Mass death of sea urchins threatens Red Sea reefs

The rainbow-hued coral reefs of the Red Sea are teeming with vibrant fish and an array of soft and hard corals that attract divers from around the world. But now, these reefs are threatened by the death of sea urchins that protect the reefs from overgrowth of algae.

Since spring 2023, there has been a mass die-off of Diadema sea urchins in the Mediterranean and northern Red Sea. These ecologically important sea urchins are vital for the health of coral reefs, and if lost, can have dramatic consequences for reef ecosystems.

Aquatil, an environmental research and education non-profit, are taking action to report the disappearance of diadem sea urchins and they need your help. Read on to find out how you can support their Dive4Diadema Citizen Science project.

What are Diadema sea urchins and why do they matter?

Diademais a widespread and ecologically important group of tropical sea urchins made up of nine species.One of these sea urchin species, Diadema setosum (Leske, 1778), entered the Mediterranean Sea through the Suez Canal in 2006 and is currently an established non-native species frequently seen by divers.

The original range of this sea urchin species extends from the central Pacific to the East African coast, including the Red Sea. As grazers, these sea urchins create space for larvae to settle and prevent the spread of algae that can displace slower-growing organisms such as corals. As such, they play a vital role in ensuring the health of coral reef ecosystems.

Keen to learn more about different marine life and how ocean ecosystems function? Then check out SSI’s Environment Specialty programs.

The mysterious loss of Diademasea urchins

In the early 1980s and 2022, there was a mass die-off of Diadema antillarum in the Caribbean caused by a pathogen. This led to dramatic changes in the coral reefs, which became overgrown with algae.

In 2009, 65% of all Diadema africanumsea urchins died on the African east coast, and in 2018, 93% died in the Canary Islands. Now, in the spring of 2023, a mass die-off of Diadema setosum has also started in the Mediterranean and within a short time has continued into the northern Red Sea.

Concerns have been raised that if this latest die-off continues, the affected coral reefs could become choked with green algae.

How you can help - Dive4Diadema

Aquatil are currently working on a Citizen Science project Dive4Diadema to report the loss of these sea urchins and they need your involvement. They are making a website and a free app for scuba divers to report observations of Diadema sea urchins when they go diving in the Red Sea and diving in the Mediterranean.

It is hoped that Dive4Diadema will become a project for the entire diving community to record the disappearance of Diadema setosum and document the last occurrences. All observations can be sent anonymously or registered with the free app (Android & IOS), which is due to be launched at the end of September. So, grab your dive gear and get involved!

Related: How Soft Sediment Seabeds Can Help Fight Climate Change.

Aquatil is also welcoming financial support to help drive this important project forward. All supporters will be displayed with their logo on the Dive4Diadema project website. If you would like to make a financial contribution, please reach out to the Aquatil team directly at or

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