The vibrant coral reefs of the Red Sea have long been a dazzling underwater paradise, boasting a stunning array of marine life, including beautiful fish. Despite the challenges posed by climate change, these reefs have exhibited remarkable resilience to rising sea temperatures. However, a recent mysterious decline in a critical species of sea urchins is now threatening this precious habitat, raising concerns that fast-growing green algae may choke the reefs, leading to potential devastating impacts on tourism.
Israeli researchers first noticed the deaths of black sea urchins near Eilat, a southern city, at the beginning of the year. These spiky creatures, recognisable for their defensive spines up to 50cm long, have been a familiar sight for scuba divers and snorkelers who visit the Gulf of Aqaba for its clear waters. They used to carpet parts of the coastal reefs in the region.
Recent surveys indicate a troubling 90% reduction in the Jordanian resort of Aqaba, widespread disappearances in Egypt, and losses in Saudi Arabia, likely caused by a waterborne parasite.
“We know the pathogen hurts,” says Dr Omri Bronstein at Tel Aviv University, placing a dead black sea urchin – its body the size and shape of a flattened tennis ball – into my hands.
He states that there are visible signs that the disease paralyses the sea urchin’s spines and tiny feet.
“You see what we call necrosis, losing tissue, until you get a bare skeleton. And their mortality is very rapid; the entire process takes about 48 hours.”
Videos captured by scuba divers show how infected black sea urchins, without their defensive spines, quickly fall prey to predatory fish. Human activities, particularly shipping, may have played a role in spreading the disease.
The consequences of this sea urchin decline could have a profound ecological impact on one of the world’s oldest continuously living reefs in the Red Sea, estimated to be over 5,000 years old. Sea urchins play a crucial role in coral growth by aiding the settlement of coral larvae and by consuming algae, preventing it from blocking sunlight and overpowering the corals.
“Sea algae and corals are always competing for space,” explains Omri Omessi, a maritime inspector for the Israel Parks and Nature Authority who is based in Eilat.
He says sea algae will spread much faster once the urchins are gone: “Sea algae can spread way faster than corals. Corals, as we know, can grow an average of 1cm in one year. Sea algae can grow 1cm in a day!”
To illustrate the speed with which the disease has spread, he recounts a personal story of taking a diving holiday in Nuweiba in Egypt, about 80km (50 miles) to the south, after he had begun monitoring the loss of the black sea urchins in the very north of the Gulf of Aqaba.
He recalls seeing thousands of black sea urchins in Egypt and thinking “everything may be OK”.
“But two weeks later, the people there told me that if I went back to Nuweiba, I would not find even one [of the urchins]. This is really, really violent. It’s really, really fast.”
Further south along the Egyptian Red Sea coast, marine biologist Dr. Mahmoud Hanafy from Suez Canal University has been conducting his own studies, which indicate that the species is disappearing across the region.
“Before you would easily find 20 to 30 per sq m (10.7 sq ft),” he tells me. “Now the black sea urchin disappeared from all the areas I surveyed north of Hurghada to south of Marsa Alam. I could not find a single specimen.”
Other nearby countries have also experienced significant die-offs of sea urchins, including Jordan and Saudi Arabia.
There are varying opinions among scientists regarding the potential consequences of this decline. Some argue that their reefs do not seem to be immediately impacted by the sea urchin disappearance, as other marine animals continue to support the corals.
However, others fear a situation similar to what occurred 40 years ago in the Caribbean, where a pathogen wiped out up to 99% of a closely related species of sea urchin, leading to a thriving coral reef being transformed into an algae-covered landscape. The true effects in the Red Sea may not be apparent until winter when algae blooms naturally occur.
Despite the concerns, there are hopeful signs. Researchers in Tel Aviv have been studying black sea urchins in the Eastern Mediterranean for about a decade, following their appearance from the Red Sea as an invasive species. While these populations were the first to be affected by the recent die-offs, some healthy pockets of sea urchins remain, which could potentially become a broodstock, kept in captivity for eventual reintroduction into their native environment. Additionally, a few young urchins have been observed in the Gulf of Aqaba and are being closely monitored.
While individual countries are taking steps to address overfishing and pollution, which pose their own risks to coral reefs, there is also encouraging cooperation in this politically complex region, where Saudi Arabia and Israel do not have formal diplomatic ties. Countries are sharing information and working together, even if such cooperation is not always publicised.
“The distances between Israel, Jordan, Egypt and further south don’t really exist under water,” Dr Bronstein says.
Despite the differences among the countries bordering the Red Sea, the fate of the black sea urchin illustrates their shared interest in preserving this unique marine environment. Efforts to understand and address the decline of this species hold the potential to safeguard the beauty and biodiversity of the Red Sea’s coral reefs for future generations.
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