A dying D. Setosum Sea Urchin (Courtesy of Tel Aviv University)
In really upsetting and disturbing news, the entire population of black sea urchins in Eilat was wiped out over a couple of months. This is an environmental and ecological disaster, not to mention something that will surely harm the tourism industry in Israel’s southernmost city.
Eilat is known for its coral reef. The reef is located down the shore from the city, about half of the way to the border with the Sinai. Black Sea urchins live around reefs. They come out at night and are best known for their long black and sharp spines like those on a porcupine. Bathers are warned not to touch them as their sting is painful.
Sea urchins in general, and black sea urchins specifically, are considered key species essential for the healthy functioning of coral reefs. Following the discovery of their deaths, an urgent report describing the current situation was submitted to the Israel Nature and Parks Authority, and emergency steps for saving the coral reef are now being considered.
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A series of new studies conducted by researchers from Tel Aviv University revealed a deadly epidemic causing mass mortality of black sea urchins in the Mediterranean Sea and the Gulf of Eilat. For example, thousands of sea urchins living in a site near the northern shore of the Gulf of Eilat died out over the course of only a few weeks. The epidemic was so severe, said the researchers, that today no living black sea urchins have remained at the site, only skeletons. The same has happened at other sites in the Gulf of Eilat. The studies note that such extensive mortality is also occurring in other countries in the region, including Jordan, Egypt, Saudi Arabia, Greece, and Turkey.
The researchers emphasize that sea urchins in general, and the long-spined Diadema setosum in particular, are considered key species essential for the healthy functioning of the coral reef. The researchers: “It must be understood that the threat to coral reefs is already at an all-time peak, and now a previously unknown variable has been added. This situation is unprecedented in the entire documented history of the Gulf of Eilat.”
The researchers assume that the source of the deadly epidemic is a pathogenic ciliate parasite that has spread from the Mediterranean to the Red Sea. An urgent report describing the current situation was submitted to the Israel Nature and Parks Authority, and emergency steps for protecting Israel’s coral reefs are now under consideration.
The studies were led by Dr. Omri 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. The papers were published in Frontiers in Marine science and Royal Society Open Science.
Dr. Bronstein explained, “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, 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. “
Bronstein said that there are similar reports are coming in from his colleagues in Saudi Arabia, adding that even sea urchins the scientists grow for research purposes in 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.
“It’s a fast and violent death,” he described, “within just two days a healthy sea urchin becomes a skeleton with massive tissue loss. 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 first reports on mass mortality reached Dr. Bronstein several months ago, from colleagues in Greece and Turkey, which the sea urchins had invaded, probably through the Suez Canal.
“In 2006 the first sea urchin of this species was discovered in the south of Turkey,” adds Dr. Bronstein. “This phenomenon, known as biological invasion, has extensive ecological implications, and is widespread in the eastern Mediterranean, especially along Israel’s coastline. We have been tracking the dynamics of this species’ invasion in the Mediterranean since its first appearance. In 2016 we discovered the first Diadema setosum sea urchin along Israel’s Mediterranean coastline – a single urchin at the Gordon Beach in Tel Aviv. For over a decade since the first discovery in Turkey, populations in the Mediterranean remained small and usually hidden.”
But since 2018 the sea urchin population in the Mediterranean has been growing exponentially, reaching a state of population explosion – with giant populations of thousands and even tens of thousands found in Greece and Turkey. However, the researchers said that as they worked on studies summarizing the invasion of sea urchins in the Mediterranean, they began to receive reports on sudden extensive mortality.
“Supposedly the extinction of an invasive species is not a bad thing,” said Bronstein, “but we must be aware of two major risks: First, we don’t yet know how this mortality and its causes might impact local species in the Mediterranean; and second, and much more critical, the geographic proximity between the eastern Mediterranean and the Red Sea might enable the pathogen to quickly cross over to the natural population in the Red Sea. As we feared and predicted, this is what appears to have happened.”
Dr. Bronstein’s studies were the first to identify mass mortality in an invasive species in the Mediterranean, and also the first to indicate mass mortality of sea urchins of the species Diadema setosum – one of the world’s most common species of sea urchins. Dr. Bronstein concluded one of these groundbreaking studies with a warning – that the epidemic breaking out in the Mediterranean might spread to the nearby Red Sea. Unfortunately, this warning has come true.
“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. In the background there is still a great unknown,” he said. “What is actually killing the sea urchins? Is it the Caribbean pathogen or some new unfamiliar factor? Either way, 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.”
