Turbulent times for turbid reefs: riveting research in the Gulf of Thailand
Sophie Coxon uncovers the wonders of Thailand’s turbid reefs - a largely unstudied ecosystem which could hold the key to climate-resilient corals.
Article by: Sophie Coxon
Artwork by: Amber Rodemeyer
A flat turquoise ocean, studded with lush green islands, gleams in the midday heat as the towering form of storm clouds roll across the horizon. Soon, the peace will be broken and an indigo blur of monsoon rain will blend sky and sea. Bleached and broken fragments of coral skeletons litter the beach, a sharp reminder of the struggle being fought below the surface. But this battle is a silent one, an invisible one, to us up here on land. Its impacts are buffered and cushioned by nature’s many facets, and the true depth of its effects will not be felt until it is too late. The paradise that is the Gulf of Thailand hosts some of the most resilient, tough and hardy reef species around, but signs of distress are becoming more apparent. Turbid reef ecosystems may be naturally sculpted to endure hardship, but there is a limit to how much they can take - and we may have crossed the line.
Turbid reefs are little-known, understudied, largely ignored ecosystems found across global coastlines, characterised by unusually high levels of sedimentation and algal growth. The abundance of silt, sand and organic particulate matter floating in the water column causes water clarity, and hence visibility for divers and snorkelers, to be much lower than the classic coral reef image most people imagine. In turbid reefs, there are no crystal-clear views of sparkling rainbow coloured corals or picturesque scenes of fish shimmering in the distance. These reefs are rich in other ways, appeasing to functionality rather than aesthetic appeal, and are particularly resilient to external stresses, such as nutrient loading, salinity changes and temperature increases - all of which are intensifying with climate change.
The less photogenic nature of these reefs repels tourism, diminishes public interest, and consequently, shrinks scientific investment. This is possibly felt most strongly in the Gulf of Thailand, where the disparity between reef type, diving popularity, and research attention, is glaring.
The Gulf itself boasts unusual ecological conditions. Naturally high water temperatures occur due to its shallow seabed and enclosed geology, and the abundance of large river estuaries along the southern, western and northern coastlines contribute huge inputs of freshwater, laced with pollution. This facilitates the growth of phytoplankton, which adds to the jade-green tint of the water and reduces water clarity.
Nestled in the southern end of the Gulf, between Koh Samui and Koh Tao, lies the island of Koh Phangan. This island is a jungle-covered expanse of mountain, swooping downwards to blonde sand beaches and shimmering bays. Turbid reefs fringe the coastline, softening the impact of waves and bearing the brunt of storms which commonly blow across the island. Based on the north coast is a research station, where I worked in a team of scientific divers, collecting data on the current state of the reefs. We lived and worked in the bays, laying transect lines, recording coral cover, monitoring fish species, and photographing bleaching over time.
The reef is very much alive, despite it seeming less ‘biodiverse’ or ‘ecologically vibrant’ upon first impressions. It can be disconcerting to plunge into the water, and only be able to gauge what's around you for a few metres. But this is no reason to turn our noses up and seek wonder elsewhere; these reefs have quirks and magic all of their own, and it just takes a little more effort to see it.
Hundreds of species of fish, many of which drive the fish markets in local villages, thrive within these reefs, feeding on the abundance of coral, algae, and other organisms. Canyons of ancient corals, some hundreds of years old, form an underwater kingdom of orange and brown, glittering with oysters and barnacles. The seafloor is embellished with giant clams, which filter nutrients from the water, purifying it like trees on land. Schools of parrotfish shine like iridescent crescents of rainbow, swooping across the reef as they scrape bites of algae and leave a trail of white dust behind. Dainty pairs of butterflyfish dance in and out of coral branches, golden stripes shimmering as they pluck fervently at polyps.
As scientific divers, we were blessed with the time and the need to spend long periods on these reefs, watching them, analysing them, loving them. And it didn’t take long - the very fact that few other people had ever made the effort to get to know these reefs is reason enough to feel connected to them. From the fronds of brown algae, swaying in the current, to the honeycomb groupers perched on their sponge cushions, every feature and facet of the ecosystem revealed its magic and charm in unexpected ways.
The sediment which veils these reefs, from both sunlight and recreational divers, is naturally deposited into the shallows from the islands, particularly throughout the monsoon season. Whilst on most reefs, sedimentation is a largely damaging input, here it may act as a protective layer, reducing the effect of UV rays and decreasing the chance of coral bleaching. The native corals, such as bouldering species of porites and branching acropora, are acclimated to the turbid conditions and can cope with excessive sedimentation by producing a mucous layer which sloughs off any debris. Fish and other fauna have heightened eyesight, olfactory detection and specialised camouflaging, burying themselves in the sediment to hide from predators or ambush prey.
During the research period, a heatwave hit the gulf, scorching the beaches and provoking furious, grumbling storms. One searing day in June, the water reached 34 degrees Celsius, a heat so intense even the monsoon rains couldn’t cool it down. The sea simmered, and the plankton bloomed. Rapidly. A great green cloud, blossoming from the south and spreading across the gulf, swept into the bays and over the reefs. Visibility dropped to below a metre and everything was cloaked in a thick, greenish tinge.
The corals, which had been teetering on the edge of stressed, were suddenly tipped over the edge and could no longer hold out. With every dive, more and more patches of glowing white could be seen across the reefs as they succumbed to the disaster that is bleaching. It was distressing to watch, as a powerless scuba diver, our work and passion - the entire reef - begin to shrink and degrade.
On top of existing pressures - the swathes of chemical and sewage pollution pouring in from the rivers, the loss of mangroves and seagrass to make way for luxury resorts, and the intense overfishing of the entire gulf - the added stress of extreme heat and plankton overgrowth is too much. The most resilient reefs around are faltering and bleaching, and though they may recover, the damage will cause huge loss to biodiversity and humans alike.
One of the largest problems we face as researchers working on Koh Phangan’s reefs is the absence of existing, long-term data for us to compare our results to. There is a gaping hole in the literature, with almost no previous research conducted on turbid reefs in Thailand or other southeast asian countries, presenting an obnoxious challenge in navigating conservation and protection of these ecosystems.
Understanding these reefs is essential for providing us the tools we need to protect marine ecosystems from extreme degradation and total loss, which is a very possible outcome. These resilient corals could hold the key to protecting other reefs from climate change. Sometimes the beauty and importance of something is not always obvious until it's too late. We may not feel its presence, but we will feel its loss.
The message is loud and clear - global warming is going too far too fast. The mechanisms behind the elevated resilience exhibited by corals native to turbid reefs need to be uncovered, so that new methods of reef preservation and recovery can be developed before total collapse occurs. And, in the meantime, the core issues of climate change need to be addressed. It is time to stop fussing with the leaves and deal with the root.