Sadc Creature Feature

Getting to Know... Manta Rays Manta Ray Manta birostris Width: up to 6.7 m, possibly up to 9 m Depth: to 40 m The Manta Ray is the largest ray in the ocean; individuals with a wingspan (disc width) of 4 m are relatively common. Mantas were once believed to be dangerous, but are in fact completely harmless plankton feeders. They feed by swimming with their enormous mouths wide open, using the fleshy extensions on either side—called cephalic fins—to channel the plankton-rich water towards their mouths. The water is sieved through the gill rakers, trapping the tiny plankton. The Manta Ray has one dorsal fin and a relatively short, whip-like tail that lacks a sting. It’s back is grey-blue, often with pale grey markings across the shoulder region. The underside is white with grey spots. Like Whale Sharks, Manta Rays have unique spot patterns that can be used to identify individual rays. Although Mantas are usually seen swimming slowly and gracefully over the reef, they can move extremely fast, even launching themselves out of the water and landing on the surface with a loud slap. This is believed to help remove parasites. Where to See: South Ari’s Manta Point is one of the most famous dive sites in the Maldives. During the NorthEast Monsoon, Mantas circle over cleaning stations on the reef top to have parasites and dead skin cells picked off their bodies by cleaner wrasses.

Getting to Know... Smallscale Scorpionfish Smallscale Scorpionfish (Flathead Scorpionfish, Tasseled Scorpionfish) Scorpaenopsis oxycephala Length: up to 35 cm Depth: 1-35 m The Smallscale Scorpionfish is actually the largest scorpionfish in the Maldives. The common name refers not to its overall size but to the small scales covering its body. Widespread in the Indo-Pacific, it inhabits reef slopes and channels with mixed rock and coral bottoms. The Smallscale Scorpionfish is a master of disguise, its mottled skin making it nearly indistinguishable from the reef as it lies motionless waiting for its prey of small fishes to pass by. It makes rapid colour changes, adapting itself to the colours of the surrounding corals. Adults are “bearded” with fleshy tassels helping them blend into the reef. Like all members of the scorpionfish family, the Smallscale Scorpionfish has venomous dorsal fin spines. It is not overtly aggressive; it erects its dorsal spines when threatened but will usually flee a short distance then freeze, merging into the the background. Poison is produced by skin cells that cover the grooves running the length of each dorsal spine. The protein-based venom is unstable at high temperatures and is broken down by soaking the affected area in hot water. Where to See: Smallscale Scorpionfish are common throughout South Ari Atoll, but especially so at Bama Thila, Kahambu Thila, Mirihi Medu Thila, Madivaru Thila and Mas Thila.

Getting to Know... Dogtooth Tuna Dogtooth Tuna Gymnosarda unicolor Length: to 1.6 m Depth: 3-100 m The Dogtooth Tuna is a large, fast fish common along deep outer reef walls. It is widespread throughout the Indo-Pacific. Along with the Giant Trevally, Napoleon Wrasse and large groupers, the Dogtooth Tuna is one of the apex non-pelagic predators of its range. It can be curious about divers, sometimes making close passes. The Dogtooth Tuna is a near-shore fish, with smaller individuals hunting in shallow reef areas and larger ones patrolling deep reef drop-offs. It feeds on small pelagic fish and any reef fish that venture too far off the reef, and will readily attack any fish that fits in its mouth. Not a true tuna, the Dogtooth is closely related to the bonitos, with the large teeth and straight-edged first dorsal fin characteristic of bonitos. It has two separate dorsal fins, followed by seven finlets. It has a large mouth with conical teeth, and the rear half of the lateral line is wavy. With its brilliant blue or black back and silvery belly, the Dogtooth Tuna uses counter-shading to help it blend in with the water whether it is seen from above or below. This helps it to hide from both prey and predators. Where to See: You’ll find Dogtooth Tuna patrolling the current-facing side of most reefs. Angaga Thila, Kahambu Thila and Haluvaa Thila are especially good for spotting Dogtooths, as is Madivaru with an incoming current (reef on the right shoulder).

Getting to Know... Honeycomb Morays Honeycomb Moray (Giraffe Moray, Blackspotted Moray) Gymnothorax favagineus Length: up to 2 m Depth: 1-50 m The Honeycomb Moray is one of the most photogenic animals on the reef, it’s yellowish skin covered with black blotches forming a distinctive honeycomb pattern. Individuals found on clear coral reefs usually have proportionately less black than those found in turbid waters. The Honeycomb Moray is one of the largest morays in our area. Like most morays, it hunts mainly at night, preying on smaller reef fishes. Honeycomb Morays are quite timid and safe to approach as long as they are not provoked. As with all morays, feeding or stroking them could result in serious injury and should be avoided. There are an estimated 170 species of moray worldwide. Of these, 40 have been recorded from the Maldives, though most are secretive and rarely seen. Their bodies are nearly all muscle and they are extremely strong. With their powerful jaws they can attack larger creatures, ripping flesh by twisting their bodies. Where to See: There are at least three Honeycomb Morays living on the south side of Kudarah Thila, though they rarely all make an appearance at the same time. There are two Honeycombs on the reef wall at Rangali Outside, north of the main coral block. They can also sometimes be found on the reef-top at Madivaru.

Getting to Know... Nudibranchs of M/V Kudhimaa There are several species of nudibranchs on the wreck of the M/V Kudhimaa, but they are likely all of the genus Tambja, of which there are around 30 different species worldwide. Differences between nudibranch genuses are based mainly on internal anatomy, particularly the mouth structures and reproductive systems. One key external characteristic for this genus is the flattened oral tentacles. Tambja olivaria Probably found throughout the IndoWest Pacific, this nudibranch is the most common on the Kudhimaa and is found feeding on byrozoans. It has a dull olive-green background with black and orange markings. The rhinophore clubs (horns) are black. The gills are yellow on the outer face and black on the inside. This animal grows to at least 90 mm in length. If touched, it oozes green pigment that burns like acid. The close-up at left very clearly shows the flattened oral tentacles at the base of the head, characteristic of all Tambjas. The photo also shows a dark patch below the right rhinophore. This nerverich pit is thought to be a chemosensory organ used in finding the byrozoans (small, coral-like colonial animals) that all Tambjas feed on. The small yellow nudis found in great numbers on the wreck are likely juveniles of T. olivaria, though it is possible that they are a separate species altogether. There are usually several mid-ship on the port-side face of the box housing the crane engine.

Getting to Know... Nudibranchs of M/V Kudhimaa Tambja affinis Known from the western Indian Ocean and Thailand, this species grows to at least 70 mm in length.The background color is light blue or green to dark black, with wide yellow to bluegreen longitudinal bands. The edge of the foot has a yellow band. The outside of the gills is yellow and the pinnae (feathery branches at the ends of the gills) are a dark purplish black. This species is very similar to several other Tambjas. One key to identification is the milky blue-green patch between the rhinopores, along with several similarly coloured patches at the base of the gills. The individual in this photo can be seen feeding on the arborescent (plant-like) byrozoans that are the food of all Tambjas. Tambja morosa Though uncommon in South Ari Atoll, this species is found throughout the tropical WestPacific. It is a large Tambja, growing to about 70 mm long. Elsewhere in its range it is typically reported as black with blue markings; this lighter blue animal is simply another colour form.

Getting to Know... Common Reef Octopus Common Reef Octopus (Big Red Octopus, Day Octopus) Octopus cyanea Length: up to 80 cm Depth: up to 30 m The Common Reef Octopus is one of the most common octopuses throughout the Indo-Pacific. It is usually purplish-brown but can rapidly change color and texture. Unlike other octopuses, it feeds during the day, preying mainly on bivalves and crustaceans. The Reef Octopus is a master of camouflage. It has millions of pigment cells, called chromatophores, in its skin; each one is surrounded by muscles that contract or relax to change how the pigment is displayed. A newly hatched octopus may have only a hundred or so chromatophores, but adults can have over a million. This allows the octopus to change colours instantly as it moves over the reef, matching the colors and textures of its surroundings. The Common Reef Octopus is shy and usually retreats into its reef hideaway—marked by empty shells left-over from meals—when approached. Juveniles live less secretively in shallower waters. Octopus are often seen mating on the reef. The male extends one of its tentacles, the specialised hectocotylus, to transfer sperm to the female. Males live only a few months after mating; females do not eat while tending their eggs and die shortly after they hatch. Where to See: Octopuses can be found just about anywhere. Once spotted, approach slowly and stay a few metres back to avoid frightening it into the reef.

Getting to Know... Bruun’s Cleaner Shrimp Bruun’s Cleaner Shrimp Urocaridella antonbruunii Length: up to 3 cm Depth: to 30 m The nearly transparent Bruun’s Cleaner Shrimp has red and white bands on the carapace (head section) and legs, and a long rostrum (horn between the eyes). It is an important invertebrate cleaner of a variety of reef fishes, including moray eels and groupers, and can be found in holes and under ledges along reefs throughout the Indo-West Pacific. Bruun’s Cleaner Shrimp generally live in groups, waiting inside their cleaning stations for clients to pass by. “Cleaner shrimp” is a generic term for any swimming decapod (tenfooted) crustacean that cleans other organisms of parasites. In this widely-used example of symbiosis, the fish benefit by having parasites and dead skin or scales removed, and the shrimp get an easy meal. Bruun’s Cleaner Shrimp are easily approached and divers with the patience to keep still while extending a hand into a cleaning station will be rewarded with a shrimpmanicure. For the more daring, they also do teethcleaning. Where to See: Bruun’s Cleaner Shrimp are common inside overhangs and under ledges on nearly every dive site in the atoll. Take a torch with you to make them easier to spot.

Getting to Know... Spotted Porcelain Crabs Spotted Porcelain Crab (Anemone Porcelain Crab) Neopetrolisthes maculatus Length: up to 3.5 cm Depth: to 25 m Living with sea anemones, the Spotted Porcelain Crab is creamy white with red to brown dots. It is found throughout the Indo-Pacific. The Spotted Porcelain Crab lives mainly on short-tentacled Stychodactyla anemones. Immune to its host’s stinging cells, or nematocysts, it can be found among the tentacles or hiding from predators underneath the anemone’s mantle. On a rising tide, the crab comes out of hiding to fish for the plankton it feeds on. It catches its meal by swinging its two maxillipeds (modified appendages) back and forth in the water in a rhythmic motion. The fanlike maxillipeds are edged with fine filaments that make a sieve, so the crab can scoop plankton out of the water. Spotted Porcelain Crabs occasionally moult their shells. Males must find a freshly-moulted female to mate with while the new shell is still soft. Females then carry the fertilized eggs on their bodies, beneath the abdominal flap, until the eggs hatch and the larvae join the water column as plankton. Where to See: Spotted Porcelain Crabs are common in short-tentacled anemones throughout the atoll, but are not always visible. Look carefully in any anemones you come across and you’re likely to encounter one or two.

Getting to Know... Flatworms Flatworms Phylum: Platyheminthes Class: Turbellaria Approximately 20 000 different species of flatworms have been identified worldwide. They are simple life forms, without respiratory or circulatory systems. The only body cavity is the opening to the gut, which lets food in and waste out. Flatworms have no gills, so oxygen absorption happens through the body wall.

Suzanne’s flatworm Pseudoceros suzzanae

Yellow Papillae flatworm Thysanozoan migropapillosum

Flatworms belong to the class that includes tapeworms, liver-flukes and other internal parasites. Though they are often mistaken for sea slugs (such as nudibranchs), which some mimic as a form of defence, they are not at all related.

Although very thin and delicate, flatworms are active carnivores and scavengers, feeding mainly on colonial animals like soft corals and bryozoans. Like sea slugs, some flatworms store the toxins they absorb from their food, making them distasteful or toxic to predators. By waving the fine, hairlike cilia covering their bodies, flatworms glide along the sea floor. When disturbed, they can swim by throwing the sides of their bodies into undulating waves. Flatworms are hermaphroditic. When they mate, they exchange sperm so both worms become fertilized.

Glorious flatworm Pseudobiceros gloriosus