A deadly plague wiped out all the black sea urchins in the Gulf of Eilat within a few months and threatens to collapse the coral reef
A new and alarming series of studies by Tel Aviv University reveals a deadly trend that is causing mass mortality of black sea urchins in the Mediterranean Sea and the Gulf of Eilat. The real danger: without the urchins that serve as the 'gardeners of the reef', the algae will take over and suffocate the corals, who will no longer be able to enjoy the sunlight. The findings indicate that within a short period of time the population of black sea urchins was completely wiped out from Eilat. For example, within a few months, thousands of sea urchins died that lived at the site located on the northern shore of the Gulf of Eilat. The trend is so severe that at this site and at other sites in the bay, only urchin skeletons remain. This is also happening in other countries in the region, including Jordan, Egypt, Saudi Arabia, Greece and Turkey.
A pathogenic parasite from the Mediterranean threatens Red Sea urchin populations
The research was conducted under the leadership of Dr. Omri Bronstein and doctoral students Rotem Zirler, Lisa Maria-Schmidt, Lahan Roth, and Gal Avitar from the School of Zoology and the Steinhardt Museum of Nature at Tel Aviv University. The studies were published in the journal Frontiers in Marine Science and Royal Society Open Science.
The researchers emphasize that sea urchins in general, and the long-spined herring in particular, are considered key species that are essential for the healthy functioning of the coral reef. "You have to understand that the level of threats to coral reefs is still at an all-time high, and now a new variable has been added that we don't know about. There was no such situation in the recorded history of the Gulf of Eilat," says the team of researchers sadly.
The researchers estimate that the source of the deadly plague is a single-celled pathogenic parasite from the ciliate family that moved from the Mediterranean Sea to the Red Sea. Following the research, a report was submitted to the Nature and Parks Authority reviewing the current situation, and these days the emergency measures to be taken to save Israel's coral reef are being considered.
"Due to the intensity of the death rate, we first thought it was pollution, a local chemical spill, or poisoning from industry and hotels in the northern Gulf, but after checking other sites in Eilat, Jordan, and Sinai, we realized that this was not a local event," explains Dr. Bronstein and continues, "All the signs point to an epidemic that is spreading Faster. Similar reports also come from colleagues in Saudi Arabia. Even urchins that we raised in aquariums for research purposes at the Inter-University Institute, and the sea urchins at the underwater observatory in Eilat, became infected and died, apparently because the pathogen managed to enter through the pumping systems."
According to Dr. Bronstein, this is a quick and violent death: "Within two days, a healthy hedgehog turns into a tissue-less skeleton." While some of the corpses wash ashore, most of the urchins are devoured while they are dying and unable to defend themselves, which can accelerate infection by the fish that prey on them.'
The danger: the corals are suffocated by algae
In recent years, Dr. Bronstein's research group has been investigating the issue of marine invasions, and among other things, is focusing on a species of sea urchin called Diadema setosum, which in Hebrew is called the long-thorned sea urchin. "Until recently it was one of the most common species in the Eilat coral reef. These are the black hedgehogs with the long spines we all know. Sea urchins in general, and the long-spined sea urchin in particular, are considered keystone species that are essential to the healthy functioning of the coral reef. The urchins are the 'gardeners' of the reef - they feed on the algae and prevent them from taking over and suffocating the corals that compete with them for sunlight. "Unfortunately, these urchins no longer exist in the Gulf of Eilat, and further south from there in ever-expanding parts of the Red Sea," says Dr. Bronstein sadly.
The first reports of mass deaths reached Dr. Bronstein a few months ago from his colleagues in Greece and Turkey, where the hedgehogs invaded - probably through the Suez Canal. "In 2006, the first urchin of this species in the Mediterranean Sea was found in southern Turkey. This is a phenomenon that we recognize as a biological invasion, with extensive ecological consequences, which is very common in the eastern Mediterranean and especially along Israel's coastline, "since then we have been following the dynamics of the species' invasion in the Mediterranean," he says.
In 2016, they discovered the first sea urchin on the shores of Israel - a single individual on Gordon Beach in Tel Aviv. According to him, for more than a decade since the first discovery in Turkey, the populations in the Mediterranean Sea remained small and mostly hidden, but as of 2018, the urchins in the Mediterranean Sea reached a state of exponential growth or population explosion - and in Greece and Turkey huge populations of thousands and tens of thousands of individuals were observed.
"But while we were working on a study summarizing the invasion of sea urchins in the Mediterranean, we began to receive reports of sudden and widespread mortality. Apparently, there is nothing wrong with the extinction of an invasive species in the Mediterranean, but two important points must be remembered: first, we do not yet know how mortality and its causes will affect native species in the Mediterranean. Second, and worse, the geographical proximity between the eastern Mediterranean and the Red Sea may allow the pathogen to quickly pass to the natural population in the Red Sea, which unfortunately did happen."
"The algae multiplied without control, they hid the sunlight from the corals and the entire reef underwent an irreversible change - from a coral reef to fields of algae"
The same sad story elsewhere in the world
The mass mortality reminded researchers from Tel Aviv University of one of the most well-known and serious stories in the history of marine ecology: the story of the disappearance of sea urchins from the Caribbean. Until 1983, the coral reef in the Caribbean was a thriving tropical reef that closely resembled the coral reef in the Gulf of Eilat. But then a mysterious disease wipes out most of the population of sea urchins of the species Diadema antillarum - relatives of the sea urchins from Eilat. When the urchins disappeared, the algae multiplied uncontrollably, hiding the sunlight from the corals and the entire reef underwent an irreversible change - from a coral reef to fields of algae."
"Last year, the disease returned and broke out in the Caribbean, killing the surviving populations and individuals," says Dr. Bronstein. "Unlike the events of the past, today we have the scientific and technological tools to decipher the forensic evidence. A group of researchers from Cornell University last month identified the cause of death in the Caribbean: a pathogenic parasite from the ciliate family. The pathology we detect in the sea urchins that die in Greece and Turkey is the same as the pathology of the urchins in the Caribbean, and this is also the pathology of the urchins that die here in the Red Sea."
Dr. Bronstein's research is the first to indicate mass mortality of an invasive species in the Mediterranean, and the first to indicate mass mortality among sea urchins of the species Diadema setosum - one of the most common sea urchin species in the world. Dr. Bronstein concluded his groundbreaking research with a warning that the plague that is currently breaking out in the Mediterranean Sea may also spread to the nearby Red Sea, a warning that, as mentioned, came true.
"You have to understand the seriousness of the situation: mortality in the Red Sea is progressing at breakneck speed, and the affected areas already encompass a much wider area than we know in the Mediterranean Sea. In the background there is still a big mystery: what kills the hedgehogs? Is this the Caribbean pathogen or a new and unknown cause? Either way, it is clear to us that the pathogen is carried in the water, and we predict that in a short time the entire population of these urchins, both in the Mediterranean and the Red Sea, will get sick and die."
"The window of opportunity to preserve a healthy population of this species in Eilat has already closed. We must act today to establish a breeding nucleus and preserve healthy individuals from the Israeli Mediterranean Sea, before the disease reaches there as well."
In Dr. Bronstein's opinion, a breeding nucleus of these sea urchins should be established today, so that if necessary they can be returned to the wild in the future. "As with the corona virus, no one knows at this stage what will happen - will this epidemic pass by itself? Or will it remain here for many more years and lead to a dramatic change in the coral reef? It's just that unlike Corona, we don't have the option to vaccinate the hedgehogs or treat them, so we have to invest all our efforts in prevention. Unfortunately, the window of opportunity to preserve a healthy population of this species in Eilat has already closed. If we want to establish a breeding nucleus, we must act today and preserve healthy individuals from the Israeli Mediterranean - before the disease that advances from the north reaches there as well. This is a complex task, since the pathogen is carried in water and we will have to establish a cultivation system that is completely disconnected from the sea, but this is a necessary step if we want to ensure the survival of this unique and critical species for the future of the coral reef."
