In search of the last sea urchins

September 21, 2023

The Citizen Science Project Dive4Diadema begins in the Red Sea under the leadership of researchers from the University of Stuttgart
[Picture: Paul Munzinger]

Sea urchins are one of the most important groups of animals in the coral reefs of the Red Sea. They feed on algae and are therefore also the "lawnmowers" of the reefs. Until recently, up to 30 sea urchins of the species Diadema setosum could be found per square meter in the Red Sea. Due to a mass extinction event, the crepuscular and nocturnal animals have now almost completely disappeared. That's why researchers from the Biodiversity and Scientific Diving Research Unit at the University of Stuttgart are launching the Citizen Science Project Dive4Diadema. Thus beginning the search for the last of the diadem sea urchins in the Red Sea.

The Citizen Science approach means that additional scientific knowledge is gathered by people who are not full-time scientists. "With this approach, we hope to learn as much as possible about the spread of sea urchin disease. Diadema setosum appears to have almost completely disappeared along the northern coast of the Red Sea," explains Prof. Franz Brümmer, from the Institute of Biomaterials and Biomolecular Systems at the University of Stuttgart.

"We are trying to find diadem sea urchin populations in the Red Sea that are unaffected or even resistant to the disease causing the mass extinction," adds his colleague Prof. Ralph Schill, from the Institute of Biomaterials and Biomolecular Systems. 

To feed, diadem sea urchins crawl out onto algae-covered surfaces at night, while during the day they sit motionless in hiding places or form clusters on open surfaces

Supported by an app and a diving pioneer

Franz Brümmer and Ralph Schill will be accompanied by the Scientific Diving Center University of Stuttgart (WiTUS). Together with a total of 47 diving centers, diving tour operators, diving training organizations and many non-governmental organizations active in environmental and marine protection, the Dive4Diadema project is now searching for the last of this sea urchin species as a Citizen Science project. Using the new free and multilingual app for iPhone, iPad and Android smartphones, recreational divers can enter their observations from the Mediterranean and Red Sea.

The project is also supported by the renowned diving pioneer and well-known behavioral biologist Prof. Hans Fricke, who already studied Diadema setosum and their behavior in the Red Sea in the 1970s. The Marine Science Station (MSS) from the University of Jordan is also involved. Various cooperation projects on coral reef ecology and scientific diving are also planned, in cooperation with Prof. Ali Al-Sawalmih, the director of the station.

Dramatic changes to biological diversity

Repeated mass extinction events­ have also been experienced with the Caribbean species Diadema antillarum. In the early 1980s, 98 percent of all diadem sea urchins disappeared in the Caribbean. The few that survived have slowly recovered in recent years, but in 2022, a further mass extinction event killed approximately 95 percent of all sea urchins. The disappearance led to dramatic changes in coral reefs and overall underwater biodiversity in the respective regions. Over a short period of time, the colorful and species-rich coral reefs were transformed into a reef landscape overgrown with algae and home to much less varied species populations. This is because sea urchins fulfill an important function in the sea: They contain the spread of algae and thus create space for the settlement of larvae and slower-growing organisms, such as corals, mussels, and bryozoans. Grazing the algae also causes significant bioerosion of the subsoil.

Until recently, up to 30 animals per square meter of the crepuscular and nocturnal species Diadema setosum could be found in the Red Sea, and they have also migrated to the Mediterranean as a non-native species in recent years. Last year, dead sea urchins were observed for the first time in Greece. Since then, these individual deaths have turned into a mass extinction event, which, like the exodus of the diadem sea urchins from the Red Sea via the Suez Canal into the Mediterranean Sea, is now spreading at great speed in the opposite direction into the Red Sea.


Expert Contact:

Prof. Franz Brümmer, Scientific Diving Group from the University of Stuttgart (WiTUS) Institute of Biomaterials and Biomolecular Systems at the University of Stuttgart, Tel. +49 711 685 65083, email:

Ralph-Walter Müller, Scientific Diving Center University of Stuttgart, Tel. +49 711 685 66473, E-Mail:

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