In the Water: Echinoderms

Atlantic long-spined sea urchin

Diadema antillarum

Jumplinks:

About

This sea urchin thrives in the warm, tropical waters of the Atlantic, and is found all over the Caribbean. Their bodies can grow to be 8–10 cm/3–4 inches in diameter, and their primary spines can grow to be up to 30 cm/nearly 1 foot long! Diadema hobbies include (but aren’t limited to): nestling into sneaky ocean crevices, being voracious herbivores, and impressing with their long, stunning spines.

Diadema are critical coral reef residents. They primarily eat algae, and their consistent grazing habits prevent algae from overgrowing corals, maintaining balance in the ecosystem. In the 1980s, these sea urchins faced a massive mortality event caused by an unknown disease, and as a result, many Caribbean reefs are still struggling today to restore that balance.

Despite the odds, though, hope remains for these important reef residents. Some studies have found that Diadema are slowly returning to coral reefs, and while there was another die-off in early 2022, scientists were able to identify the pathogen causing it within the year, thanks in large part to the efforts of researchers and communities across the Caribbean who mobilized to report sightings and collect samples.

Today, scientists across the Caribbean — including on Saba! — are raising baby Diadema in labs to study how best to help restore this species in the wild. It’s not an easy process, but it’s well on its way. Through this ongoing research and more, humans can continue to support the comeback of this critical species, a key player in the overall work of making reef ecosystems more resilient. Don’t miss the “Ask a Scientist” module below to learn how you can get a in-person look at local urchin-restoration efforts!

This species is:
Native

Why that matters:
Native species are those that evolved in the region naturally, without human influence. That means they’re specifically adapted to Saba’s habitat, and play a key role in island biodiversity. When we lose native species, gaps appear in the ecosystem. That leads to cascades of additional extinctions, and to the loss of the ecosystem services (food, clean air and water, flood and coastal protections, and more) that we humans rely on.

Credit: @zahnerphoto, iNaturalist (CC-BY-NC).

iNaturalist Observations

Long-spined sea urchin

iNaturalist user @djscho (CC-BY)

iNaturalist user @zahnerphoto (CC-BY-NC)

iNaturalist user @yellobird (CC-BY-NC)

Where locals, researchers, and visitors have seen this species.

Saba Island Map and Pins: iNat Taxonomy ID 52290

This map shows geotagged observations of this species made on iNaturalist, the world’s largest community-science platform.

iNat depends on people like you. By uploading photos of species you see in the wild, you can easily learn more about them — while also contributing critical data used by scientists and conservation-managers around the globe.

See something odd?

Observations of land species in water:
Connectivity can affect how accurate location services are, and in the case of endangered species, location is often automatically obscured.
Missing observations:
Your help is needed to collect more data for this species!

Ask a Scientist

Question: How would you summarize your work on Saba thus far?

Answer: We’ve been able to develop multiple intervention methods that have proved successful on a smaller scale — we add small structures on the reef where sea urchin larvae can actually settle, and we’ve developed a new method by culturing them on shaker tables to keep the larvae healthy. But there are a lot of reefs here on Saba, and especially in the Caribbean, so now we need to upscale our technology to begin to actually make a measurable impact. Feel free to come by anytime and you can see it yourself! We’re next to the Saba Conservation Foundation.

Alwin Hylkema
Aquaculture & fisheries researcher at Van Hall Larenstein University of Applied Sciences, has been working on Saba since 2019.