Great news for coral reef restoration: First diadema sea urchins cultured on Saba

On October 22st, 2021, the first ever recorded Diadema sea urchins in the Caribbean were cultured on Saba. Diadema sea urchins are important grazers and can facilitate corals by reducing their competition with algae. By culturing them, researchers from University of Applied Sciences Van Hall Larenstein set an important step in restocking sea urchins on Saba’s coral reefs.

First juvenile Diadema sea urchin cultured in the Caribbean within the process of metamorphosis. Squares are 1×1 mm.

The long-spined black sea urchin, also known as Diadema, has been absent on most coral reefs throughout the Caribbean since 99% of all populations died of an unknown disease in the early 80s. Before the die-off, these sea urchins were the major herbivore in the Caribbean, by scraping off and eating the seaweeds. After the mass mortality, Diadema sea urchin populations never really recovered and most reefs nowadays are dominated by macroalgae. Restoring Diadema populations is therefore seen as a key priority in Caribbean coral reef management.

Culturing Diadema and releasing them in the wild would speed up the recovery of this keystone species. Unfortunately, the culture of Diadema is very hard, due to the sensitive nature of the larvae. It has been tried several times, especially in Florida, but despite some successes, a consistent method was never developed. In 2020 a new culture method was developed in The Netherlands by researchers from the University of Applied Sciences Van Hall Larenstein, making it possible to consistently culture Diadema from tiny larvae to juvenile sea urchins.

First 19 cultured Diadema sea urchins in the Caribbean. Squares are 1×1 mm.

In July of this year, the research team moved their culture efforts from the cold and not so tropical Netherlands to Saba, in an attempt to culture juveniles near the reefs where they are much needed. With help of the Saba Conservation Foundation (SCF), the first larvae have successfully been cultured and settled, resulting in the first 19 Caribbean cultured Diadema sea urchin juveniles. The first 19 cultured Diadema are raised in captivity until they are big enough for release in the wild, where they can graze away the algae that are smothering the corals and prevent new corals from settling.

The next step is to upscale cultivation, with currently over 3,000 larvae being cultured. If this approach is proven to be effective on Saba, it can be copied throughout the Caribbean. By removing their most important competitors, Diadema sea urchins can help coral reefs to cope with other stressors like climate change and pollution.

More information:

Or contact researchers Tom Wijers ( or Alwin Hylkema (

Alwin Hylkema

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One comment

  1. Per this article released in 1984, , a research team led by a Smithsonian biologist, Harilaos A. Lessios, found that an yet unidentified water-borne pathogen attacked the black sea urchin, Diadema antillarum, but left six other species of sea urchin unharmed. Since the water-borne pathogen couldn’t be identified at the time and the waters may not be free of this pathogen at the time of release of the new cultured species into the underwater environment, could history repeat itself? Maybe this new culturing method developed in The Netherlands by researchers from the University of Applied Sciences Van Hall Larenstein could naturally breed a stronger class of black sea urchins with traits of the other non-affected sea urchin species to help build up the immune system of the new cultured generation of black sea urchins. Could this help reduce the risks of exposure to similar water-borne pathogen conditions that could repeat history? Maybe this article released 1 month ago lead to some answers? Food for Thought….

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