How Can the National Coral Reef Monitoring Program Help Understand Long-Spined Sea Urchin Die-Offs?

by Erica K. Towle, Ph.D., National Coral Reef Monitoring Program Coordinator

The Caribbean may be facing a widespread die-off of sea urchins. Diadema antillarum, also known as the long-spined sea urchin, is one of the most important herbivores on Caribbean coral reefs because they eat algae, reducing algal overgrowth on the seafloor, which in turn provides reef area for coral growth. Diadema antillarum previously experienced a massive die-off throughout the Caribbean in the 1980s. In February 2022, scientists learned of extensive Diadema antillarum die-offs in St. Thomas, U.S. Virgin Islands (USVI). Since February, additional mortality events have been observed in St. John and St. Croix (USVI), Puerto Rico, and other Caribbean islands. Scientists do not know what is causing these die-offs, and the speed at which large numbers of sick urchins are dying resembles the mortality event of the 1980s. NOAA and our partners are worried that a crisis is occurring in the Caribbean, where stony coral tissue loss disease has already caused widespread coral mortality beginning in 2014.

Left figure shows an underwater image of a black sea urchin with many long, protruding black spines. Right figure shows an underwater image of a sick black sea urchin that has lost many of its spines, showing some white flesh.
Left: A healthy live Diadema has black spines all over its body. Right: A sick Diadema loses its spines. Credit: Kimani Kitson-Walters.

NOAA's National Coral Reef Monitoring Program (NCRMP) is a strategic framework for evaluating biological (fish, corals, and benthic communities), climatic, and socioeconomic indicators of coral health in U.S. coral reef areas. These data provide a robust picture of the status and trends of U.S. coral reefs and the human communities connected to them. NCRMP collects information on coral condition (including disease presence or absence), benthic cover, habitat composition, and reef complexity. In the Atlantic and Caribbean, NCRMP also collects information on key invertebrates like Diadema antillarum.

Figure showing a map of the Carribean Sea and its surrounding water bodies and land masses with purple, green, and red pin drops indicating locations of various <i>Diadema</i> reports.
Map of Diadema antillarum tracking in Florida and the greater Caribbean. Source: AGRRA. 2022. Diadema Response Network - Map of Diadema and other sea urchins in the Caribbean. ArcGIS Online. [May 10, 2022].

NCRMP will contribute to monitoring the current Diadema mortality event by adding a visual assessment of Diadema antillarum health condition to the current monitoring protocol. This work will occur along the Florida Reef Tract and Flower Garden Banks (Gulf of Mexico) during the 2022 field season. If divers observe Diadema antillarum, they will note whether individual urchins are healthy, diseased, or dead. NCRMP field surveyors will report disease observations immediately to partners and colleagues at the Atlantic and Gulf Rapid Reef Assessment, which has developed a Diadema Response Network to track Diadema health as well as coordinate information sharing, data collection, and research.

For more information about NCRMP, contact Erica Towle.

For more information or if you want to become involved in the Diadema Response Network, contact

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