Scientists have discovered why sea urchins are dying at an alarming rate in the Middle East – and poison or pollution are not to blame.
Sea urchins have been killed in mass numbers in an epidemic scientists have warned could threaten the Arabian Gulf's coral reefs, which rely on the creatures to keep algae at bay.
Experts now suspect a tiny parasite could be the culprit.
Concerns were raised that the mass die-offs of long-spined sea urchins would spread to the Arabian Gulf following reported deaths in the Gulf of Oman on reefs near Muscat.
Sea urchins also died in large numbers in a matter of weeks near Eliat in Israel and along Saudi Arabia's Red Sea coast.
Tel Aviv University
Dr Omri Bronstein of Tel Aviv University, who has led the research looking at deaths in the Gulf of Aqaba, at the northern end of the Red Sea, said healthy sea urchins turned skeletal in a couple of days.
“We've never seen anything like the speed at which this is unfolding in terms of severity, intensity and rate of progress of the pathogen,” he told The National.
Prof John Burt, head of the marine biology lab at New York University Abu Dhabi, said that it was suspected that the pathogen had been transported in ship ballast water from the Caribbean, where there have been similar large-scale deaths this year.
Tests carried out by the lab's researchers this week at five coral reef sites around Abu Dhabi did not find evidence of mass die-offs.
However, Prof Burt told The National that there was high risk of death and damage to coral reef, given the high level of shipping activity.
“If this pathogenic species is being transported via shipping, it is likely only a matter of time before we see it on our shores, and further monitoring and plans towards marine management interventions are in order,” he said.
“Given the pace at which it has spread across the Red Sea and into the Gulf of Oman, we anticipate its arrival in the Emirates is imminent.”
One population of long-spined sea urchins at the northernmost tip of the Gulf of Aqaba that Dr Bronstein and his doctoral students recently surveyed was wiped out at extraordinary speed.
“The site that literally had thousands of sea urchins was obliterated over two weeks,” he said.
The pace of the deaths was such that Dr Bronstein and his team first thought that pollution or poisoning was to blame.
“When we started extending our surveys to Jordan and Egypt, we realised we’re not looking at a local pollution event, rather something rapidly extending,” he said.
One of the factors behind the quick spread of the disease is the very narrow topography of the Gulf of Aqaba and the Gulf of Suez, as well as the entire Red Sea, Dr Bronstein said.
“The ocean has no borders,” he said. “If the disease is waterborne, it will reach all places. This is not something we should tackle independently.”
Dr Bronstein has been examining the deaths of long-spined sea urchins and working with colleagues in Jordan, Egypt and eastern Mediterranean nations, where the species is regarded as invasive.
Dr Mahmoud Hanafy, professor of marine environment studies at Suez Canal University in Cairo, said he conducted a sweep of black sea urchins and had not seen a single one.
“It's really quite strange,” he said.
professor of marine environment studies at Suez Canal University in Cairo
Dr Hanafy said fishermen in South Sinai had confirmed that sea urchins started dying en masse there about two months ago.
However, despite remaining optimistic that the mass disappearance will not have catastrophic effects, the reality says otherwise.
“It's an essential species for the stability of the ecosystem because it regularly feeds on algae and prevents it from growing uncontrollably on the corals to the point where it kills them. But it's important to note that there are other species that do the same thing,” he said.
Dr Hanafy cautioned against drawing hasty conclusions but stressed the importance of further research at a regional level.
“That said, the speed and profuseness with which the parasite has killed entire colonies of sea urchins across thousands of kilometres is really quite strange,” he said.
“But I think that if the root causes of the problem are dealt with quickly enough, the reefs could very well recover.”
The pathogen is thought to have spread from these Mediterranean populations to the Gulf of Aqaba.
When infected, the sea urchins become paralysed, leaving them helpless against predatory fish.
Tests being carried out in the coming days are expected to identify the parasite, which is thought to be a single-cell pathogen with the scientific name Philaster apodigitiformis.
The first reports were from the US Virgin Islands in the Caribbean while deaths were reported off Jamaica and Florida earlier this year.
In the 1980s, there were mass deaths among sea urchins in the Caribbean, resulting in damage to coral reefs.
These have yet to recover from the devastation, Dr Bronstein said, offering a “scary” vision of what could happen to reefs – already under pressure due to climate change – hit by the latest epidemic.
Long-spined Diadema sea urchins have been described as the “gardener” because they prevent algae from overwhelming reefs.
“They feed on the algae that compete with corals for sunlight. The coral growth rate is nothing compared with the algal growth rate,” Dr Bronstein said.
“The algae will always out-compete the corals [which] need the herbivores.”
He said populations of Diadema setosum in the eastern Mediterranean, the Red Sea, the Arabian Gulf and neighbouring areas were distinct from those elsewhere in the world.
The die-offs could wipe out this unique type, described by scientists as Clade B, and populations of D. setosum from elsewhere may not be able to repopulate areas in the Middle East.
Dr Bronstein would like to establish a “brood stock” of Clade B sea urchins for such repopulation efforts in the future.
“If [the parasite] will reach all the way through the Red Sea, it will reach the [Arabian] Gulf and we’re looking at a threat of losing the entire genetic clade, which is adapted to living in our environment,” he said.
“It’s something we must work quickly to try to mitigate,” he said. “We have a narrow window of opportunity to actually do something.”
The plan is to use uninfected populations in the Mediterranean to establish this brood stock.
