Global coral reefs at risk as pathogen decimates red sea urchins
Israeli researchers have identified the pathogen responsible for a deadly epidemic that has been decimating sea urchin populations in the Red Sea.
The beaches of the Red Sea in Eilat on a winter day on Dec. 20, 2021. Photo by Keren Perelman/TPS
The study, which began with observations in Eilat, now indicates a global threat to coral reef ecosystems, stretching from the Red Sea to the Indian Ocean.
Sea urchins, often dubbed the “gardeners” of coral reefs, play a critical role in maintaining the balance of these delicate ecosystems by feeding on algae that compete with corals for sunlight. The sudden and rapid decline of the essential urchins poses a dire risk to coral reefs worldwide.
A team of Tel Aviv University researchers led by Dr. Omri Bronstein first detected the epidemic in December 2022. They have since identified the pathogen: a scuticociliate parasite similar to another parasite that wiped out large numbers of urchins in areas between the Caribbean and Florida. This pathogen is now spreading rapidly among the Red Sea’s population of urchins (Diadema setosum) with devastating effects.
“Since the outbreak, we’ve observed the near-complete annihilation of sea urchin populations in the affected areas,” said Bronstein. “What began as a localized issue has transformed into a global crisis, threatening coral reefs on an unprecedented scale.”
Coral reefs act as nurseries and habitats for countless marine species, providing shelter, food, and protection from predators. They also serve as a natural barrier, reducing coastal erosion and buffering against storm damage. Coral reefs also trap carbon that would otherwise be released into the atmosphere, helping mitigate the impact of climate change.
Rising sea temperatures, pollution, overfishing, and human activities already pose significant challenges to the survival of the reefs.
The team’s findings, published in the peer-reviewed Current Biology journal, reveal that the epidemic has spread across thousands of kilometres of coral reefs, from the Red Sea to Oman and as far south as Reunion Island in the Indian Ocean. The disease acts quickly and lethally, often killing a healthy sea urchin within two days and leaving only skeletal remains.
Bronstein and his team utilized molecular-genetic tools to pinpoint the parasite responsible. Their work builds on previous research that linked similar pathogens to the sea urchin die-offs in the Caribbean, which had catastrophic long-term effects on coral reefs there. The Caribbean outbreak of 1983 transformed vibrant coral ecosystems into algae-dominated zones, a shift from which the reefs have never fully recovered.
The current situation in the Red Sea mirrors this grim scenario. “Sea urchins from the genus Echinothrix, which were once abundant, have nearly vanished,” said Bronstein. The pathogen’s spread appears facilitated by human activities, notably shipping routes. For example, the wharf in Nuweiba, Sinai, where ferries from Aqaba dock, has been identified as a critical point in the spread of the epidemic.
The underwater scene in affected areas is described as surreal. “We’ve documented thousands of sea urchin skeletons littering the seabed, crumbling and disappearing swiftly,” Bronstein said.
There are no known method to treat or vaccinate infected sea urchins. The researchers emphasize the urgent need to raise healthy urchins in captivity that can eventually be reintroduced to their natural habitats.
But Bronstein and his colleagues are more focused on uncovering what triggered the outbreak. “We need to determine whether the pathogen was transported by seacraft or if it has always been present, with recent environmental changes triggering its virulence,” he explained.
“While we cannot repair nature, we can change our behavior. Understanding the causes and mechanisms of this outbreak is crucial. By protecting these essential species and their habitats, we safeguard the future of coral reefs globally.”
