Sea urchins die-off in the Indian Ocean

01.12.2023

In early 2022, sea urchins mysteriously died in the Caribbean. Longspined sea urchins (Diadema antillarum) play a crucial role in coral reefs, as they graze on algae that would otherwise suffocate the corals. Back in the 1980s, sea urchins almost completely disappeared during a massive die-off, the cause of which was unknown.

In March 2023, a research team reported a mass die-off of the species Diadema setosum in the Mediterranean Sea. The problem showed similar pathologies as in the Caribbean, which also suggests a pathogenic infection as the cause.

Transport by ships' ballast water, local currents and feeding on infected individuals appear to spread the pathogens at different geographical scales. Due to the proximity of the Mediterranean to the Red Sea, the pathogens were introduced into the native D. setosum population in the Red Sea shortly afterwards - with potentially catastrophic consequences. And now, a few months later, a mass mortality was also discovered in the Indian Ocean and on Zanzibar.

Although sea urchins - especially Diadema and Echinothrix - have a very bad reputation among coastal dwellers, kite surfers and tourists due to their huge populations, their ecological importance is enormous. We have to be really concerned about the possible consequences for the local coral reefs, because the main algae eaters - the herbivores (plant-eating fish) are mercilessly overfished around Zanzibar.

A Sea Urchin Taskforce was immediately set up by marine scientists in the region and they are now trying to find out the extent of the mass extinction. Fortunately, there is already some reliable data on the sea urchin populations. We also recorded the local populations from June to September as part of the SOMWAT Meerwissen research project. Thanks to this data, it will hopefully be possible to make reliable statements about the before and after. An antidote to the pathogenic infections is not yet known.

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