NAD Lembeh

If there is one feature on a nudibranch that immediately draws your attention, it is the pair of horn-like structures perched on their heads. Known as rhinophores, these delicate organs are essentially the sea slug’s primary sensory antenna, serving as their nose and taste buds all in one. Because nudibranchs have very rudimentary eyes that can only detect light and dark, they rely almost entirely on their rhinophores to navigate the reef, locate prey, and track down potential mates.

The sheer variety in rhinophore design across different species is incredible. To maximise their surface area for detecting faint chemical scent trails carried in the current, these organs are often heavily textured. Some species possess rhinophores that look like folded feathers or tiny pine cones, while others feature intricate rings, clubbed tips, or smooth, whip-like points.

Because rhinophores are so critical to their survival, they are also a prime target for hungry fish. To protect them, many nudibranchs have evolved specialised pockets or sheaths where they can instantly retract their rhinophores when they feel a shadow pass overhead or detect sudden turbulence. Capturing these fine, complex structures in crisp focus is often the key to a great macro shot, highlighting the remarkable engineering built into these small marine molluscs.

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During blackwater dives, encountering juvenile fish out in the open water column offers a clear view of just how drastic marine transformations can be. Many species look and act completely different in their larval and pelagic stages compared to when they eventually settle onto the reef, using temporary adaptations to survive their early life in the blue.

A classic example of this shift is the juvenile Barred Soapfish. At this stage, it sports a bright yellow body and dramatically elongated dorsal fin filaments. These long, trailing streamers are thought to mimic the stinging te****les of siphonophores or jellyfish, serving as an effective visual deterrent against open-water predators.

As they mature and transition to a benthic lifestyle, these temporary features disappear. The long dorsal filaments recede, the vivid yellow tone becomes much more subdued, and the fish develops the dark, vertical grey bars that give the adult its name. Photographing these pelagic juveniles in midwater captures a brief, highly specialised phase in their lifecycle before they make their permanent home on the seafloor.

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Finally have the books onsite. Pick up a copy when staying with us!

Finally have the books onsite. Pick yours up when staying with us!

While the males draw immediate eyes with their fiery, high-contrast red heads, the female Lyretail/Steene's Dottyback has a completely different, understated charm. Wearing a deep slate-to-bluish-grey tone across her entire body, her uniform colouration allows her to melt into the dark crevices and shadows of the rubble slope.

What makes their biology even more intriguing is that these fish are protogynous hermaphrodites. Every Lyretail Dottyback starts its mature life as a female. If the dominant local male disappears, the largest female in the area will actually undergo a complete s*x change, transforming her grey-blue body and adopting the bright, fiery orange head of a male to take over the territory.

Photographing a female is a true test of patience, as these fish spend their days darting relentlessly between small holes and rock overhangs. If you look closely at her profile, you can catch the sharp, visible teeth and aggressive jawline that define these small reef predators. While less flashy than the males, her subtle blue tones and delicate fin structure make for a fantastic portrait, capturing a fleeting phase in a remarkably adaptable lifecycle.

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The Coconut Octopus stands apart on the muck slopes due to its remarkable problem-solving ability. On open, featureless sand flats where natural cover is practically non-existent, this species relies heavily on tool use to stay safe from predators. Once it finds a suitable pair of large clam shells, it will haul them vast distances across the silt until it finds the right spot to settle.

Watching how they manipulate their mobile shelter is fascinating. The octopus digs a shallow depression in the sand, fits its body snugly into one shell, and then pulls the second half over, sealing every te****le inside. It turns two separate bivalve shells into an impenetrable fortress, holding them tightly shut using the suction of its te****les.

When they are enclosed like this, patience is everything. If you rest quietly nearby without disturbing the sand, the octopus will slowly push the shell open just enough to survey its surroundings. Capturing that moment—with those large, intelligent eyes peering out from between the gap of the two shells—highlights both the detailed texture of their suckers and the incredible adaptability of these reef intelligent invertebrates.

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The Janolus family of nudibranchs stands out as some of the most striking sea slugs found on the reef. Easily recognised by the dense forest of soft, translucent spikes covering their backs known as cerata.

Unlike many other nudibranch species that carry their gills in a single tuft near the rear, Janolus species feature digestive and respiratory branches that extend directly into these cerata, which also store defensive toxins derived from their food.

One of the defining identification features of this group is the strange, wrinkled crest positioned directly between their two main head te****les (rhinophores). Known as a caruncle, this sensory organ helps the nudibranch detect chemical signals and currents in the water column, immediately distinguishing a Janolus from similar-looking aeolid nudibranchs. The tips of their cerata often feature bright, high-contrast colours ranging from deep blues to vivid golds, serving as a clear warning to potential predators that they taste foul.

These nudibranchs are highly specialised feeders, residing on colonies of bryozoans, or moss animals. Finding them usually involves scanning bryozoan patches along reef walls, rock overhangs, or rubble slopes. Because they are delicate and can drop their cerata as a distraction when threatened, watching them move undisturbed offers a clear view of their unique anatomy.

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An adult Tiger Mantis Shrimp completely out of its burrow is a rare sight, but finding one swimming in midwater near the surface during a bonfire dive is almost unheard of. These large spearers are built for a life anchored inside deep sand tunnels, leaving only their eyes exposed. Seeing a fully grown adult abandon its burrow to travel up the water column towards the dive lights is a major departure from their usual habits.

Out in the open water, the true scale and structure of the crustacean become fully visible. Without the sand concealing it, you can see the entire length of its heavily armored, zebra-striped body and its large spearing appendages. It is a completely different perspective on an animal that is typically viewed as a stationary ambush predator on the seafloor.

Photographing this individual right at the surface film allows the calm water to create a clear reflection. Capturing the symmetry of its distinct bands and stalked eyes mirrored against the dark surface provides a unique macro frame. It serves as a reminder that even the most dedicated bottom-dwelling species in the Strait can occasionally surprise you by venturing into the open water column at night.

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Ever tried looking for a fish that is actively pretending to be a leaf? The Halimeda Ghostpipefish has mastered the art of hiding in plain sight, living almost exclusively among patches of Halimeda algae. This green, segmented seaw**d grows in distinctive, coin-shaped discs, and the ghostpipefish has evolved an anatomy that mimics these flat segments down to the very last millimetre.

Every single feature of this species is designed to maintain the illusion of drifting vegetation. Their bodies are remarkably compressed, matching the bright green tone and rounded shapes of the algae plates. Unlike other ghostpipefish that might sport long filaments or transparent patches, the Halimeda variety stays compact and smooth, often drifting head-down in the slight current right next to a real leaf. They even mimic the tiny white calcified edges of dead algae segments to throw off predators.

Finding one requires slowing right down and watching the base of the algae clumps for any movement that doesn't align with the surge. Because they are often found in pairs, spotting one could mean a second is hovering close by. Observing this level of extreme evolutionary specialisation is a perfect example of how complex life on the muck slopes can get, turning a basic w**d patch into a spectacular find.

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