Deadly pathogen that wiped out Eilat’s sea urchins reaches Indian Ocean

Facing fears of global epidemic, Tel Aviv University scientists, who first identified local die-off and specific pathogen, are working with regional partners to understand more

Sue Surkes is The Times of Israel's environment reporter

Swaths of sea urchin skeletons washed up on the shore. (Jean-Pascal Quod)
Swaths of sea urchin skeletons washed up on the shore. (Jean-Pascal Quod)

Scientists at Tel Aviv University have discovered that a deadly epidemic that has wiped out Eilat’s most ecologically important sea urchins has spread across the Red Sea and into the Indian Ocean, threatening to become a global pandemic.

Sea urchins are the ‘gardeners’ of coral reefs, feeding on algae that compete with the corals for sunshine and preventing them from taking over and suffocating the corals. Roughly a quarter of all marine life, including over 4,000 fish species, rely on coral reefs at some point in their life cycle.

The Diadema genus being infected is one of the most abundant throughout the tropics and the violent pathogen, which can turn a healthy sea urchin into a skeleton within a couple of days, is carried by water.

A year ago, a research team led by the university’s Omri Bronstein found that the entire black sea urchin population living on coral reefs off the southern city of Eilat had been wiped out in weeks. Sea urchins at Eilat’s Interuniversity Institute for Marine Sciences and in tanks at the city’s underwater observatory also died after the pathogen entered the recirculating seawater systems.

Comparing a healthy sea urchin with the skeleton of an infected urchin. (Tel Aviv University).

At that time, reports of mass die-offs had also come from other Red Sea countries, such as Egypt and Saudi Arabia.

According to Bronstein’s team, who documented all stages of the disease, the two species of sea urchins once dominant in the Gulf of Eilat — the black urchin (Diadema setosum) and the banded urchin (Echinothrix calamaris) — have vanished.

The research team. (Tel Aviv University).

Using molecular-genetic tools, the researchers have identified the pathogen as Philaster apodigitiformis, the same one responsible for the mass die-off of the long-spined (Diadema antillarum) sea urchin in the Caribbean about two years ago (identified by Cornell University researchers).

The worst and most widely studied mass mortality of sea urchins occurred in the Caribbean in 1983 and neither the corals nor the sea urchins have fully recovered, with additional die-offs over the years.

Four healthy urchins on Reunion Island. (Jean-Pascal Quod)

“Apparently, the mass mortality we identified in Eilat in 2023 has spread along the Red Sea and beyond — to Oman, and even as far as Reunion Island in the Indian Ocean,” Bronstein said. far beyond what one would expect in terms of geography,

He told the Times of Israel that two doctoral students were analyzing two years of data related to DNA in the Gulf of Eilat’s seawater, collected as part of a separate project by his team. This would help ascertain which of two hypotheses is right: Did the pathogen reach the northern Red Sea from the Caribbean? Or has it always existed there, where something — such as climate change — caused it to become violent or affected the immunity of the Diadema genus?

He added that transport of the pathogen could be from boats and ships, water currents, or fish eating the infected sea urchins.

A ship docks at Aqaba Port in Jordan, (Xavi Talleda – Flickr: the transporter, CC BY 2.0, WikiMedia Commons)

“We know it started in our region and moved south quickly along Red Sea transportation routes,” Bronstein said, adding that the team knew it was already in the Jordanian port of Aqaba, next to Eilat, before it reached the Sinai peninsula.

“The first spot where we identified mortality in Sinai was next to a small port in Nuweiba, which received ferries from Aqaba. Two weeks later it reached Dahab, about 70 kilometers (43 miles) further south,” he recalled. The researchers reached Dahab as the pathogen arrived, and witnessed a healthy urchin population turn into carcasses.

“We can’t heal the sea by giving it medicine,” he continued, “but we can limit the damage we cause.”

The research could help manage the disease, he said. For example, if transportation was pinpointed as the cause, a ship’s ballast water could undergo DNA analysis before emptying.

Bronstein has called for rapidly breeding endangered sea urchins in systems disconnected from the sea for potential future reintroduction into the natural environment.

Asked whether other creatures could replace the Diadema urchins, Bronstein explained that each urchin species ate different things on the reef. Urchins from other groups whose numbers appeared to be increasing, ate less algae and could become problematic because, while grazing, they broke tiny bits of the hard coral substrate, helping to cause reef erosion.

Tropical fish at the Eilat Dolphin Reef. (Asaf Zvuloni/ Israel Nature and Parks Authority/FLASH90)

Some had suggested that fish might replace the diadema urchins, but Bronstein says that while a large algal bloom could develop in weeks, it would take years for fish populations to grow sufficiently large to eat all the algae. Furthermore, while fishing in the Gulf of Eilat was regulated, overfishing was the norm in the Red Sea and the Indian Ocean.

Bronstein’s team is working with other researchers in Europe and the region to analyze the effect on the Red Sea corals of the urchin die-off. “The Diadema urchins have not returned to the Gulf of Eilat. We counted a handful only. And we know that the mortality in the Red Sea was higher than in the Caribbean,” he said. “We are starting to see the effect on algal cover of the coral reefs.”

An infected sea urchin on Reunion Island. (Jean-Pascal Quod)

Eilat’s corals have worldwide importance because they have proven highly robust to rising sea temperatures, not yet showing the fatal signs of bleaching seen in reefs elsewhere.

Illustrative: Bleached coral in Guam in 2017. A study released in 2018 found that severe bleaching outbreaks are hitting coral reefs four times more often than they used to a few decades earlier. (David Burdick/NOAA via AP)

But they still face multiple threats, from tourist development to fertilizer and pesticide runoff and oil pollution.

The study was led by 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 the Steinhardt Museums’ Tamar Feldstein-Farkash.

The alarming results were published on Thursday in the scientific journal Current Biology.

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