The deadly parasite that destroyed sea urchins in Eilat has also spread to the Indian Ocean
A follow-up study by an international team of researchers, led by researchers from Tel Aviv University, has identified that the pathogen responsible for the deaths of sea urchins on the shores of the Red Sea and sea urchins off the coast of the French island of Réunion in the Indian Ocean is now spreading to the Pacific Ocean. The researchers warn that this is an extremely violent global pandemic and are now leading an international effort to chart the course of the disease and conserve the urchins, which play a crucial role in the life of coral reefs.
The study was conducted under the leadership of Dr. Omri Bronstein, from the School of Zoology in the George S. Wise Faculty of Life Sciences and the Steinhardt Museum of NatureThe disturbing discovery was published in the prestigious journal Ecology.
Sea urchins are in danger of disappearing.
"This is an ecological disaster of the first order," explains Dr. Bronstein. "Sea urchins are essential to the health of the coral reef. They are the 'gardeners' of the reef - feeding on algae and preventing them from taking over and 'suffocating' the corals that compete with them for sunlight. In 1983, a mysterious disease wiped out most of the Diadema sea urchins in the Caribbean. The algae there multiplied unchecked, blocking the corals from sunlight, and the entire area underwent a transformation from a coral reef to an algae field. Although 40 years have passed, the sea urchin population - and with it the reef - has not returned to its previous state."
In 2022, the disease reemerged in the Caribbean, affecting populations and individuals that survived. This time, researchers had the scientific and technological tools to collect and interpret the forensic evidence, and researchers from Cornell University successfully identified the fatal pathogen: a scuticociliate parasite. A year later, in early 2023, Dr. Bronstein was the first to identify mass mortality events of long-spined sea urchins—a relative of the Caribbean sea urchin—in the Red Sea.
"Until recently, this was one of the most common urchins on the coral reef in Eilat. These are the black urchins with the long spines that we all know," says Dr. Bronstein. "Today, this sea urchin is almost no longer present in significant numbers in the Red Sea. This is an extremely violent event: in less than 48 hours, a healthy population of sea urchins turns into decaying skeletons. At certain sites in Eilat and Sinai, mortality rates reached 100%. In further research, we were able to show that the Caribbean pathogen is in fact the same pathogen that attacked the populations in the Red Sea."
Now, using genetic tools, Dr. Bronstein and his colleagues overseas have shown that the Caribbean and Red Sea rassin is also behind similar mortality events off the coast of Reunion Island in the Indian Ocean.
"This is actually the first genetic confirmation that it's the same pathogen in all these places," he says. "Now it's a global event, a pandemic. The Red Sea, the Caribbean and the Indian Ocean are key coral reef areas in the world, and the mortality rates of urchins in all these sites are very high, over 90%. We don't yet have evidence of the presence of this pathogen in sea urchins in the Pacific Ocean, and that's definitely something we're working on these days. Although we have developed genetic tools for specific identification of the pathogen, we have to understand that it's difficult to track such rapid extinction events in the underwater environment. We are terrestrial creatures, some of the reefs are deep in the sea and extend over vast areas, and if we miss the mortality event even by two days, there might not be anything there, not even a trace of the extinct population."
No Pfizer and Moderna for sea urchins
To monitor the progress of the epidemic, Dr. Bronstein has established an international network of partners, to whom he provides alerts about the likelihood of a fatal event occurring in their area, and also sends them the equipment needed to sample and preserve the sick hedgehogs in a way that allows comparison with samples from other sites – kits that are sent back to the laboratory at Tel Aviv University.
"A population that is already infected and sick, we really don't have the tools to help them," says Dr. Bronstein sadly. "There is no Pfizer and Moderna for sea urchins. Not because we don't want to, there is no because we can't treat them underwater. Our focus needs to be on two completely different axes. The first is prevention. To prevent the further spread of the epidemic, we need to understand why it broke out here and now. We have developed two hypotheses for this. The first hypothesis is the transport hypothesis: the pathogen from the Caribbean moved with the help of humans to new and distant areas after being sucked into the ballast water of a ship and infecting sea urchins in the Red Sea, before moving on to the eastern Indian Ocean. Incidentally, if this hypothesis is correct, we would expect to see mortality events in West Africa as well, since many cargo ships from the Caribbean stop there on their way to the Mediterranean Sea and from there through the Suez Canal to the Red Sea. And now, in the last few weeks, we have discovered that such widespread mortality has indeed occurred in West Africa, as we expected, and we have even managed to obtain a limited number of samples collected during the deaths, which we are currently analyzing in the laboratory. If ships are indeed the source of distribution, then it will be possible to think about treatment methods. It is not simple, and ships will never be completely sterile, but there is something to be done. The second possibility is even more worrying, because it holds that the pathogen has always been here, and it is climate change that has made it violent and erupting. This is a challenge of a different order of magnitude, and we as marine biologists have few ways to respond to it."
In parallel with the global effort, Dr. Bronstein recently established a breeding nucleus of the affected sea urchins at the Israel Aquarium in Jerusalem in collaboration with the Biblical Zoo and the Israel Nature and Parks Authority, so that they will constitute a reserve for the restoration of the affected populations and enable the advancement of research on the mechanisms of infection and perhaps even possible methods of treatment.
"The pathogen is transmitted through water, so even urchins that we raised for research purposes in the aquariums of the Inter-University Institute, as well as the sea urchins at the Underwater Observatory in Eilat, fell ill and died. Therefore, together with the Israel Aquarium and the Nature and Parks Authority, we established a breeding nucleus at the Biblical Zoo in Jerusalem, whose aquariums are completely cut off from the sea water. We genetically test the urchins that are transferred to the nucleus to ensure that they are not carriers of the disease, and that they genetically belong to the Red Sea population so that we will have the opportunity to rehabilitate the population in the future. At the same time, we are using them to develop sensitive genetic tools for early detection of the disease from seawater samples as well, such as underwater corona tests."
More of the topic in Hayadan:
