Nudibranchs and the Spanish dancer

Nudibranchs belong to a group of marine molluscs called opisthobranchs. They shed their shells after the larval stage and rely entirely on chemical defences and camouflage to survive. Look for two main types across the reefs. Dorid nudibranchs feature a plume of gills around their rear. Aeolid nudibranchs grow finger-like projections called cerata down their backs. These projections store stinging cells stolen from their prey. Their bright neon patterns warn predators about their toxicity. Some species blend completely into the sponges they eat. Local genera include Chromodoris, Hypselodoris, Nembrotha, Phyllidia, Glossodoris, Thecacera and Flabellina. All of these animals are simultaneous hermaphrodites. Every individual possesses both male and female reproductive organs. Having both gives them more chances to breed during rare encounters on the reef. The World Register of Marine Species officially validates the taxonomy of the specimens recorded in Sabah.

The triangle between Mabul, Kapalai and Sipadan holds a huge variety of sea slugs. The sheer biomass of macro life here is huge. They are found on almost every substrate. They live on coral rubble and on discarded artificial debris under the Seaventures rig. You can spot them at Mel's Rock near Lankayan. They are regularly found in Darvel Bay around Tabawan Island. Their distribution depends entirely on their food source. They are highly specialised feeders. Some eat only a single species of sponge. Others feed on hydroids, bryozoans or tunicates. Nembrotha kubaryana feeds exclusively on tunicates. When you locate the specific food source you will often find the nudibranch. The dive guides understand these micro-habitats thoroughly. The Sea Slug Forum holds extensive photographic records from the region.

The top fifteen most-recorded nudibranch species in Semporna:

Hexabranchus sanguineus is a giant among sea slugs. It can grow to a massive size. You will often find it resting on the reef during the day. It looks like a mottled red lump. If disturbed it unrolls its bright red mantle margins and swims into the water column. It undulates its body gracefully. Sometimes a pair of commensal imperial shrimp rides on its back. These tiny shrimp stay attached even while the host swims. Look for its distinctive egg ribbons on the reef too. These look like delicate red roses attached to the rock. You must never pick up or unroll a Spanish dancer to make it swim. This is the most common abuse of this animal. The action causes severe physiological stress. You should let it sit quietly on the reef. Encountering a swimming Spanish dancer on a night dive remains a major highlight for visiting divers.

These animals move slowly but their lives are full of activity. You can watch for mating pairs. Two individuals align their right sides to exchange sperm. Look for them feeding on sponges. Pteraeolidia ianthina is known as the solar-powered aeolid. It houses symbiotic algae inside its body. It uses the sun to produce energy. Paradoris liturata is a clever mimic. It copies the appearance of toxic Phyllidiella nudibranchs to avoid predation. You may spot them laying egg ribbons in intricate spiral patterns. Be sure to check the surrounding area when you spot an egg mass. The adult is usually nearby. Some species store toxins from their food to deter fish. They do not pose a danger to divers.

Night dives offer an excellent chance to see active species. The Spanish dancer is primarily nocturnal. Most island resorts run night dives from their jetties. You can search the house reefs after dark to find animals that hide during the day. The guides use focus lights to scan the coral rubble and the sand. A night dive in Semporna often reveals rare hunting behaviours. The night diving page explains how to arrange dives after dark across the different island resorts.

Nudibranchs are excellent subjects for underwater photography. They move slowly and stay in one place. Pay close attention to the sensory horns and the plume of gills when framing your photograph. Focus on the sensory horns, called rhinophores, to draw the viewer into the picture. A macro lens is the usual choice. A 60mm lens works well for large dorids. A 105mm lens paired with a super-macro diopter suits tiny aeolids. You must position your strobes carefully. Side-lighting helps avoid overexposing their highly reflective skin. Black backgrounds make their neon colours stand out. You achieve this by using high shutter speeds and small apertures. A dedicated underwater photography package gives you the right boat support and specialised guides. The guides understand the specific angles required for a clean shot.

The rule is strict. You must never move an animal out of its host or habitat for a photograph. You should never prod or unearth or handle anything. A subject moved from its camouflage is exposed to immediate fatal predation. The true skill in macro diving lies in mastering neutral buoyancy and lighting and patience. You need to hover over the sand without stirring the silt. Let the guides point them out. They have trained eyes. They spot tiny subjects you would swim straight past. Your only job is to control your breathing and take the shot. Good buoyancy prevents accidental damage to the delicate coral structures these animals rely on.

The fragile ecosystems supporting these specialised creatures are easily disrupted. Darvel Bay faces localised threats from marine litter. Plastic bags and abandoned fishing nets impact the reefs at Triangle Reef and Baik and Sakar. The scientific literature confirms the danger of handling marine life. Touching a nudibranch removes its protective mucus layer. This exposes it to parasites and infections. You protect them by leaving them as you found them. The Semporna marine parks rely on divers to follow good ethical practices. Dedicated operators run regular reef clean-ups to remove debris and protect the benthic habitats.

Froggy Lair

Skill level: All levels Froggy Lair off Mabul is an excellent muck diving spot. You will find artificial structures on the sand. Nudibranchs coat the discarded debris. It offers calm conditions and a high concentration of macro subjects.

Paradise 1

Skill level: All levels This site features a shallow slope filled with coral rubble. Guides routinely point out 10 or 20 species in a single hour. It is highly reliable for macro subjects and offers gentle currents.

Mandarin Valley

Skill level: All levels Visibility here is often better than at Mabul. The slope holds abundant macro life. It is located just off the Kapalai sandbank. You can dive this site via Kapalai packages.

Mabul House Reef

Skill level: All levels The Mabul House Reef sits in front of the resorts. It offers excellent night diving opportunities to find nocturnal species. You access it straight from the jetty.

Kapalai House Reef

Skill level: All levels | Depth: 5–18 m The Kapalai House Reef sits under the resort walkway. You can dive it unlimited times during the day. The shallow depth gives you plenty of bottom time to hunt for tiny subjects.

You can reach these sites from Mabul and Kapalai. The Macro and muck packages put you where you need to be.

• Explore the Critters of Semporna to see what else lives in the muck.
• Read about finding Frogfish on the same reefs.
• Learn how to spot the Blue-ringed octopus.
• Find out more about Night diving across the islands.
• See the accommodation options in Mabul.
• Browse the Macro & Muck itineraries.

Send your travel dates alongside party details and your certification levels. The team comes back with what can be arranged for your group. You review the options before booking.