A marine pandemic is bringing some species of sea urchin to the brink of extinction, and some populations have disappeared altogether, a study has found.

Since 2021, Diadema africanum urchins in the Canary Island archipelago have almost entirely been killed by an unknown disease. There has been a 99.7% population decrease in Tenerife, and a 90% decrease off the islands of the Madeira archipelago.

In the same period, mass deaths have been detected in species from the Red Sea, Mediterranean, Caribbean and western Indian Ocean.

Iván Cano, a researcher at the University of La Laguna and author of the study, said: “What we have seen since 2021 is really, really concerning. We are talking about the disappearance of several species in a really short time.”

Sea urchins are remarkable creatures. A relative of the starfish, they breathe through their feet, and while their spikes are a formidable defence against predators, they also provide refuge for smaller marine creatures.

They are known as “ecosystem engineers”, and affect their surroundings by grazing on algae, breaking down food for other animals, and acting as food for predators.

By controlling algal growth they promote the survival of hard coral, itself the habitat for thousands of marine species. Their loss has been felt in Caribbean reefs, where coral cover has halved and algal cover increased by 85%.

“What fascinated me in the first place about this species is that they change their environment. Like humans, when they are present, they modify their habitat,” said Cano. “We don’t know the cascading effect that this could have in other species.”

The scientists do not know exactly what has caused this pandemic, but Cano said humans were “probably involved” in the distribution of the disease. Current theories about its transmission include shipping, changes to currents and abnormal wave activity.

Cano came to the Canary Islands to study the early life of urchins. He quickly found, to his dismay, that there were not enough young urchins to study. As a result, he changed his doctoral subject to study the rapid decline in their populations.

The Diadema genus, which populates tropical waters around the world, are the most widespread and ecologically important family of urchin.

There are only a few pockets of water where Diadema have not been affected by this outbreak of disease.

“We aren’t yet sure how this pandemic will evolve,” Cano said. “So far, it seems not to have spread to other populations in Southeast Asia and Australia, which is good news – but we cannot rule out the possibility that the disease will reappear and potentially spread further.”