By Sophie Coxon
The island is washed into the water, clouding the blue sea green, shielding the reefs from the searing sunlight and settling in a blanket of soft murk over the undulating coral landscape.
A tidal wave of coral research and restoration has swept the global oceans and lapped at shallow coastlines over the past few decades, spurred by the increased appreciation for coral reef ecosystems and the value these habitats contribute to planet Earth. The kaleidoscopic kingdoms of sunlit reefs, sparkling in crystal clear waters and pulsing with shoals of fish, turtles and the shadows of sharks, attract a huge influx of attention due to their aesthetic appeal and hence receive the majority of research funding. But other kinds of reef exist, and may hold invaluable resilience to pressures and stresses which could unlock new hope for the future of conserving the planet’s struggling coral reefs. If we can look deeper than surface-level appearance and place value in grittier realms, the tools required to combat coral reef decline may be within reach.
The island of Koh Phangan is well stamped on the maps of young backpackers and travellers, known for its infamous full moon parties and zen yoga community. The island acts as a stepping stone for divers on their way to the marine paradise of Koh Tao, one of the world’s most heavily dived regions, famed for its vast coral reefs, anemone beds and vortexing tornadoes of trevally and barracuda. However, the reefs of Koh Phangan, only a few kilometres south, lie relatively unscathed by the bubbling swarms of divers. This is no doubt due to the fact that these reefs are turbid, exhibiting vastly different ecological conditions to the crystalline water column and flamboyantly technicolour reefs of Koh Tao. In the summer of 2024 I spent three magical months on this island, and my understanding and appreciation of these cloudy, silted, plankton-infused reefs took spark.
Turbid reef systems are significantly understudied in comparison to their oligotrophic counterparts, though are beginning to gain interest as the struggle to develop long-term coral restoration techniques intensifies. Characterised by high levels of suspended sediment, increased algal cover and low coral diversity, turbid reefs inhabit vast areas of shallow tropical and temperate coastlines, including 30% of the Coral Triangle, the most biodiverse reef region on the planet. High sedimentation levels are often classified as a stress to coral reefs, however naturally turbid systems are well adapted to these murky conditions, and may even benefit from the abundance of silt, plankton and organic matter that enshrouds them.
Whilst corals growing within turbid ecosystems exhibit slower growth, they also show improved stress tolerance, reduced bleaching and lower mortality rates than those in non-turbid systems, and are robust against the plethora of pressures burdening shallow ecosystems provoked by climate change and growing anthropogenic exploitation. Recent research has suggested that the suspended particles reflect a large percentage of UV radiation which exacerbates bleaching, and the inhabitant coral colonies are accustomed to being smothered by sediment, constantly producing mucus which sloughs off any surface debris. Plainly put, turbid reef systems are not the picturesque kingdoms of tropical colour and aquatic enchantment that springs to mind with the words ‘coral reef’, however the biodiversity they harbour and ecological services they supply are no less important.
I was integrated into a team of researchers at the COREsea station on the north shore of the island, spending long days diving in the various bays collecting data for long-term monitoring projects, as well as conducting my own research study on fish assemblages across reef zones. We assessed reef substrate composition, bleaching cover, coral predators, fish communities and giant clam abundance across the survey sites, compiling everything in a decade-long data archive – a live picture of the trends, dynamics and fluctuations occurring on Koh Phangan’s murky reefs. No other similar research has been published on this specific region, leaving a gaping hole in the scientific literature and our understanding of Thailand’s tropical turbid reef systems.
Though naturally turbid and rich in organic matter, with the onslaught of development and increasing tourism, Koh Phangan’s reefs are becoming inundated with threats. Construction and forest clearing on the island’s junglish slopes loosens sediments, which are rapidly washed into the surrounding coastal waters with every monsoon downpour. The footprint of the tourist industry is also leaving its mark, with pollution and disturbance accelerating every year, combining with the effects of climate change to push the already overfished and exploited reefs to the edge.
Researching these ecosystems is crucial to protecting and preserving them; without establishing biodiversity baselines and monitoring the temporal changes occurring, it is impossible to predict future outcomes and support new protection measures that may be fundamental to preventing degradation.
Throughout my time working on these reefs, I became closely familiar with the patterns and quirks that instilled a certain charm to the ecosystem. There was as much beauty here as any other reef I had dived, it just took a more willing eye to see it. After only a few days, I felt at home in the greenish murk, the glowing white streak of the transect line the only sense of direction in the vast expanse of coral canyons, pillars and plateaus that stretched out around me. Nudibranchs could be found speckled across the boulder corals, where pairs of butterflyfish sucked corallites through puckered lips and cushion stars lay, plump and velvety, like pincushions placed on coral plates. The jade-tinged haze of the water cloaked everything in mystery, blurring the silhouettes of fish into translucent shadows and suggestions, obscuring the treasures of the reef from all but the most vigilant observers. However, the blinding white scars of bleached coral gradually became more and more abundant across the reefs, like warning beacons signifying the beginnings of a disaster.
Not long into my stay, an ocean heatwave singed the globe, and the Gulf of Thailand simmered. As sea temperatures soared into the mid 30s (Celcius), a plankton bloom engulfed the bays and the visibility dropped to between 1 and 2 metres. The water column was thick and green, and the monsoon rains sent rivers of sediment pouring onto the reefs every afternoon. The dives went on, and we continued monitoring the reefs, watching them turn a ghostly white before us. By the end of my three month research period, huge areas of the reefs were completely bleached, and finding a coral that was unscathed by bleaching was near impossible.
Whilst bleaching is not immediately fatal, if conditions remain inhospitable for a lengthened period, many coral colonies, some close to a century old, may succumb to this slow and pallid death, leaving nothing but empty skeletons to dissolve in the acidic seawater that once gave them life.
The snapshot of coral bleaching I was exposed to throughout my research period was both eye-opening and eye-watering. The severity of the issue was branded into my mind with every subsequent dive, the tally marks in the ‘fully bleached’ column multiplying each time, filling the clipboard with grim black smudges. The toughest, most resilient reefs we know of are now failing under the crushing weight of climate change and human interference. But the future of these reefs can still be steered towards vibrancy – to lose them would mean a loss of food and livelihood for the hundreds of local communities who call the Gulf of Thailand home, and would have deep-rooted impacts across marine food webs, affecting biodiversity throughout a vast region of ocean. The cushioning effect provided by the toughened forms of ancient bouldering corals would leave coastlines open to the elements, and the fronds of life on the reef, woven tightly into the tapestry of the local cultures and traditions, would be lost.
There is more to turbid reefs that initially meets the eye, and we must enrich our understanding, connection and appreciation of these systems to grant them a place in our restoration frameworks. With more research, like the work carried out by the dedicated team at COREsea, the mysteries of these reefs and the limits of their resilience can be uncovered and shared across global reef conservation.
This piece was prepared online by Panuruji Kenta, Publisher, SEVENSEAS Media