Sea urchin die-off threatens to destroy Eilat’s coral reef

Sea urchin die-off threatens to destroy Eilat’s coral reef

“Mass mortality of sea urchins in the Mediterranean Sea has spread to the Gulf of Eilat and threatens to destroy the coral reef,” warns a research team from Tel Aviv University, led by Dr. Omri Bronstein.

Sea urchins in general, and black sea urchins, called Diadema setosum, in particular, are essential to the proper functioning of coral reefs. Without them, a coral reef can become dominated and overwhelmed by algae.

This story began two decades ago, when these sea urchins invaded from the Red Sea to the Mediterranean Sea off the coast of Turkey. Brownstein and his team have been tracking the sea urchin invasion for around 15 years, including when the first one was discovered off Tel Aviv in 2016. Then, between 2018 and 2019, the situation began to change, and the small population of black sea invaders sea urchins grew exponentially.

“They have grown so large that in some sites in southern Turkey there are now populations of tens of thousands of individuals,” Brownstein explained. “It’s called a population epidemic.”

Brownstein and the team were preparing to file an article explaining why the Mediterranean environment was ripe for these species. But as they were finishing this report, they started hearing about mass sea urchin mortalities from colleagues in Turkey and Greece.

“As we worked on studies summarizing the invasion of sea urchins in the Mediterranean, we began to receive reports of sudden and large mortality,” Brownstein said. “Supposedly, the extinction of an invasive species is not a bad thing, but we need to be aware of two major risks: first, we don’t yet know how this mortality and its causes might affect local species in Mediterranean; and second, and much more critical, the geographic proximity between the eastern Mediterranean and the Red Sea could allow the pathogen to rapidly cross the natural Red Sea population. As we feared and predicted, it seems to have happened.

Disappearance of sea urchins in the Caribbean

Brownstein and the team immediately began following this story, and the first thing they noticed was that something seemed familiar to them about the situation. The massive mortality reminded the TAU team of the famous disappearance of sea urchins in the Caribbean.

“Until 1983, the Caribbean coral reef was a thriving tropical reef, quite similar to the coral reef in the Gulf of Eilat,” Brownstein said. “Once the sea urchins were gone, the algae grew out of control, blocked sunlight from reaching the corals, and the entire reef changed irreversibly – from a coral reef to a coral field. ‘algae.” A group of researchers from Cornell University have identified the cause of the mortality in the Caribbean: a pathogenic ciliated parasite.

The pathology seen in sea urchins dying in Greece and Turkey is identical to the pathology in the Caribbean, and this is also the pathology we see in sea urchins dying here in the Red Sea,” he said.

Brownstein described sea urchins as the “gardeners or lawnmowers” of the coral reef. As vegetarians, they eat copious amounts of plant matter, providing a balance that allows corals to thrive against algae. Unfortunately, the situation has not improved four decades after the Caribbean pandemic.

“At first we thought it was some kind of pollution or poisoning, or a spill of local chemicals, from industry and hotels in the northern Gulf of Eilat, but when we looked at other sites in Eilat, Jordan and the Sinai, we quickly realized that this was not a local incident,” Brownstein pointed out. “All of the findings pointed to a rapidly spreading epidemic. Similar reports are coming in from colleagues in Saudi Arabia.

“Even the sea urchins we keep for research purposes in our aquariums at the Interuniversity Institute and sea urchins in the marine park of the Eilat Underwater Observatory contracted the disease and died, probably because the agent pathogen entered through the pumping systems,” he continued. “It’s a quick and violent death: in just two days, a healthy sea urchin becomes a skeleton with massive tissue loss. While some corpses are washed up on shore, most sea urchins are eaten while they are dying and unable to defend themselves, which could accelerate contagion from fish that feed on them.

This week the first paper was published in Royal Society Open Science. A second report is expected to appear soon in Frontiers in Marine Science, and a third is on the way, Brownstein said. occurring in Jordan, Egypt, Saudi Arabia, Greece and Turkey.

The team also submitted their report and recommendations on emergency measures to save the coral reefs to the Nature and Parks Authority.

“We need to understand the seriousness of the situation: in the Red Sea, mortality is spreading at a staggering rate and already encompassing a much larger area than what we see in the Mediterranean,” Brownstein said. “In the background, there is still a big unknown: what really kills sea urchins? Is it the Caribbean pathogen or some new unknown factor? Either way, this pathogen is clearly waterborne, and we predict that in a short time, the entire population of these Mediterranean and Red Sea urchins will become ill and die.

“In my view, we urgently need to establish a broodstock population for these sea urchins so that, if necessary, we can release them back into the wild in the future,” he said. “As with COVID-19, at this point no one knows what will happen – will this epidemic go away on its own, or will it stay with us for many years and cause a dramatic change in coral reefs? However, unlike the COVID-19 pandemic, in this case we have no way to vaccinate or treat sea urchins, so we must focus all of our efforts on prevention.

Brownstein warned that the window for preserving a healthy population of this species in Eilat has already closed, and if a brood stock is to be established, it had to be done yesterday.

“It’s a complex task, but absolutely necessary if we are to ensure the survival of this unique species that is so critical to the future of coral reefs,” he said. “The question is: will the decision makers be faster than the disease? I do my best to make it happen. »

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