'Like you're on the moon': the strange microbial mats of Abu Dhabi's sabkha flats
Scientists are challenging received wisdom about the reason polygonal, leathery microbial structures form off the coast of the capital
When he stands in the sabkha coastal flats off Abu Dhabi and gazes at the microbial mats that lie in all directions, Stephen Lokier could be surveying a scene from billions of years ago.
He is surrounded by polygon-shaped mounds of micro-organisms, structures known as stromatolites, looking just as they would have done when our planet was little more than half as old as it is now.
“When you go out there, it's like nowhere else on Earth,” said Dr Lokier, an associate professor at the Petroleum Institute Abu Dhabi, part of Khalifa University of Science and Technology.
“Standing on the microbial mats offers exactly the same view it would have standing on the sea shore a couple of billion years ago. It's microbes becoming stromatolites; the same type of structure we see today.”
Turn the clock back two billion years and life on Earth consisted of nothing more sophisticated than micro-organisms, allowing these tiny creatures to form vast aggregations without being eaten by grazing herbivores.
Today, when there are myriad tiny animals to feast on them, other-worldly microbial mats like those found off the UAE coast can only survive in a few localised areas.
“Nowadays, these microbial mats get wiped out – they're incredibly tasty. Any organism can graze on this. They're hanging on in a few places in the world where it's incredibly stressful for other organisms,” said Dr Lokier, a UAE resident since 2002 who has made hundreds of visits to the sabkha.
In the 21st century there has been renewed interest from scientists in researching the UAE's coastal environments. It represents a renaissance in activity after intensive research was carried out in the 1960s, sparked by the growth of the oil industry at the time.
And there can be few more fascinating natural environments to study.
Dr Lokier describes the mats as “rather leathery” when they are walked on, something that is easy to do as they can support the weight of an average person without breaking.
These microbial mats survive in a narrow coastal band – about 200 metres wide – where they are covered during high tides meaning they do not dry out completely and become worn away. They are protected from grazing creatures because they are exposed much of the time and so the creatures face heat stress. The mast, in turn, protect the coastline.
“We definitely think of the sabkha as an extreme environment because of the amount of sun, how it's exposed,” said Dr Angela Sherry, a faculty research fellow in geomicrobiology at the University of Newcastle in the United Kingdom who has carried out research on the sabkha.
“It's a fascinating environment, like nothing I've seen before. You feel like you're on the moon, on some unfamiliar landscape.”
Until now, it had been thought that the microbes formed their distinctive polygonal shapes – a polygon is a shape made of at least three, and usually more, straight sides – as a result of shrinkage caused by drying out, just as cracks might form in mud when a puddle dries out.
However, Dr Lokier and a team of fellow researchers have recently published a paper that takes issue with this suggestion.
“There's always been this assumption and it’s never been challenged, that it’s a shrinkage model that opens up cracks,” said Dr Lokier.
“It’s beginning to get annoying; you cannot have shrinkage in a system that floods with water every day. The whole area gets wet.”
In the paper, published in the journal The Depositional Record, Dr Lokier, Dr Sherry and six fellow researchers at the Petroleum Institute and the University of Newcastle describe an alternative model for what causes the microbes to form the plate-like, pancake-sized polygonal structures on their surface.
Their belief is that high rates of microbial growth are the cause, with material splitting off at the surface to create the plates. Dr Lokier has measured plates that are more than 80 centimetres in diameter, although most are much less than this.
“What is happening is they’re growing upwards and outwards at such a rate they’re running out of space effectively. They’re having to turn over themselves,” he said.
There is a mathematical reason why they tend to form as polygons – pentagons are the most common shape – rather than, say, circles.
“There have been some incredibly complex mathematics on why polygons form. They’re the [best] solution to a problem of space,” said Dr Lokier, adding that similar shapes are seen, on a much larger scale, in a map of the plates that cover the Earth.
“You see polygons at all different scales … I’ve seen some polygons on Mars. They’ve been described on several planets in the solar system.”
The disks can easily be picked up by a person and, remarkably, if one is removed, a new one will have formed in its place within weeks or days.
Three of the other authors of the paper are, like Dr Lokier, geologists based at the Department of Geosciences at the Petroleum Institute. The four remaining co-authors are microbiologists from the School of Engineering and Geosciences at Newcastle University in the United Kingdom.
Back in the 1960s, when little seaside development had taken place, the microbial mats were found along about 150km of the UAE coastline. Today about 54km remains, most of it off the coast of Abu Dhabi emirate. The concentration of sabkha reduces significantly between Abu Dhabi and Dubai, although isolated sections remain all the way up to Ras Al Khaimah.
Despite much of it having been lost, there is hope that much of what remains is likely to be protected, at least for the foreseeable future. Dr Lokier says the fact that the mats exist within areas designated as oilfields means they are unlikely to face development pressures for the moment.
Given how other-worldly this habitat is, and that it offers a glimpse into the history of our planet, no doubt many people will be hoping that it continues to exist for a long time to come – perhaps even a few more billion years.
Published: February 17, 2018 03:31 PM