- The long-spined sea urchin (Diadema antillarum) is a key algae grazer in the Caribbean. A disease outbreak in the 1980s killed off most of the urchins, resulting in the overgrowth of many Caribbean coral reefs with algae.
- Last year, a recurrence of the disease hampered the species’ slow recovery. This time, scientists were able to discover the culprit, which they revealed in a recent paper.
- The waters of Jamaica’s Oracabessa Bay Fish Sanctuary remained largely unaffected by the disease. Scientists there collected healthy long-spined sea urchins and started an urchin nursery in hopes of restoring the species on reefs around the island.
- This story was produced with support from the Pulitzer Center.
ORACABESSA BAY, Jamaica — An encounter with a long-spined sea urchin is fairly rare in the Caribbean these days, but not for Jaye James who is currently feeding chunks of pulpy green algae to a nimble trio. This group is one of eight she must feed every two days to keep them healthy and growing at this urchin nursery, housed in the Oracabessa Bay Fish Sanctuary on Jamaica’s northern coast. James places the lumps of algae close to the urchins or sometimes on their spines for easier access. They use the suction motion of their tiny tube-like feet to slowly move the algae around to their mouths, situated near the tank floor.
Algae is the urchins’ favorite food. And that’s why they are so important to the Caribbean’s marine ecosystem. “They help to keep the reef healthy and decrease the amount of algae, which competes with coral,” James, a marine scientist who manages the sanctuary and tends the urchin nursery, tells Mongabay.
The urchin’s prickly nature, defensive prowess and more than five million years of survival as a species make it hard to imagine this deep dweller as vulnerable. But in the 1980s, a disease struck Caribbean waters, nearly wiping out long-spined urchins (Diadema antillarum). Last year, the disease returned with the same devastating effect. As a result of the urchins’ low numbers, an excess of algae has stifled and killed healthy coral in Jamaica and the wider Caribbean. The implications ripple through coastal communities across the region, affecting the livelihoods of people who live from the sea. But the efforts to stem this destructive tide have produced some interesting solutions; namely, the sea urchin nurseries attempting to regrow the dwindling species.
Jaye James feeding chunks of pulpy green algae to a sea urchin. Video by Gladstone Taylor.
Fewer urchins, sicker corals
The health of the Caribbean’s beloved tropical waters has been deteriorating since the 1970s. Rising sea temperatures, ocean acidification, pollution, overfishing and the new stony coral tissue loss disease have contributed to the general decline of coral reefs and fish stocks. Roughly 10 years into this decline, the first urchin disease outbreak began in 1983 and swiftly killed off 98% of the Caribbean’s long-spined sea urchins before ending in 1984, according to a 2015 paper. Yet the identity of the pathogen responsible bewildered scientists for 40 years.
In 2022, another similarly lethal outbreak of the same disease struck, disturbing the sluggish 12% recovery of the urchin’s numbers that had taken place. The first signs occurred in February in St. Thomas, U.S. Virgin Islands, according to the Diadema Response Network (DRN) of the Atlantic and Gulf Rapid Reef Assessment, an international group of scientists that formed to track the outbreak. The disease soon appeared on other islands, including Dominica, St. Vincent, Barbados and Jamaica — at least 25 jurisdictions throughout the Caribbean, according to the DRN. The group is still assessing data and it’s unclear whether the die-off has abated.
This time, however, researchers were able to discover the biological perpetrator of the disease: a species of scuticociliate, a type of single-celled marine microorganism. They described the pathogen in a paper published in April. After being infected, urchins show rapid deterioration, the paper states. They lose their long calcified spines, their tube-like feet and other essential tissue, leaving them vulnerable to predatory fish. After first showing signs of disease, they can die within days.
While parrotfish often get credit for being the most important coral reef cleaners in the Caribbean, long-spined urchins are actually more aggressive algae grazers here. The depletion of their population has led to a slow and steady takeover of many reefs by the coral’s natural enemy, algae. According to a 2014 IUCN report, Caribbean corals have declined by 50% since the 1970s, with major consequences for the region’s marine food webs.
Baby years at the nursery
In November 2022, James put Oracabessa Bay Fish Sanctuary’s plan for an urchin nursery into action. The plan had been developed in 2020 as a way to boost wild urchin numbers under James’ predecessor, Inilek Wilmot. A grant from the United States Embassy brought the nursery off the idea shelf and into play.
The waters of Oracabessa Bay had only been affected by the disease on a small scale in 2022, and sanctuary staff gathered young, healthy urchins there to start the nursery. The method of caring for them is fairly simple: Feed them every two days, ensure the water in their tanks maintains the natural salinity of the sea and avoid exposure to excess rainfall. Currently Oracabessa’s nursery holds 24 urchins, three to a tank. They’re each about 200 millimeters (8 inches) in diameter, but long-spined sea urchins can grow up to 400 mm (16 in), so if more were cohabiting they could outgrow the tank and each other.
The nursery isn’t even a year old, and James says it’s still baby years. Her plan is to raise this batch of young ones to maturity, which could take four or five years, and then simulate the conditions for reproduction, which she says are “expensive and extensive,” requiring careful regulation of water temperature and aeration and specialized equipment during spawning and rearing of larvae. When they spawn, males release sperm, females release eggs and larvae are born right there in open water. In the sea, the larvae are swept to and fro by currents, but once they mature or find calm waters and places to lodge, they begin to grow out. At the Oracabessa nursery, James intends to collect the larvae and incubate them until they’ve developed enough to survive on their own before releasing them in the wild.
“Getting them to reproduce is difficult, but once we achieve that, our plan is to relocate them to other reefs in the area like Boscobel Fish Sanctuary where the population is lower,” James says.
As one of Jamaica’s oldest and most successful fish sanctuaries, Oracabessa is a beacon for marine conservation. Since its founding in 2010, the 75-hectare (185-acre) sanctuary has been a pioneer on the island for sea turtle protection, coral gardening and establishing sanctuary patrols. Not only has Oracabessa served as a model for others, like White River Fish Sanctuary in Ocho Rios, St. Ann, and East Portland Fish Sanctuary in Port Antonio, Portland — which have adopted its models for tourism and sanctuary co-management with community fishers — but it has also shared its access to support and the knowledge it’s gleaned from its marine projects. Coral gardening is a key example: It is one of Oracabessa’s primary projects, and other Jamaican marine protected areas have taken it up. Although Orcabessa’s urchin nursery is in its infancy, the goal is for urchin rearing to spread in a similar way.
So far, Oracabessa is the only urchin nursery in Jamaica, but there are others in the Caribbean. In Puerto Rico, Stacey Williams, a marine scientist with the nonprofit Institute for Socio-Ecological Research, runs two such nurseries. Since starting in 2014, her project has restocked some 5,500 captive-bred urchins to Puerto Rican reefs, where they quickly chew through overgrowing algae, according to El Nuevo Dia. Although the Jamaican and Puerto Rican operations do not officially collaborate, James says her plans are in many ways inspired by Williams’ research and nursery.
Scientists say they believe the disease is likely to return to the region and are considering other approaches beyond urchin nurseries to mitigate the effects, though they are in the early stages of ideation. Alyssa White, a master’s student in marine biology at the University of the West Indies’ Barbados campus who is studying the urchin die-off, says it’s possible the urchins will naturally develop immunity through natural selection.
“[Another] way to tackle this disease is a genetic modification approach that would improve the species’ resilience to the infection,” she tells Mongabay, adding that this remains entirely theoretical.
Although efforts to rehabilitate the D. antillarum population are in their incubatory phases, and the species has not yet undergone an extinction risk assessment for inclusion on the IUCN Red List, research is active. White says she believes the work of the DRN to track urchin health along with efforts to replenish wild urchin populations with nursery-grown babies can help turn the tide.
“With the work being done, it is creating grounds to support the argument that the species should be considered for registration under the IUCN Red List and undergo rehabilitation and restoration,” she says. “They play a crucial role in Caribbean coral communities.”
Banner image: Long-spined sea urchins, photographed at Flower Garden Banks National Marine Sanctuary off Texas in the Gulf of Mexico in 2014. Image by G.P. Schmahl/NOAA via Wikimedia Commons (Public Domain).
Hewson, I., Ritchie, I.T., Evans, J.S., Altera, A., …Breitbart, M. (2023). A scuticociliate causes mass mortality of Diadema antillarum in the Caribbean Sea. Science Advances, 9(16), DOI: 10.1126/sciadv.adg3200
Lessios, H. (2016). The great Diadema antillarum die-off: 30 years later. Annual Review of Marine Science, 8(1), 267-283. doi:10.1146/annurev-marine-122414-033857
Williams, S. M. (2021). The reduction of harmful algae on Caribbean coral reefs through the reintroduction of a Keystone herbivore, the long‐spined sea urchin Diadema antillarum. Restoration Ecology, 30(1). doi:10.1111/rec.13475
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