Following on from the series, here is my “Mucky Secrets" documentary in full. It’s a nature documentary about the marine life of the Lembeh Strait at the heart of the Coral Triangle off north Sulawesi in Indonesia. The Lembeh Strait is a popular scuba diving destination, famed for its excellent "muck diving". A huge diversity of weird and wonderful marine creatures can be found on the mucky seabed, including everything from tropical fish to benthic sharks to nudibranchs. Critters compete for survival with an armoury including camouflage, mimicry, toxicity, and dazzling coloration.

"Mucky Secrets" is an excellent resource for scuba divers, aquarists, marine biology students and anybody interested in the underwater world. The documentary features underwater macro footage from many of Lembeh’s famous dive sites including Critter Hunt, Police Pier, Tanjung Kusu-Kusu, Nudi Falls, Aer Perang, Jahir, Makawide, Nudi Retreat, Retak Larry, TK (Teluk Kembahu), Hairball and Aw Shucks.

Marine life featured in the film:

0:00:00 Introduction
0:05:11 Corals
0:05:57 Tunicates - sea squirts - ascidians
0:06:37 Symbiosis - sea anemones - anemonefish (clownfish)

0:07:29 Commensal shrimps (partner shrimps)
0:09:12 Emperor shrimp
0:11:07 Mantis shrimps
0:12:34 Squat lobsters
0:13:27 Hermit crabs
0:14:26 True crabs
0:15:55 Sea Urchins

0:17:11 Blue spotted stingrays
0:18:15 Brownbanded bamboo shark

0:18:59 Snake eels
0:20:27 Moray eels
0:21:34 Ribbon eels

0:22:33 Cardinalfishes
0:24:43 Trumpetfish
0:25:58 Seahorses
0:27:06 Pygmy seahorse
0:28:30 Pipefishes
0:30:38 Ghost pipefishes
0:33:22 Shrimpfishes - razorfishes
0:33:58 Seamoths - short dragonfish
0:35:03 Oriental flying gurnard
0:35:58 Blennies
0:36:49 Gobies
0:37:46 Sea pen
0:38:17 Dragonets
0:40:49 Mandarinfish
0:42:08 Frogfishes
0:46:39 Juvenile fishes
0:47:12 Spotted parrotfish
0:48:20 Sweetlips
0:49:05 Yellowblotch razorfish
0:49:37 Filefishes
0:50:24 Boxfishes - cowfishes
0:50:57 Puffers (pufferfish)
0:52:21 Sharpnose puffers (tobies)
0:52:50 Porcupinefishes
0:53:45 Panther grouper
0:54:10 Whitemargin stargazer
0:54:54 Leopard flounder
0:55:25 Flatheads
0:56:36 Scorpionfishes
0:57:27 Ambon Scorpionfish
0:58:04 Rhinopias
0:59:50 Lionfishes
1:02:29 Demon stinger (spiny devilfish, bearded ghoul)
1:03:17 Fireworm
1:03:45 Waspfishes

1:05:48 Cuttlefishes
1:08:38 Octopuses
1:11:34 Flame scallop
1:12:03 Sea snails
1:14:37 Sea slugs - nudibranchs
1:21:49 Sea slugs feeding
1:23:57 Nudibranchs mating
1:26:11 Sap-sucking slug
1:26:59 Headshield slugs
1:27:49 Sea hares
1:30:21 Polyclad flatworm
1:31:18 End credits

Part 20, the final part of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

The sap-sucking slug (Sacoglossa, sacoglossan) Elysia sp. is not a nudibranch. It does not have gills as such but breathes through two leafy flaps called parapodia that run most of the length of its body. The rhinophores on its head have a semi-tubular form. It feeds by sucking the fluid from green algae, and the chloroplasts it contains give the body a bright green colour which fades if the slug goes short of food. Behind the rhinophores it has tiny photo-receptors for eyes. The white spots are raised glands that can secrete a repellent white substance.

Headshield slugs (family Aglajidae, superfamily Philinoidea, clade Cephalaspidea) lack tentacles and most retain a small thin internal shell. They also have parapodia, which are wrapped up and around the body. Many excrete mucous to help them burrow into the substrate, and the headshield prevents sand entering the mantle cavity. The Gardiner’s headshield slug (Philinopsis gardineri) feeds on polychaete worms. And the pleasant headshield slug (Chelidonura amoena) feeds exclusively on acoel flatworms that infest hard corals and sponges. Small, dark eyespots on the front of its head give it very primitive vision.

Like the striated frogfish, the ragged sea hare (Bursatella leachii) is camouflaged with long papillae that help it disappear on a seabed strewn with algae. Sea hares (family Aplysiidae, superfamily Aplysioidea, clade Aplysiomorpha) get their name from the overall body shape and the long pair of rhinophores on the head, which are tubular, and give it an acute sense of smell. It also has a second pair of tentacles at the sides of the mouth and it gobbles up the thin layer of cyanobacteria that coats the seabed. Below the rhinophores it has a pair of tiny eyes. If it is disturbed it can release a noxious mixture of white opaline and purple ink. Recent research has shown that this sticks to the antennae of predators such as lobsters and dulls their senses. The bright blue eyespots covering the body are more vivid here than in populations in other parts of the world.

Ragged sea hares and the similar but smaller long-tailed sea hare (Stylocheilus longicauda) sometimes form huge swarming aggregations comprising hundreds or even thousands of individuals of varying size. They tumble over each other, devouring cyanobacteria and defecating as they stampede across the sea floor. In an aggregation they are an easy target for predators. Pufferfishes and predatory sea slugs have been seen to pick them off one by one. They breed quickly and have even been sold into the aquarium trade as “sea bunnies” for eating unwanted algae and providing food for other tank inhabitants with their larvae. It is said that inhabitants of some of the Cook Islands and Austral Islands collect and eat swarms of these sea hares, discarding the toxic internal organs. It is a mystery why sea hares aggregate like this. They have been observed to all mate, spawn and die at the same time.

Although they resemble sea slugs, polyclad flatworms (Polycladida) are quite different. The ruffled periphery of the glorious flatworm, Pseudobiceros gloriosus, forms a pair of pseudotentacles reminiscent of nudibranchs’ rhinophores. Occasionally flatworms leave the seabed to swim and when they do, they are a spectacular sight.

Part 19 of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

In this video we study how sea slugs (including nudibranchs) feed and mate.

All known nudibranchs are carnivores. The biggest family of nudibranchs, the chromodoridids, feed exclusively on sponges.

Most sea slugs have a ribbon-like tongue covered in microscopic teeth called a radula to help them consume their prey. The form of the radula varies greatly and is important as a basis for taxonomic classification.

We see a pleurobranch, Pleurobranchus forskalii, a different type of sea slug, feeding on an ascidian, or “sea squirt”, a type of tunicate.

Nembrotha nudibranchs also feed on ascidians. We see a Nembrotha lineolata feeding on a blue club tunicate. The ascidian feeds by filtering plankton from the water with its delicate, blue, sieve-like interior enclosed in a clear outer sac, its tunic. The sea slug everts its proboscis, its oral tube, out of its mouth and, with ruthless efficiency, sucks this fleshy interior right through the tunic. The radula teeth enable the slug to deal with the tougher parts of the sea squirt’s intestines.

Most sea slugs are quite specific in their choice of food, and so they are often drawn towards the same place. This increases the chances of encountering others of the same species and finding a mate. As they have no vision, nudibranchs locate each other initially through smell then touch.

During copulation, they line up their genitals which are on the right side of their body. All sea slugs are hermaphrodites and contain both male and female reproductive systems. During mating, each nudibranch receives sperm from the other.

We see a pair of Nembrotha purpureolineata nudibranchs mating. The penis, which is off to the side, is covered in tiny, sharp barbs which lock it into the vagina, which is at the centre of the stalk. The male organs often mature before the female ones. Small nudibranchs with an immature female reproductive system can store the sperm they receive until they start producing fertile eggs.

We also encounter a mating pair of Hypselodoris bullocki nudibranchs. Their genitals are also covered in tiny spines that anchor them together during copulation.

After fertilisation, a mucus-bound ribbon of eggs is laid in a spiral, often on or near the species’ food source. Most egg masses are toxic to predators and are abandoned by the parent.

Hypselodorid nudibranchs often follow each other around, top to tail. The reason for this ‘trailing’, or “tailgating” behaviour is a mystery. It’s thought to be a prelude to mating, but in some cases the trailing slug might simply be getting an easy ride in the search for food.

Part 18 of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

A huge and fascinating diversity of sea slugs, or opisthobranchs (Opisthobranchia), are found in the Lembeh Strait. Opisthobranch means “gills behind”, because their gills are located behind their heart.

Most sea slugs have all but lost their protective shell, but compensate with more advanced weapons of defence.

Over six thousand different species of sea slug are nudibranchs (Nudibranchia). The name means “naked gills”, referring to the rosette of branchial plumes on their back, surrounding their anus. These gills vary greatly in form, but all have a large surface area for oxygen exchange.

Part 17 of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

As we continue to examine molluscs (mollusks, Mollusca)  in this documentary series, we take a quick look at the electric flame scallop (Ctenoides ales), otherwise known as the “disco clam”, “fire clam” or “electric clam”. The flame scallop is a type of bivalve (Bivalvia). It appears to emit luminescent electrical pulses, but actually it is rolling and unrolling the edges of its mantle, revealing special particles that simply reflect light. The display is thought to attract phytoplankton as food and perhaps frighten off predators like crabs and shrimps.

We then turn our attention to sea snail (gastropods, Gastropoda). The grey bonnet (Phalium glaucum) is a typical sea snail. It has a protective, coiled shell that it can withdraw its entire body into. It glides over the substrate on its large, muscular foot, and at the rear we see the operculum, a hard lid that is used to close the opening of the shell after the snail withdraws into it. Two simple eyes peer out from under the front of the shell, and important sensory feedback also comes from the two tentacles. To one side is the inhalent siphon, a tube that the sea snail uses to draw in water for respiration.

The anatomy of another gastropod, the vomer conch (Euprotomus vomer), is different. Its mouth is much more obvious, at the end of a long protrusion called a proboscis. It is strictly a herbivore, and it uses the proboscis for locating and eating algae growing in the sand. It’s eyes are much more prominent too, at the end of long stalks, and jutting out from these stalks are two highly sensitive tentacles. Rather than gliding, it uses its operculum to drag itself along the bottom in a lurching motion.

Conchs are a popular food, and their shells have symbolic and religious significance in some cultures. They have been used for everything from musical instruments, to weapons, to ink holders.

We then encounter a whitespotted hermit crab inhabiting an empty cone shell. The main sensory device of cones like the ivory cone (Conus eburneus) is the siphon itself which contains highly sensitive chemoreceptors. If it detects suitable prey the cone will unleash a harpoon from its proboscis containing a highly venomous neurotoxin, powerful enough to kill humans.

Part 16 of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

In this video I look at cuttlefishes (Sepiida) and octopuses (Octopoda); types of cephalopod (Cephalopoda) found in the Lembeh Strait.

The broadclub cuttlefish (Sepia latimanus) is the second largest species of cuttlefish, and the most common on coral reefs. It can adopt an infinite number of textures, colours and poses to camouflage itself, communicate and to hypnotize prey.

As the name suggests, the crinoid cuttlefish (Sepia sp.) tends to hang around feather stars. We find one hiding amongst the branches of a decaying staghorn coral. This is an undescribed species known only from Indonesia, and recognised by the dark spots at the front of its lower arms.

The dwarf cuttlefish, or stumpy-spined cuttlefish (Sepia bandensis) is a tiny species that is usually only seen at night. Rather than swimming, it usually uses its lower arms to walk on and explore the seabed. It is often found in association with echinoderms such as sea urchins.

Another species that walks on its arms is one of the real stars of Lembeh, the flamboyant cuttlefish (Metasepia pfefferi). When disturbed it abandons its camouflage and the skin adopts spectacular shades of purple and yellow, with waves of white radiating down the mantle. The colour changes are achieved by adjusting millions of pigmented cells in the skin called chromatophores. This is an example of aposematic coloration whereby a creature warns potential predators of its toxicity. Scientists have recently discovered that the flamboyant cuttlefish’s muscle tissue contains a unique and highly potent toxin, proving that this display is no bluff.

We see an adult flamboyant cuttlefish using its special feeding tentacles to snatch prey such as small shrimps and gobes, and a tiny juvenile raising its median tentacles, a common threat display amongst cuttlefishes.

Cuttlefishes’ intelligence and unique powers compensate for their lack of a protective shell. They have the highest brain-to-body-mass ratio of all invertebrates, and researchers have shown them to possess a good memory and a high capacity for learning.

Octopuses are closely related to cuttlefishes and have similar characteristics and intelligence.

At TK we encounter an undescribed octopus, a near relative of the mimic octopus and wonderpus, retreating to its burrow with a captured crab. The octopus usually injects the crab with a paralysing saliva before using it’s parrot-like beak at the centre its arms to excavate the meat from the crab.

Finally on a night dive at Aer Perang we encounter a starry night octopus, Callistoctopus luteus, twisting and turning around the reef as it tries to escape my attention.

Part 15 of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

One fish that divers should be wary of in the Lembeh Strait is the demon stinger (Inimicus didactylus) as its sting is extremely painful and can be deadly to humans. They have excellent camouflage and often lie partially buried in the muck. These fish are more closely related to the lethal stonefish than to scorpionfishes, and are known by a multitude of other evocative common names including spiny devilfish, bearded ghoul and sea goblin.

The lower two rays of the pectoral fins are detached from the fin, and the demon stinger walks on them in a manner similar to some dragonets.

Demon stingers have no known predators. Many fellow bottom dwellers are oblivious to their existence. We see a fireworm (Chloeia parva) a type of bristleworm, crawling right over the top of a well-camouflaged demon stinger.

Like their scorpionfish relatives, waspfishes (family Tetrarogidae) are also armed with venomous spines in their dorsal fin. We see another type of polychaete worm wriggling past a wispy waspfish (Paracentropogon longispinis). The wispy waspfish’s coloration is variable.

Bandtail waspfishes (Paracentropogon zonatus) are sometimes found too, and the whiteface waspfish (Richardsonichthys leucogaster) is one of the more common types.

With its spines erect, like its namesake’s crest, the cockatoo waspfish (Ablabys taenianotus) sways from side to side, mimicking a dead leaf in surge. They are sometimes found in pairs on the open seabed.

Part 14 of my documentary, “Mucky Secrets”, about the fascinating marine creatures of the Lembeh Strait in Indonesia.

There are many species of scorpionfish in the Lembeh Strait, and it is often impossible to accurately identify them from pictures alone due to the minor differences in their anatomy and the highly variable nature of their camouflage. All scorpionfishes possess venomous spines on the dorsal and anal fins for self-defence, and for stunning their prey. They can also deliver a painful, sometimes even deadly sting to humans. The sting can be deactivated and the pain alleviated with prolonged immersion in hot water.

We first meet a flasher scorpionfish, Scorpaenopsis macrochir, at Aer Perang. Like so many cryptic Lembeh creatures, scorpionfishes are ambush predators, using camouflage to remain hidden, then pouncing on unsuspecting prey when it passes.

One of the best camouflaged is the Ambon scorpionfish, Pteroidichthys amboinensis, named after the island to the south east in the Maluku islands. It has very long protrusions, particularly above its eyes. Due to its sedentary lifestyle, the Ambon scorpionfish gathers a lot of algae on its body which helps it disappear into the surrounding territory. Like many scorpionfishes it cleans itself by occasionally shedding the outer layer of its skin, known as the cuticle.

The scorpionfish of the Rhinopias genus are fantastic and rare creatures, and considered by many to be the holy grail of muck diving finds. The Eschmeyer’s scorpionfish, Rhinopias eschmeyeri, sometimes known as a “paddle flap scorpionfish”, is occasionally found. We encounter a pink specimen at Aer Perang.

The weedy scorpionfish, Rhinopias frondosa, typically bears a spotted coloration and more skin filaments than the Eschmeyer’s scorpionfish. We meet one also at Aer Perang.

Lionfishes are close relatives of scorpionfishes. Rather than camouflage, they bear a bold warning pattern to advertise their toxicity and confuse predators. Like scorpionfishes, they have venomous spines along their dorsal fin, but the venom glands are smaller, so their sting is generally less potent. Human fatalities are very rare.

The dwarf lionfish, Dendrochirus brachypterus, also known as a “shortfin turkeyfish”, splays its dorsal rays to maximise its defences. It feeds mainly on crabs at night. The male can be identified by its larger head and longer pectoral fins with more bands than those of its female partner.

Red lionfish, Pterois volitans, are sometimes seen too. We encounter is a young red lionfish at Aer Perang, and a mature adult at Jahir. They have tentacles above the eyes, and some exhibit globular fleshy growths beneath these tentacles.

Although indigenous only to the Indo-Pacific, red lionfish have been introduced to the east coast of the United States and spread all the way from North Carolina down to the Caribbean. With few natural predators and a voracious appetite for smaller reef fishes, the population has expanded exponentially, wiping out many native species and greatly upsetting the balance of reef ecosystems. Scientists are trying to understand why the native indo-pacific population is not out of control, in an effort to find solutions to the west-Atlantic invasion.

Part 13 of my documentary, “Mucky Secrets”, about the marine life of the Lembeh Strait in Indonesia.

After a quick look at the panther grouper, Cromileptes altivelis, also known as the humpback grouper or barramundi cod, I explore demersal fishes, those that live on or near the seabed. Of these, benthic fishes actually rest on the sea floor.

The whitemargin stargazer, Uranoscopus sulphureus, spends most of its time buried in the substrate, with only its upper, or dorsal, surface exposed, where its eyes and mouth are located. Like frogfishes, stargazers are ambush predators. They have a worm-like lure that extends from the upturned mouth to attract fish that pass overhead. Stargazers are also equipped with poisonous spines at the rear of the operculum, the gill cover. The papillae fringing the mouth help stop sand from falling in when the fish is buried.

The leopard flounder, Bothus pantherinus, has adapted to life on the bottom with a superb camouflage. Such lefteye flounders are symmetrical and swim upright like other fishes when young. As they develop, the eye on the right side migrates to the left, thus enabling them to lie flat on the bottom. Their eye stalks can be retracted for protection, but enhance their view when extended.

Flatheads also have excellent camouflage and a stealthy, low profile, but unlike flounders, they are dorsally compressed and remain symmetrical. They are also ambush predators, and often hide by burying much of their body in the substrate. Flatheads are related to scorpionfishes and have short, venomous spines on top of their head.

We meet a Japanese flathead (Inegocia japonica), a black-banded flathead (Rogadius patriciae), and finally a pair of spiny flatheads (Onigocia spinosa) at Retak Larry, a classic, dark sand muck diving site named after the late Lembeh pioneer, Larry Smith.

Part 12 of my documentary, “Mucky Secrets”, about the marine life of the Lembeh Strait in Indonesia.

In this video I look at fishes in the order Tetraodontiformes. First of all we encounter a very young boxfish, possibly a longhorn cowfish, Lactoria cornuta. Along with toxic skin, the boxfish’s main defence is a very hard carapace of bony plates. The juvenile’s coloration helps it remain unnoticed while the body hardens.

Next is a juvenile thornback cowfish, Lactoria fornasini, sheltering in Halimeda algae. Juvenile boxfishes and pufferfishes often tuck their tail to one side when it is not needed for swimming.

Next we meet a juvenile starry puffer, Arothron stellatus, and its dramatically different adult counterpart.

Although puffers are slow movers, the tail can give them a great turn of speed when threatened. As a further defence, puffers can inflate their bodies with water, vastly increasing their size and revealing short, sharp spines on their skin.

They are believed to be the second most poisonous vertebrate on earth, after the golden poison frog. However some predators can tolerate the toxin, and some parts of them are carefully prepared as a delicacy in Japan, Korea and China.

The juvenile guineafowl puffer, Arothron meleagris, has a black and yellow coloration that advertises its toxicity to potential predators. This is a common combination of warning colors in the animal kingdom.

More elongate puffers are found in the Lembeh Strait too. We encounter a narrow-lined puffer, Arothron manilensis, at Hairball and a shortfin puffer, Torquigener brevipinnis, at TK.

Sharpnose puffers, also known as tobies, have elongated snouts and slimmer bodies. We meet at a Valentini puffer, Canthigaster valentini, a Bennett’s sharpnose puffer, Canthigaster bennetti, and a compressed toby, Canthigaster compressa.

The birdbeak burrfish, Cyclichthys orbicularis, is a type of porcupinefish. It is covered in spines which are permanently erect, and it can inflate its body like puffers. It’s eyes contain iridescent green specks.

Conversely, the spines of the long-spine porcupinefish, Diodon holocanthus, lie flat against its body when not it is not inflated.

Finally we encounter a long-spine porcupinefish sharing its home with a small birdbeak burrfish.