May 31, 2024 11:01 am
A new disease that can cause the death of entire populations of sea urchins is spreading rapidly in the world’s oceans. The epidemic first appeared in the Caribbean Sea in early 2022, when sea urchins of the species Diadem antillarum they began to die en masse. At first, scientists could not understand the causes of the phenomenon, given that the dead animals had no traces of pathogenic bacteria or viruses.
The culprit later turned out to be a protozoan belonging to the subclass of scuticociliates, unicellular organisms that cause diseases in several types of marine animals but which until now were not known to attack urchins.
In July 2022, large quantities of dead urchins, belonging to a similar species, also began to appear on the coasts of Greece. Diadema setosum. Within a few months the phenomenon spread to other areas of the eastern Mediterranean, reaching the Red Sea at the end of the year and the western Indian Ocean in mid-2023.
Now a study published in Current Biology has confirmed that the pathogen responsible for these latest events is the same one identified in the Caribbean, and that the epidemic has also affected another species, Echinothrix calamaris, suggesting that hedgehogs belonging to different genders may also be at risk. In the Gulf of Aqaba, in the northern Red Sea, both species have disappeared completely.
A collapse in sea urchin populations can have serious repercussions on marine environments. In fact, these herbivorous animals perform an essential function by regulating the presence of algae, whose excessive development can suffocate corals by depriving them of sunlight.
This is what happened after a previous episode of mass mortality Diadem antillarum in the Caribbean Sea in 1983: the disappearance of urchins had caused an uncontrolled growth of algae, which had overwhelmed entire stretches of coral reef. Over the next forty years the ecosystem had never fully recovered. At the time, the causes of the die-off remained unknown, but today scientists suspect that it may have been caused by an organism similar to the one identified in the Red Sea.
The speed with which the epidemic is expanding has amazed researchers, who say its spread may be linked to human activities. The protozoans may have traveled in ships’ ballast water, as have many other invasive marine species. An alternative hypothesis is that these microorganisms were already present in the waters of the affected regions and that they became pathogenic due to environmental changes, for example due to global warming.
At this rate the disease could soon spread throughout the Indian Ocean and reach the Pacific Ocean, threatening Australia’s Great Barrier Reef, already hard hit by bleaching caused by this year’s record temperatures.
According to the authors of the study, a containment strategy could be the analysis of ballast water, but if the uncontrolled spread of the epidemic were to continue the only thing to do would be to collect specimens of the affected sea urchin species as soon as possible to make them survive in captivity and reintroduce them into their environment after the disease has disappeared.
This text is taken from the Pianeta newsletter
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