The (only) good news is that the epidemic is not raging among people, but on the seabed. There, the not yet officially identified pathogen preys on sea urchins. And those sea urchins seem completely defenseless; even the healthiest specimens are stripped of all their tissues by the pathogen in two days, leaving only a dead carcass.
At the moment, the epidemic is striking mercilessly in the Mediterranean, researchers write a new study. There lay sea urchins belonging to the species Bristle diadem en masse the lead. “It’s a quick and violent death,” said researcher Omri Bronstein. “Within two days, a healthy sea urchin turns into a skeleton that has lost an enormous amount of tissue.”
Problems in the Mediterranean
In fact, Bronstein and colleagues had no intention of describing a violent epidemic at all. Instead, they researched in the eastern Mediterranean Bristle diadem, a species of sea urchin that has recently managed to penetrate the Mediterranean from its original habitat – the Red Sea. There, the invasive species didn’t seem to do very well at first; after it was first found off the coast of Turkey in 2006, the populations remain small for a long time and only appear sparingly in the Mediterranean Sea. But that will change after 2018. Populations are growing exponentially. In fact, Bronstein and colleagues found sea urchin populations numbering thousands or even tens of thousands off the coast of Greece and Turkey and are scrambling to write a report on the emergence of the invasive species in the Mediterranean region. But the ink is barely dry when they hear the first stories of mass deaths among sea urchins, mainly off the coast of Greece and Turkey.
Worrying
“You could say that the extinction of an invasive species is not a big deal,” says Bronstein. “But it’s good to be aware of two risks. First, we do not know how this mortality and its causative agent affects native species in the Mediterranean. And secondly, and this is even more worrying, the short distance between the eastern part of the Mediterranean and the Red Sea may mean that the pathogen also quickly finds its way to the native populations (D. setosumed.) in the Red Sea.”
Caught up
Bronstein and colleagues also explicitly warn against the latter in their study published last week. But that research has already been overtaken by current events, they must conclude. Because also in the Gulf of Aqaba, an arm of the Red Sea, sea urchins belonging to the species D. setosum now massively dead. For example, the entire population of black sea urchins near Aqaba – the largest city on the Gulf of Aqaba – must now be considered lost; the population has been completely wiped out in a few months.
Epidemic
“At first we thought it was related to pollution or poisoning or local leaching of chemicals from industry or hotels located on the northern part of the Gulf of Aqaba,” Bronstein says. “But we quickly realized that this is not a local incident.” Because sea urchins are also dying in other places in the gulf and even from Jordan, Egypt and Saudi Arabia there are now reports of massive deaths among sea urchins. “Everything points to a rapidly spreading epidemic.” And that epidemic does not only strike wild sea urchins. For example, even sea urchins kept in university aquariums for research purposes have been found to be prey to the disease. “Probably because the pathogen entered through the pump system.”
Implications
The fact that sea urchins are now also falling prey to the pathogen in the Red Sea is very worrying. Because sea urchins in general, but D. setosum in particular, are crucial to the well-being of coral reefs, such as those found in the Red Sea and Gulf of Aqaba, among others. “The sea urchins eat algae,” says Bronstein. And they prevent algae from multiplying uncontrollably and prevent the sunlight that corals need so badly. “Unfortunately, these sea urchins are now no longer found in the Gulf of Aqaba. They are also rapidly disappearing from constantly expanding parts of the Red Sea further south.”
Deadly and fast
Because that’s how fast it goes. “Whatever kills these sea urchins is spreading and it’s spreading fast. And it’s deadly. Even healthy, functioning sea urchins go from a living individual to a dead carcass in 48 hours. And in all areas that are infected, this sea urchin species no longer occurs.”
Parasite
The cause of all this misery is most likely a parasite, the researchers say. Because what is now happening in the eastern Mediterranean – and now also in the Red Sea – strongly reminds scientists of something similar that happened in the Caribbean in the 1980s. There, too, sea urchins died en masse in a short time. And that had major consequences for the coral in which these sea urchins played an important role, says Bronstein. “Once the sea urchins disappeared, the algae could multiply uncontrollably,” says Bronstein. And that happened. “The algae prevented sunlight from reaching the coral and the entire coral was irreversibly transformed – from a coral reef to an algae field.”
Resit
Unfortunately, researchers in the 1980s did not have the resources to identify the pathogen. But last year they got a second chance; the disease struck again in the Caribbean. And this time – with modern technologies – we succeeded in identifying the culprit. It turned out to be a parasite. The clinical picture that researchers are now seeing in the Gulf of Aqaba, but also in the eastern Mediterranean, is identical to the clinical picture in the Caribbean. That is why they are quite sure that the mass death of sea urchins there is also the work of the parasite that has already caused such great damage in the Caribbean.
Serious situation
“We need to understand how serious the situation is,” says Bronstein. He emphasizes again that sea urchins are falling prey to the disease at an astonishingly high rate. And the part of the Red Sea in which the pathogen is already active is much larger than the part of the Mediterranean Sea in which the parasite kills sea urchins. “Meanwhile, there is still a lot we don’t know,” says Bronstein. “What exactly kills sea urchins? Is it the Caribbean pathogen or is something else at play? What we do know is that the pathogen is clearly waterborne and we predict that it will not be long before the entire population of these sea urchins in both the Mediterranean and Red Seas will become ill and will die.”
Intervention is necessary, says Bronstein. But our options are limited. “We do not have vaccinations or treatment methods for the sea urchins, as we did during the COVID-19 epidemic.” Bronstein then sees only one option: save what can be saved. Very concretely, he therefore proposes to start healthy eating as soon as possible D. setosum to fish and secure, so that new populations can be created with it. “If necessary, we can then release the sea urchins back into the wild (…) It will not be easy, but it is absolutely necessary if we want to ensure that this unique species – so important for the future of coral reefs – it survives.”
2023-06-01 17:07:45
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