Going Beyond 'The Beach': Thailand Reef Biotope

The Thai island of Koh Phi Phi Leh had been high on my list of places to visit ever since watching Danny Boyle’s screen adaptation of Alex Garland’s novel ‘The Beach’ in the mid-2000s. Propelling the real-life cove of Maya Bay into the mainstream, the film's portrayal of golden sands, turquoise water and towering limestone cliffs fringed by tropical jungle created an image of paradise unlike anything I'd seen before. All I could do was imagine the seascape awaiting beneath the waves. 

Any doubts that the marine life here wouldn’t live up to expectations were immediately quashed on the ferry over from Phuket. Huge shoals of flying fish (family Exocoetidae) took flight across the bow, while a pod of spinner dolphins (Stenella longirostris) temporarily acted as cetacean chaperones, directing us on our way. With our accommodation situated a stone's throw from the Tonsai pier docking point, we were eager to get in. We booked a couple of dives for the following day at a local dive centre before heading across to Loh Dalum to see what the shallows had to offer.

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For more Marine Biotope inspiration read: 

Red Sea Biotope Aquarium: A Guide to Reef Zones, Fish & Setup

Salt and Spice: Caribbean Reef Biotope

Life in the Shallows of Thailand's Seas

With just algal-covered, rocky outcrops punctuating the sandy substrate, our first impression was just how muted this initial underwater landscape was. The blue skies, golden beaches and rich green foliage had given way to a sandy brown beneath the surface.

Photo by Chris Sergeant

But despite appearing barren, this habitat was anything but – you just needed to look a little closer. Various crabs negotiated the crevices created among the rocks, while a pair of well-camouflaged messmate pipefish (Corythoichthys haematopterus) snaked their way through the algal turf, unperturbed by our presence. 

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Tiny subterranean burrows pockmarked the sediment, and our attention was drawn to one particular dwelling where clouds of sand emanated from the entrance. Here, a colourful pinkspot goby (Cryptocentrus leptocephalus) dashed about, picking off microinvertebrates, while behind it, a pistol shrimp (Alpheus sp.) was busy engaging in a spot of home improvements.

Kicking out away from shore, as the depth increased, so did the fish numbers. Indian redfin butterflyfish (Chaetodon trifasciatus) and juvenile bridled monocle bream (Scolopsis bilineata) buzzed around, pecking at the algae carpet, while a striking floral Maori wrasse (Cheilinus chlorourus) scoured the base of the rockwork for crustacean prey.

Shoals of whitetail damselfish (Pomacentrus chrysurus) would angrily remonstrate with us, while their bolder and braver Pomacentridae cousins, the Indo-Pacific sergeant majors (Abudefduf vaigiensis), would barrel over, semi-expectant of being fed. Amongst all this damselfish fury sat a snowflake moray (Echidna nebulosa), partially hidden under a ledge. 

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As well as the silt-enrobed algae, Padina started to appear along with the occasional Porites colony, almost always a grey-brown, sticking with the sandflats' primary aesthetic. A well-disguised carpet anemone (Stichodactyla sp.) lay half-buried beneath the sediment, whether through wave action or by deliberate design.

With the sun starting to set, we finned back to shore, stumbling across a magnificent anemone (Radianthus magnifica) on the way. Ducking down for a closer look, we were greeted by a pair of feisty ocellaris clownfish (Amphiprion ocellaris), who would dash from their tentacled safe-haven to deploy a few tactical nips to our mask straps. 

Photo by Chris Sergeant

Related article: Are Damselfish Suitable for a Community Reef Tank?

Recreating this Habitat

Encounters like these demonstrate that even seemingly barren sand flats can support an extraordinary diversity of life. Better still, it's a habitat that's surprisingly achievable in the home aquarium.

A deep coral sand bed, scattered live rock, a few clumps of macroalgae, and plenty of open space will capture the natural feel of these shallow coastal flats. Leaving large areas of open substrate is just as important as the rockwork itself. It allows gobies, shrimps and other sand-associated species to display the natural behaviours that define this habitat.

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For a simple display, a pistol shrimp paired with a pinkspot goby (or two if you can find a pair) would make a fascinating centrepiece. They are a perfect example of mutualism, with the goby standing guard while its crustacean partner tirelessly excavates and maintains their shared burrow. A pair of messmate pipefish would add gentle movement throughout the aquarium, reinforcing the tranquil nature of this shallow-water habitat.

More experienced reefkeepers could instead centre the aquarium around a magnificent anemone and its resident ocellaris clownfish. Allowing the host anemone to become the focal point, surrounded by open sand and minimal rockwork, creates a display that closely mirrors the natural habitat seen around Koh Phi Phi.

Whitetail damselfish are another species worth considering. Although less commonly encountered than many other damselfish, they occasionally appear in the trade and add constant movement to the upper levels of the aquarium. As with most damselfish, territorial disputes become more pronounced with age, so they're best maintained either singly or in large groups within spacious aquariums, where dominant individuals are less able to focus their attention on a single tankmate.

Biotope Tip: Resist the temptation to overcrowd this aquarium with corals. The beauty of Thailand's shallow coastal habitats lies in the contrast between open sand, isolated rocky outcrops and the fascinating behaviours of the animals that inhabit them.

Shark Point: The Transition to the Reef

The primary goal of visiting Shark Point was to encounter the resident blacktip reef sharks (Carcharhinus melanopterus) rather than to gain inspiration for biotope aquariums back home. However, there was still plenty of inspiration to be found here. 

As at Loh Dalum, we were swarmed by a welcoming party of Indo-Pacific sergeant majors, darting around just beneath the surface. Navigating our way through the black and blue stripes, the rocky substrate opened up in front of us. Here, coralline algae smothered parts of the rocky reef, while colonies of brown Montipora formed bommies in between the broken rubble.

Photo by Chris Sergeant

A closer inspection of the rockwork revealed a host of invertebrates taking up lodgings. Various crabs patrolled the crevices, while a striking varicose wart slug (Phyllidia pirobra) crawled over an aggregation of Christmas tree worms (Spirobranchus sp.), its vivid, aposematic blue and orange markings completely at odds with its otherwise silty and brown backdrop.

A splash of colour was also provided by a few of the new fishy faces. Red-tailed butterflyfish (Chaetodon collare) were pecking at the coral, while small shoals of freckled goatfish (Upeneus tragula) rooted about in the sand.

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Numerous wrasses dashed about the reef, with these piscine balls of endless energy only identifiable as checkerboard wrasse (Halichoeres hortulanus) and moon wrasse (Thalassoma lunare) during their brief pauses to peck at something attached to the boulders strewn across the seabed. If we ever needed proof of why even modest-sized wrasses require larger expanses of aquascaped rockwork over which to patrol, this was certainly it.

Another highlight here was chancing across a pair of copperband butterflyfish (Chelmon rostratus) out for a breakfast date, utilising their elongated rostrums to scour the rocks for their micro-crustacean prey. 

Photo by Chris Sergeant

The stars of the show, however, were undoubtedly the sharks. Prowling over the seabed, gliding just above the rubble, they would come to just a matter of metres away, before rising up and turning sideways to check us out. Should we stray too close, then they would slip back into the blue with an effortless flick of the tail, only to be replaced by another, equally curious carcharhinid.

Instead, replicating this habitat in a large, spacious aquarium means shifting focus to the butterflyfishes and wrasses set against a Montipora-dominated seascape.

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Biotope Tip: Many butterflyfish (including the red-tailed) will readily eat live stony corals. To safely replicate this seascape, consider a Fish-Only With Live Rock(FOWLR) system using skeletal rock work, or focus instead on the copperband, which is less likely to harm SPS corals like Montipora. 

Corals of Fingers Reef

Dropping down onto Fingers Reef, it was difficult to know where to look first, as the dive immediately felt like swimming through an immersive dive guidebook, with familiar faces at every turn. Any concerns we had about reef aesthetics not living up to expectations were instantly washed away by the healthy coatings of low-growing corals carpeting the rockwork.

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Branching colonies of yellow and blue Acropora poked over the top of the more encrusting-type Porites. Intricately decorated lesser star corals (Goniastrea pectinata) attached themselves to any unoccupied gaps on the rocks, along with small, fragmented Favia and Platygyra colonies, while flatter finger leathers (Sclerophytum sp.) grew into colonies far larger than I’ve seen previously.

Photo by Chris Sergeant

Lower down, the reefscape was equally busy. A few flowerpot corals (Goniopora sp.) sat nestled on the sand, while numerous disc corals (Ctenactis sp.), along with the more circular Lithophyllon and Fungia, lay stretched out wherever they felt like. For any reefkeeper inspired to design a biotope based on this part of the world, the coral combinations and opportunities here felt endless.

Related Article: Back to saltwater: starting simple with beginner corals.

Lyre gorgonians (Ctenocella pectinata) and orange sea fans (Subergorgia suberosa) stood tall as we finned past, providing three-dimensional structure, while armfuls of eclectic, bushy feather stars (family Comatulidae) littered the base of each. Many played host to a mix of micro-crustaceans and nano gobies—all too small to identify—buzzing about the vertical forms.

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It was always worth checking to see who was residing among them, a point affirmed later by the discovery of a pair of ornate ghost pipefish (Solenostomus paradoxus) oriented head-down, hiding among the fronds of one particular Menella sea fan. These fish may feel like the ultimate reef showpiece, but before prospective aquarists get too many ideas, their reduced digestive system means an insatiable need for a constant supply of Mysis, making transporting these delicate fish fraught with difficulty. Coupled with a general lack of knowledge regarding captive care, this genus is best left in the wild.

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There were countless invertebrate representatives on display here too. Numerous large, blue linckia starfish (Linckia laevigata) and a few common comet stars (Linckia guildingi) roamed over the rockwork – a mobile banquet in the eyes of the elusive harlequin shrimp (Hymenocera picta) that supposedly roam these parts.

Fishes of Fingers Reef

Flitting above the reef itself were scores of golden damselfish (Amblyglyphidodon aureus), yellowbelly damselfish (A. leucogaster), lemon damselfish (Pomacentrus moluccensis), and various wrasses. In the distance, great herds of convict surgeonfish (Acanthurus triostegus) poured over the rocks, interspersed with different parrotfish and orangestripe triggerfish (Balistapus undulatus).

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A closer look among the corals also revealed a few other aquarium regulars. White-eyed morays (Gymnothorax thyrsoideus) snaked their way across the rocks, roaming between crevices, while zebra lionfish (Dendrochirus zebra) and spotfin lionfish (Pterois antennatus) made their home under larger coral colonies, resting head-down in the shadows.

Our guide then beckoned us over to an Acropora outcrop, pointing excitedly into the middle of the branching structure. Noting that I couldn't spot anything, he put his fist to his head, leaving just one finger sticking out—like a lure. Ahh, the universal dive sign for a frogfish! Gauging that I had finally twigged, he pointed again, this time just an inch or so from the coral tips. Tucked deep inside the branches was a giant frogfish (Antennarius commerson), exceptionally camouflaged within its coral home.

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On the substrate, bluespotted maskrays (Neotrygon kuhlii) busied themselves foraging for buried treasure, while an enormous giant moray (Gymnothorax javanicus) stretched out from its lair. In addition, almost every overhang we passed played home to a few common lionfish (Pterois volitans), and the deeper we went, the larger the individuals seemed to be.

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The other larger species dominating the seascape here were bigeye snappers (Lutjanus lutjanus). With a maximum length of 35cm (14”), they aren’t huge fish individually, but when they mass together in one giant shoal, it’s an impressive spectacle. Pausing for a couple of minutes to watch them stream past, the clouds of yellow blurred out the rest of the reef. When we talk about shoaling species from an aquarium perspective, we often refer to numbers like 6 or 12, but the reality is, if we wanted to match those that occur in nature, we are missing a few zeros!

Building the Biotope

A Fingers Reef biotope allows for a much stronger focus on corals and sessile invertebrates. To recreate this vibrant seascape:

• Rockwork Structure: Cover your live rock base with encrusting and branching stony corals like Acropora, Porites, Goniastrea, Favia, and Platygyra, alongside leathers such as Sclerophytum.

• Sandbed & Base: Place free-living or substrate-associated corals around the rock base, including Goniopora, Ctenactis, Lithophyllon, and Fungia.

• Vertical Accent: Supplement with yellow sponges or gorgonians (Ctenocella, Subergorgia, or Menella) to add height and complete the Fingers Reef profile.

Biotope Tip: Select fish species based strictly on your aquarium volume rather than choosing larger species that you like the look of and planning to upgrade the tank as they grow.

Carpets of Anemones at Koh Bida Nai

Our final dive stop was the sister island of Koh Bida Nai. Descending to the seabed, carpets of magnificent anemones were laid out before us. It was hard to determine where one finished and the neighbouring anemone started. Each was heaving with a mix of skunk clownfish (Amphiprion akallopisos) and larger Clark’s clownfish (Amphiprion clarkii), while domino damselfish (Dascyllus trimaculatus) danced about above the tentacles.

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A pair of bluestreak cleaner wrasses (Labroides dimidiatus) optimistically rose up from their cleaning station below, offering their services, while ornate wrasses (Halichoeres ornatissimus) and half-and-half wrasses (Hemigymnus melapterus) cruised about, injecting a colourful but chaotic element into the mix.

Photo by Chris Sergeant

Drifting slowly around the site, we counted Java rabbitfish (Siganus javus), longfin rockcod (Epinephelus quoyanus), and the occasional spotted coral grouper (Plectropomus maculatus) as we went. Glancing up towards the surface, a large shoal of barracuda had started circling directly overhead. Given the proximity of the two islands, the coral composition was closely aligned with that at Koh Bida Nok, although we did notice a few small Coelastrea and Dipsastraea colonies dotted about as well.

A stream of Moorish idols (Zanclus cornutus) shot past in formation, disturbing a perfectly camouflaged scorpionfish (Scorpaenopsis diabolus) hidden on the nearby rockwork. A quick flare of its pectoral fins was a clear warning to the Moorish idols – and us – that we had strayed too close. Given its venomous capabilities, we respectfully retreated.

Photo by Chris Sergeant

Nearby, a collection of rubble lined the entrance to a subterranean dwelling, and with a little patience, we were rewarded with a visit from the homeowner: a sizeable peacock mantis shrimp (Odontodactylus scyllarus). After a brief spot of burrow renovation, the stomatopod scuttled off in the direction of the nearby reef without as much as a sideways glance.

Even during our ascent, we were treated to one final sight: high in the water column, well above the reef, was a group of monos (Monodactylus argenteus). Typically offered in the trade as brackish dwellers, this group was miles from the nearest freshwater outlet – a timely reminder that adults such as these ultimately require a fully marine setup.

Bringing Koh Bida Nai Home

There are several exciting approaches to recreating a Koh Bida Nai biotope in the aquarium:

• Marvellous Mantis Shrimp: Dedicate a species-only aquarium to housing a peacock mantis shrimp. Offering fascinating intelligence, interactive behaviours, and a vivid rainbow of colours, this setup simply requires a deep substrate and plenty of rocky caves to create a standout display.

• Perfect Pomacentridae: Recreate the anemone meadow using a large display centred around a group of clownfish. Domino damselfish alongside the robust Clark's clownfish could work nicely, though keep in mind that dominoes lose their stark white spots as they mature and that anemones can capture unsuspecting fish. 

• Monos and Corals: Much like the Fingers Reef concept, you can build a coral-dominated reef paired with a fast-moving shoal of adult monos occupying the upper water column and colourful wrasses patrolling the rocks below. Remember, though, monos grow large and will need a huge reef to thrive. In hobbyist systems, the ghost cardinal (Zoramia leptacantha) would give a similar silver shoal in a much smaller package. 

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Biotope Tip: If attempting the "Anemone Meadow" biotope, ensure you cover your wavemakers with guards. Anemones like to move around, and can get sucked into pump intakes. 

An Important Reminder

As the dive boat navigated its way back to shore, we peeled off on a quick diversion into Maya Bay itself – clearly a well-trodden path for dive operators here. Terrestrially-speaking, the view was breath-taking, but below the surface was a different story.

As we entered the bay itself, one of the divemasters mentioned that ‘sometimes we have boats queuing up outside the entrance to take their turn dropping people off’, and the impact of this unchecked tourist influx, that we were unwittingly now a part of, was clear. Broken, anchor-damaged rubble dominated the reefscape, and while we found a few Ctenactis, the majority of corals in that patch of the bay were damaged fragments. If that wasn’t bad enough, spread out amongst them sat a number of extremely large crown-of-thorns (Acanthaster planci) – talk about taking a kicking when you're down.

Thankfully, the Thai authorities closed the bay shortly after our trip, citing environmental damage caused by the excessive tourist numbers and it remained shut for a few years before re-opening more recently with much tighter restrictions.

The benefits to the marine life are clear. As in the film, sharks now utilise these enclosed waters once more, while visible coral regrowth is working to bring back many of the reef-builders, and dwellers, that had deserted the area not so long ago. "These things show that nature will heal if we give it time” as the Thai Tourism Authority once said. 

This article was first publish in the June 2026 issue of Practical Fishkeeping, subscribe today to never miss an issue.