We share its importance for the future well-being of the marine ecosystem of this region of the world.

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Characteristics

D. antillarum is an active herbivore at night, whose diet varies according to the environment and includes various algae: mats, endoliths, crustose coraline, macroalgae, seagrass and silty detritus. The species has a rounded and slightly flattened "carapace", with fine and hollow spines that can measure up to 30 cm, providing defense and facilitating locomotion. The total diameter can exceed 50 cm. The spines are usually black, but occasionally may be gray or white. Juveniles exhibit a black and white pattern, which sometimes persists in adults. In the aboral part of the "carapace", five pairs of blue iridescent bands can be observed that delimit the ambulatory plates, connecting the pole of the "carapace" to a disc under the anus. There is also a visible anal papilla, often black but sometimes gray.

Where do they live?

Diadema antillarum lives in the shallow waters of the Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. It is found in diverse habitats such as coral reefs, hard bottoms, debris, rocks, seagrass meadows, mangrove roots and tidal pools, as well as in dams and other structures created by humans.

History and decay

Historically, the sea urchin D. antillarum has been considered one of the most important macroalgae herbivores in the region, being its even greater relevance due to the reduction of the abundance of key herbivorous fish due to massive overfishing. Before 1983, D. antillarum was the most abundant herbivore in the Caribbean coral reefs. In January 1983, it experienced massive mortality at the Atlantic entrance to the Panama Canal, stretching along the coast of Central America, Bermuda, Jamaica, Venezuela, Barbados and the Lesser Antilles. Mortality spread eastward, affecting the Bahamas, Puerto Rico, La Española and the Virgin Islands. In two weeks, between 93% and 100% of the individuals on each reef were dead. Although the cause was never identified, the disorderly spread suggests a water-borne pathogen.

The disappearance of D. antillarum sea urchins had immediate effects on coral reef communities in the Caribbean. Macroalgae proliferated, reaching densities that resulted in the death of adult coral colonies. Although some sea urchins survived, they could not control algal blooms. In the long run, the near extinction of this herbivore, especially in areas without herbivorous fish, has contributed to significant reductions in living coral cover, being replaced by algae, aggravated by other stressors on the reefs.

Starting at the end of January 2022, a new mortality event in sea urchins emerged. The impact was initially detected in St. Thomas and, by the end of March, it had spread to other areas of the Caribbean, including the Lesser Antilles, Jamaica and the Mexican Caribbean. As of June 2022, cases of the condition were recorded in most of the Greater Antilles, Florida and Curaçao.

Coral reefs in the Caribbean show low diversity, with only 28% of the fish diversity and 14% of the coral diversity compared to other global hotspots. This lack of diversity makes reefs less resilient.

Did you know?

Despite its near extinction, the sea urchin is a marine species that is closely monitored to avoid possible catastrophes. The Diadema Map, created by AGGRA and collaborators, plays a crucial role in providing information on the location of sick or dying sea urchins in the Caribbean. It is essential to note that if you find a Diadema in this region, we encourage you to enter the website. There, you will have access to a form that allows you to notify and contribute to the understanding of the situation of this species. Sightings are marked in purple to indicate the first encounter. If the sea urchin population is in healthy condition, the marker will be green; however, if they are sick or dead, the marker will turn red.

A collective value

D. antillarum after the mass mortality event of 1983 continues to have a slow and uneven recovery process. However, as human beings it is our duty to continue to monitor and care for this species. The decrease in their populations can be stopped, to avoid an ecological catastrophe.

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