Black sea urchins have disappeared from the Gulf of Aqaba. Their loss could kill an entire reef | Cnn

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Eilat, Israel
Cnn

Under the bright blue water of the Gulf of Aqaba on the Red Sea, the view is stunning. Extensive coral reefs teeming with life; colorful fish and invertebrates. But something crucial has disappeared from this beautiful scene and that could threaten the entire ecosystem.

Black sea urchins.

In January, scientists at Tel Aviv University’s Eilat Interuniversity Institute of Marine Sciences noted that within days, the entire population of black sea urchins in the northern part of this gulf was gone.

These jet-black, round-bodied, long-spiked creatures might be best known for their painful stings. But they are also a crucial part of the ecological system of these coral reefs. Without them, coral reefs are at risk.

Dr. Omri Bronstein leads the team of researchers here. He says he received a panicked phone call from his doctoral students one January evening after they had taken a regular nighttime monitoring dive.

They came out of the water, still in their diving suits. And they called and said, “Listen, there’s something really weird about our site, the sea urchins are completely gone,” Bronstein said. It was shocking. It was just shocking, because this is a site we know intimately well, over the past five years. And we’ve never seen any fluctuation on that magnitude.

Bronstein and his team quickly realized that whatever was killing the sea urchins, most likely a waterborne pathogen, was doing it rapidly. And it is spreading in waters off the coast of countries in the region, including Jordan, Egypt, Saudi Arabia, Greece and Turkey.

It takes 48 hours for an individual to go from a living, healthy individual to a virtually bare skeleton, Bornstein said, adding that urchins vanish almost entirely within a day because their remains mostly break down in water.

The outbreak affects only black sea urchins and was even killing them in tanks at Eilats’ research laboratories and aquarium, all of which use freshly circulating seawater.

We know it’s transmitted through water, they don’t need direct contact, Bronstein said.

The tanks are now covered in the algae that sea urchins normally eat.

When we visited, a lone juvenile sea urchin remained in tanks that once housed dozens of them. But these creatures are the kind that can only survive in large numbers.

When you see an individual, or even a few individuals, even when they survive, that’s not enough to sustain a population. There is a critical minimum size, the population size needed to maintain a thriving population, Bronstein said. Also, one of the strategies of this species in terms of protection [from predators] is that they normally form aggregations of dozens, and sometimes even in the past hundreds of individuals. And then by creating this cushion of thorns, basically, they provide protection for the whole group. When you are alone, your chances are not that good.

Beachgoers can be relieved that they don’t have to worry about stepping on their toes. But the disappearance of urchins is incredibly dangerous for unique coral reefs here and elsewhere in the Mediterranean region.

Black sea urchins feed on the algae that grow on the reef. Bronstein said they’re sometimes called the sea gardeners for this reason. Algae compete with corals for sunlight. So by eating it, the urchins give the corals a chance to grow, rather than being suffocated by algae, which has a much faster growth rate than coral.

There’s nothing we can do by hand to get rid of algae, even in the lab, Bronstein said. So now it’s not just the sea urchins themselves that are harmed, but the entire network in our lab or in the sea that relies on these crucial components.

A similar pathogen killed 98 percent of the Caribbean’s black sea urchin population in the 1980s and apparently returned to the Caribbean in 2022. That may be where the Red Sea pathogen came from, Bronstein said.

There’s a good chance there was some shipping-based transportation that actually basically helped this pathogen jump across the entire Atlantic, Bronstein said. The other assumption that hasn’t been outdated yet is that we may be dealing with a pathogen that has always been here or has been in the environment for many years. And for some reason, something changed and it made it more violent and caused the deaths we see today.

The threat to the Red Sea’s coral reefs isn’t just a threat to a beautiful site. These coral reefs are unique in the world for their ability to withstand high temperatures, which cause coral bleaching and the effects of climate change.

Omri Omesi, a marine ranger with the Israel Nature and Parks Authority, called the situation a catastrophe not only for this gulf, but potentially for all of Earth’s coral reefs.

This is one of the northernmost tropical coral reefs in the world, this is actually a miracle that they exist, Omesi said. It’s very, very important to keep this place going because it gives hope for other reefs in the world. We can find out why we have this resistant coral bleaching.

An important aspect of Bronstein’s team’s research is studying the environmental DNA of water. Without the need for more invasive methods, DNA analysis can also help predict what might be happening such as another epidemic and reproductive activity before researchers can physically see it.

Given how quickly the urchins disappeared, Bronstein said scientists have little time to act. His team skipped the normal academic process that can take months or years to conduct studies and publish journal articles, choosing to sound the alarm as quickly as possible with fast-paced academic papers and public appeals.

We need to understand, and decision makers need to understand, that the window of opportunity for action is very, very narrow. And it’s closing fast, Bronstein said.

The first step, which is needed in the coming weeks, is to establish spawning populations that will ultimately help repopulate and reintroduce black sea urchins to the region. But the surviving sea urchins that could be used to do so are themselves under threat.

[The mass mortality] it is currently occurring south of Turkey and Greece, but is moving down the eastern Mediterranean coast, towards Syria, Lebanon and Israel. Once we get there, we’ll probably have pretty much closed our window of opportunity to take action, Bronstein said.

Bronstein said he has been in constant contact with government agencies and other researchers in the region.

Israel shares the gulf with Jordan, Egypt and Saudi Arabia, with whom it has no formal relations. But underwater there is no such thing as politics, and Bronstein said international cooperation will be key to solving that problem.

It’s our mandate, it’s our responsibility to make sure we do everything we can to make sure these reefs, these unique reefs, probably the most unique reef in the world, it’s our responsibility to make sure they stay here for future generations, Bronstein said.

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