The vibrant coral reefs of the Red Sea are an underwater paradise that are home to a wide variety of fascinating marine life as well as stunningly beautiful fish.
These reefs have demonstrated remarkable resistance to warming sea temperatures despite the effects of climate change.
However, a new threat has emerged due to the mysterious extinction of a significant species of sea urchins, raising concerns that this valuable habitat will become more and more overrun by rapidly expanding green algae.
There could be catastrophic effects on tourism.
Near the southern city of Eilat, black sea urchin deaths were first noted by Israeli researchers at the beginning of the year.
The 50 cm long defensive spines on the spiky creatures are well known to scuba divers and snorkelers who frequent the Gulf of Aqaba for its crystal-clear waters. They once covered some of the area's coastal reefs.
According to recent surveys, a waterborne parasite is thought to be responsible for the 90% decline in the Jordanian resort of Aqaba, mass disappearances in Egypt, and losses in Saudi Arabia.
Dr. Omri Bronstein of Tel Aviv University hands me a dead black sea urchin with a body the size and shape of a tennis ball and says, "We know the pathogen hurts.
He claims there are outward indications that the sea urchins' spines and tiny feet are paralyzed by the illness.
"You observe what we refer to as necrosis, where tissue is lost until a bare skeleton is left. Additionally, they die very quickly; the entire process lasts about 48 hours. ".
Scuba diver videos demonstrate how predatory fish quickly consume infected black sea urchins without their protective spines.
Fish and human activities, particularly shipping, appear to have contributed to the spread of the disease.
One of the world's oldest continuously surviving reefs, the Red Sea's, which is thought to be over 5,000 years old, may experience significant ecological effects.
The sea urchins are essential for the growth and settlement of coral larvae as well as for preventing algae from encroaching and obstructing sunlight by eating it.
Omri Omessi, an Eilat-based maritime inspector for the Israel Parks and Nature Authority, says that corals and sea algae are constantly vying for space.
Once the urchins are gone, he claims that sea algae will spread much more quickly: "Sea algae can spread way faster than corals. We are aware that corals can expand an average of 1 cm per year. In a single day, sea algae can grow 1 cm.
He shares a personal story about going on a diving vacation in Nuweiba, Egypt, which is about 80 kilometers (50 miles) to the south after he started tracking the disappearance of black sea urchins in the far north of the Gulf of Aqaba, to demonstrate how quickly the disease has spread.
He recalled thinking "everything may be OK" when he saw thousands of black sea urchins in Egypt.
"However, two weeks later, the locals warned me that I would not see a single one of the street urchins if I returned to Nuweiba. This is incredibly violent. It moves extremely quickly. ".
Dr. Mahmoud Hanafy, a marine biologist at Suez Canal University, has been conducting his own research farther south along the Egyptian Red Sea coast.
He tells me that previously, you could easily find 20 to 30 per sq m (10 point 7 sq ft). "At this point, the black sea urchin has vanished from every region I surveyed, from north of Hurghada to south of Marsa Alam. I was unable to locate any specimens. ".
According to him, this indicates that the species may be going extinct in the area.
Significant die-offs have also occurred nearby in other countries. These include Saudi Arabia, which has checked 113 sites along its extensive coastline, and Jordan, which examined 13 sites. Saudi Arabia, however, has not yet made its findings public.
Following reports of sea urchin deaths close to Muscat in Oman, worries have been expressed that the trend may spread to the Arabian Gulf. Losses off the Somalian coast of the Indian Ocean were also reported to the BBC.
Concerning the potential effects, opinions vary.
Scientists in Egypt and Jordan whom I spoke to emphasize that their reefs do not yet appear to be suffering from the disappearance of the sea urchins. They draw attention to the fact that corals are still supported by other marine life.
Some experts worry that what occurred in the Caribbean 40 years ago, when a pathogen wiped out up to 99 percent of a closely related species of sea urchin, will happen again. An active coral reef was transformed into an algal swarm.
They claim that until the winter, when algae naturally blooms, the effects in the Red Sea may not be obvious.
In Dr. Bronstein's lab in Tel Aviv, the hunt for the exact cause of the black sea urchin deaths is on. Studying environmental DNA, which they by chance were already collecting from the waters off Eilat at the time the pathogen first appeared, is one method they are employing.
Because it truly is the "black box" of this event, it is already regarded as a treasure. We only need to decipher it now, says Dr. Bronstein.
There are additional signs of optimism.
The Tel Aviv team has been researching black sea urchins in the Eastern Mediterranean for about ten years now, ever since they were introduced as an invasive species from the Red Sea.
Although the recent die-offs were first to affect these populations, which are generally considered pests, there are still some healthy pockets that could be kept as a broodstock and eventually released back into their natural habitat.
In the Gulf of Aqaba, a few newly emerged young urchins are also being watched.
Dr. Bronstein sees encouraging cooperation in this politically complex region, where Saudi Arabia and Israel do not have formal ties, while individual nations are acting to combat overfishing and pollution, which each pose a risk to coral reefs.
Under water, according to Dr. Bronstein, "the distances between Israel, Jordan, Egypt, and further south don't really exist.".
Even though the cooperation is frequently kept private, he claims that countries are cooperating better and sharing information.
Although there are many differences between the nations that share the Red Sea's turquoise waters, the fate of the black sea urchin demonstrates their shared desire to protect the marine environment.
