CORAL CLOSE-UP, FROM A DISTANCE
Local scientist uses satellite images to track the deterioration of corals in the Arabian Gulf,
Satellite images are shining light on the behaviour of Abu Dhabi’s coral reefs.
A study that examined reefs in nine areas of the emirate between 2013 and last year has shown some encouraging results regarding the corals’ ability to survive high water temperatures.
This is a key factor in the survival of Arabian Gulf coral and one that has been studied by scientists over the past decade.
While most earlier studies relied on field observations or genetic studies, Dr Haifa Ben Romdhane is using satellite data to glean information about the health of reefs.
She developed the work as part of her PhD project at the Masdar Institute of Science and Technology and is preparing to publish the results.
Remote sensing is useful for tracking phenomena such as coral bleaching – a negative reaction of corals to heat stress and other adverse factors – in large areas of ocean floor and with high precision, she says.
“Each object on the Earth’s surface, when imaged by satellite-remote sensing, will have its own spectral signature. It is like a fingerprint for us,” says Dr Ben Romdhane.
This is how one can tell the difference between live coral and coral that has bleached, turning white, when looking at satellite images. “Corals are colourful and bleaching would mark the loss of these colours – the microalgae that are living in symbiosis with the coral polyp are expelled and the coral turns white – then the signal that we will get will be definitely different from the response that was obtained from a colourful or live coral,” she says.
In some cases bleached coral can recover, regaining its colour. If the coral polyp dies it is often covered by a different type of algae – macroalgae – turning a greenish colour.
The UAE’s challenging weather presents remote sensing with a challenge. This is why the scientist initially doubted whether the technique would produce results.
“One of the main limits is the transparency of the media that the remote sensing signal is passing through,” says Dr Ben Romdhane.
She says that suspended sand particles in the air, common during sandstorms, or in the water column, deteriorate the signal. Dr Ben Romdhane had to develop techniques to address the attenuation effect of sandstorms and murky water. Eventually she was able to carry out observations from the lab.
The study also relied on data obtained from the water quality monitoring network of the Environment Agency Abu Dhabi, or Ead.
The scientist used the agency’s data and other sources to gather information about parameters such as temperature, light levels, salinity, acidity, dissolved oxygen levels and nutrient enrichment.
She studied these in parallel with satellite images of the reefs to measure how the coral reacted to changes in the environment.
Studying such reactions is important, especially in the Gulf where many corals are living on the temperature tolerance threshold for their species. An increase of a few degrees in water temperature can have a devastating effect.
The El Nino Southern Oscillation, a cyclical periodic shift in the Pacific Ocean that affects weather around the world, for example, killed 90 per cent of Gulf coral between 1996 and 1998.
Dr Ben Romdhane’s study also includes some extreme water temperatures in September 2015. Within that period, however, “there was no major change that altered the corals in any way”, she says.
“The good news is that the tolerance level of UAE corals is higher than other corals around the world and they are more tolerant in comparison with their previous behaviour.”
Still, the study is far from spelling a bright future for corals, says Dr John Burt, an associate professor at New York University Abu Dhabi. He says that Dr Ben Romdhane’s findings are in agreement with a paper published last year by scientists at the University of Southampton, which used remote sensing to examine bleaching patterns in Abu Dhabi in 2012.
“The Masdar results reflect what we had observed, in that there was lower bleaching around Dalma Island than what we had anticipated,” says Dr Burt, the head of the university’s marine biology laboratory.
“This likely has to do with the higher abundance of stress-tolerant Porites corals at Dalma, as well as possible buffering effects from the deeper surrounding water.”
Dr Burt said a more detailed look, covering even larger areas of reef over longer times, was necessary before conclusions could be made about the future of Gulf reefs.
Their increased resilience as shown by the recent studies could do with earlier deaths of more sensitive coral species. “These shifts in community composition have already been well documented in Abu Dhabi, and there are open questions as to whether the remaining relatively stress tolerant species can continue to cope with increasing temperatures,” says Dr Burt.
“Data from our lab suggests that even these hardy species are living close to their thermal limits, which does not bode well for the future of these reefs under climate change.” Dr Ben Romdhane’s work is laying the foundation for further large-scale monitoring of the UAE’s reefs and for assessing their possible reactions to future challenging conditions.
Another key contribution of the study is the discovery of a reef off Dalma Island, which was not known to scientists or environmental authorities. The reef spreads to a territory of 1 square kilometre and features large, healthy corals.
Stuart Phinn, professor at the School of Earth and Environmental Sciences at the University of Queensland, says he is familiar with Dr Ben Romdhane’s work after having met her and other UAE researchers at a scientific conference last year. Her paper is one of more to come, he says, as researchers all over the world have started using advances in remote sens- ing technologies in the past five years.
“Coral reef mapping and health condition monitoring is really 10 to 15 years behind what has happened with our terrestrial forests and vegetation,” says Prof Phinn, director of the university’s remote sensing research centre.
“We have operational mapping of species, structure and height, biomass and condition of vegetation on the ground but doing it under the water has been a lot more challenging and taken a lot more time.”
Prof Phinn says that while the technique does not eliminate the need for field work, it can provide valuable insights.
“With any sort of environmental monitoring and management – it does not matter if it is a local government doing it, a country or a community group that is responsible for an environment – the way that you make sure that you can keep using that environment and looking after it is by knowing what is there and how it is changing over time.”
‘ Coral reef mapping and health condition monitoring is really 10 to 15 years behind what has happened with our terrestrial forests and vegetation Prof Stuart Phinn University of Queensland