands.
Since 2006, though, they have also colonized much of the Mediterranean Sea, where they are regarded as invasive species. It is thought that they got there via the Suez Canal, which links the Mediterranean with the Red Sea.
From Turkey, the species has spread along the coasts of Greece, Lebanon, and Israel, down to Egypt and Libya.
Bronstein’s research group has been focusing on the invasive urchins in the Mediterranean. For reasons that remain unclear, populations in Greece and Turkey have grown exponentially over the past five years, and it is there that mass die-offs of other urchin species are now taking place.
He and his team were the first to identify this mass mortality, and had warned in an academic paper due to be published this week that the phenomenon could spread to the Red Sea.
Bronstein’s group is rushing to determine whether the parasite affecting the urchins in the Gulf of Eilat is the same one that has decimated urchins in the Caribbean, where reefs similar to those in Eilat once flourished.
“Once the sea urchins disappeared there, the algae multiplied without control, blocked the sunlight from reaching the corals, and the entire reef changed irreversibly — from a coral reef to an algae field,” Bronstein said. “Last year the disease broke out again in the Caribbean, killing the surviving urchin populations and individuals.”
The first reports of mass mortality in the Gulf of Eilat came in December.
“At first we thought it was some kind of pollution or poisoning or a local chemical spill from the industry and hotels in the north of the Gulf of Eilat,” Bronstein said.
‘Whatever is killing them is doing so violently and thoroughly’
“But when we examined additional sites in Eilat, Jordan, and Sinai, we quickly realized that this was not a local incident. All findings pointed to a rapidly spreading epidemic. Similar reports are coming in from colleagues in Saudi Arabia,” Bronstein said.
“Even sea urchins that we grow for research purposes in our aquariums at the Interuniversity Institute, and sea urchins at the Underwater Observatory Marine Park in Eilat, contracted the disease and died, probably because the pathogen got in through the pumping systems.”
“Whatever is killing them is doing so violently and thoroughly. It can travel vast distances over very short periods, and it will kill a healthy adult sea urchin within 48 hours,” he said.
“While some corpses are washed ashore, most sea urchins are devoured while they are dying and unable to defend themselves, which could speed up contagion by the fish who prey on them.”
The mass die-offs were unprecedented in three ways, he added. They were firsts for these species, for urchins in the Mediterranean, and for those in the Red Sea.
Bronstein said that there was no evidence of mortality in the Israeli Mediterranean yet.
This provided “a very narrow window of opportunity” to act, and — ironically — to use the invasive urchins to breed for possible reintroduction into their native habitat in the Red Sea in the future. Both come from the same genetic group.
“We must understand the seriousness of the situation: in the Red Sea, mortality is spreading at a stunning rate, and already encompasses a much larger area than we see in the Mediterranean.”
“As with COVID-19, at this point no one knows what will happen,” he said. “Will this epidemic disappear by itself, or will it stay with us for many years and cause a dramatic change in coral reefs?
“This pathogen is clearly carried by water, and we predict that in just a short time, the entire population of these sea urchins, in both the Mediterranean and the Red Sea, will get sick and die.”
Fine noted that as sea urchin populations tended to have “boom and bust” years, they could recover, but said the worry was what would happen to the reefs in the meantime in terms of algae cover.
Without the algae grazers, and until the urchin population came back, he said, it was critical to control the flow into the Red Sea of nutrients coming from sources such as sewage and desalination plants, and marine and terrestrial agriculture.
Asked about the worst-case scenario for the Gulf of Eilat, Fine said the algae could take over and kill the reefs for a few years until the urchins bounced back.
Neither Fine nor Bronstein could say whether oceanic warming was connected to the mass die-offs. Fine pointed out that they did not happen in summer.
The studies were led by Bronstein and PhD students Rotem Zirler, Lisa-Maria Schmidt, Gal Eviatar, and Lachan Roth from the School of Zoology, Wise Faculty of Life Sciences, and The Steinhardt Museum of Natural History at Tel Aviv University. Papers are being published in Frontiers in Marine Science and Royal Society Open Science.