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BY DOUGLAS DAVID SEIFERT 9 0
WATER COLUMN / 1 1 / 22/11/09 18:21:35 www.divemagazine.co.uk investigates the secret world of the Douglas Seifert , is the , moray and the timeless appeal it holds for coral reef divers Gymnothorax javanicus Every diver relishes a decent moray eel sighting, but there’s more to these but there’s Every diver relishes a decent moray eel sighting,
predators than meets the eye. predators than meets the eye. 5
2 the giant moray, the giant moray,
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C EEL APPEAL largest of the moray eels, shown here amid glassy sweepers shown here amid glassy eels, largest of the moray Atoll in the Maldives at Baa BIG DEAL: BIG DEAL: E D _ n m u l o C
r e t a WWater Column_DEC09.indd 25 FROM TIDAL pools formed at the lowest of low tides to fantastic and dangerous-looking teeth, has fascinated rocky habitats, wrecks, and reefs and down along coral people since the dawn of recorded history, with walls leading down to the abyss, wherever there is a narratives dating back to the time of the Roman Empire. suitable crevice, one is almost certain to find a moray eel Morays were said to be kept as pets or venerated as of one species or another. objects of curiosity, or, allegedly, as instruments of By day, they are shy and retiring, their bodies punishment or execution for slaves, criminals and concealed in labyrinthine lairs, with only their heads prisoners during the glory days of Roman civilization. peeking out from the rocky shadows towards open water. But the moray does not bare its open maw to display Their large, unblinking eyes stare fixedly and their jaws aggression – it is simply breathing. The eel’s gills are set open and close ceaselessly, rhythmically, displaying a well back from the mouth along its narrow flanks, hidden fierce array of multitudinous, backward-pointing, needle- beneath a narrow slit. In order for water to pass over sharp teeth set in long, tapered jaws. The sight of a those gills, the moray effectively gulps water by opening large aquatic creature peering out of a hole, with jaws its mouth wide and pumping the water through its gills. gaping wide and displaying a bear-trap mouth of Moray eels have a snake-like body but are bony fish,
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WATER COLUMN / 1 1 / 22/11/09 18:23:00 Rhinomuraena www.divemagazine.co.uk ) that is a hyperactive hunter by day, and relies ) that is a hyperactive hunter by day, In the darkness, poor vision is of little consequence Morays are endowed with other senses enabling them The moray eel’s dominant sensory apparatus is its Morays do not have scales, but instead a thick, smooth Morays do not have scales, with a The lubricating, protective mucus in conjunction The moray’s during the day is largely tendency to hide daytime These diminished senses would give potential quaesita on speed to ambush small fish prey – but most morays the with the fall of night, are daytime recluses. However, morays become active, prowling the reefs on a relentless hunt for prey. because, for the most part, fish and invertebrates see equally poorly at night. Morays vacate their lairs to openly poking probe the reef on a search-and-destroy mission, their noses in everything and everywhere. to succeed as one of the reef’s top predators. They possess a reduced lateral line system restricted to the head that is used to detect and analyse vibrations, pulses and movement. This effectively creates a three- dimensional picture of the immediate surroundings – and all fishy and invertebrate activities taking place within it. acute sense of smell: more than anything else, a moray eel could be considered a swimming nose. Their sense of smell is in a state of constant overdrive: a moray eel continuously monitors olfactory information by taking continuous band from just behind the head to and around the head to and around band from just behind continuous base of the anus. tail to terminate at the the tip of the vertebrate system is a bony spinal column, Their skeletal spinal chord but with flexible similar to human or snake cartilage of rigid bones. This anatomic ribs instead to bend and twist with fluid flexibility enables the moray contortease, with an ability to itself unmatched in the the octopus. enemy, sea except only by its arch is covered in a mucus slime (toxic in some This skin. barrier to disease, species) that forms a protective The mucus also servesinfection and parasites. to facilitating passage over rough lubricate the moray’s body, surfaces,and, in the case of through sand and rubble – sand-dwelling morays, to solidify grains into building sand even material and form the walls of tunnels. The mucus provides a kind of temporary the exposure suit to keep when it moray wet and lithe on the irregular occasions terrestrial obstacles and a crossing over land and makes of water briefly exits the ocean to move from one body the mucus covering is highly Additionally, to another. effective in making difficult a would-be predator’s purchase upon a writhing eel. extremely efficient form for an highly flexible body make in a of swimming called undulating. The eel moves as well as rippling motion that can propel it backwards forwards, fish species. a feat impossible for most other the result of its sensory A strengths and weaknesses. suited to identifying light moray’s eyesight is rather poor, It sees more motion than detail intensities but not colour. and not very well at that. Its hearing is rudimentary. predators such as sharks the advantage. Since the moray cannot see well, hiding is an obvious tactic. There are exceptions – such as the ribbon moray (
Gymnothorax ) is only found at dovii HAPPY FAMILIES: HAPPY FAMILIES: this unique aggregation of fine-spotted moray eels ( Malpelo Island in the Eastern Pacific , the , the true eels, Monopenchelys Muraenidae ), which can weigh in at 36kg. anguilliformes 7 2
d d ) at 20cm in length, to the giant moray n i . 9 Morays are found in all tropical and temperate seas Lacking pectoral fins, morays have dorsal and ventral 0 C Gymnothorax javanicus members of the family which contains more than 600 species in four suborders and 19 families. One of these is the family of the moray eels, comprising about 200 species of morays in 15 genera. and come in a variety of colour patterns and sizes, from the relatively small red-faced moray ( acuta ( There is also a freshwater moray eel that can be found in of the US. southeast Asia and in the Great Lakes fins fused with the caudal (tail) fin that run as a E D _ n m u l o C
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WWaterater CColumn_DEC09.inddolumn_DEC09.indd 2828 22/11/09/11/09 18:23:2818:23:28 in water from its surroundings, gathering waterborne GENDER BENDER: roof of their mouth to enhance gripping and crushing. scent molecules through its nostrils, via paired, tube-like a male (blue) ribbon One of the most extraordinary characteristics about eel (Rhinomuraena structures called nares. Water flows into anterior quaesita) transforming moray eels has only been recently discovered. The moray openings at the tip of their snout, scent molecules are into a female (yellow) eel possesses a raptorial second set of jaws deep within
at Lembeh Strait, WATER COLUMN differentiated and analysed as they flow through the Sulawesi, Indonesia its throat. Why do eels have two sets of jaws? All the olfactory organ before being expelled through the [opposite page]; the better to eat you with, my pretty… posterior nostril tubes situated above the eyes. The subtle blackcheek has proved The moray’s heads and body is narrow and to be more aggressive differences in intensities of scent between the two sets of than most moray eels compressed, so it cannot achieve the suction technique nares are evaluated and used to pinpoint the source of [below] other fish use to swallow prey. At best, a moray can the odour with an astonishing accuracy. bite and grab, and if the prey item is too large to swallow, As a top predator, the moray has a cosmopolitan diet the moray is in danger of asphyxiation because their consisting of crabs, shrimp, lobsters, fish and their throat will be blocked. Other fish, with a larger oral irresistible prey: the octopus. The greater the scent a prey cavity, use a volume of seawater to help suck the prey animal emits, the greater the chance the eel has to find it down their throats and in the process also pass water and devour it. For instance, parrotfish are well known to over their gills. A moray eel cannot do that because the secrete a mucus cocoon enveloping their entire bodies prey is a tight fit in its mouth, leaving no space for water when they retire under coralline structures at night: the to be entrapped and pass along. mucus membrane is designed to keep the parrotfish Instead, morays rely on a second set of jaws, called scent in so an eel does not detect the slumbering fish. ‘pharyngeal jaws’, to transport prey from the mouth Moray eels and octopus are eternal enemies: they vie down their gullet. Other bony fish also have pharyngeal for the same habitat; they pursue the same hunting jaws that assist in swallowing, but they are usually strategy as nocturnal hunters, and they consume the grinding plates or small teeth. A moray eel’s pharyngeal same prey. It seems only natural that their jaws are muscular and have sharp recurved competition should turn towards each other. teeth, allowing the jaws to be projected far When an eel is a juvenile, it may fall prey to WHY DO EELS HAVE forward where they act like forceps, gripping an octopus, but once it reaches a good size, then dragging the prey down the the tables are turned and the moray TWO SETS OF JAWS? oesophagus, where it can be swallowed and becomes the invertebrate’s most deadly foe. ALL THE BETTER TO EAT digested. This dual-jaw system – likened to Although an octopus has great strength in YOU WITH… the monster of Ridley Scott’s Alien film – its arms and gripping suckers, the soft flesh “ allows the moray to eat a wide variety of is no match for the needle-sharp teeth and oddly-shaped prey of varying sizes and to savage power of the moray’s jaws. The moray’s writhing, swallow them in spite of its compressed physiology. An muscular body, in its mucus covering, easily overcomes eel may bite off more than it can chew, but thanks to its the octopus’ attempts to grasp or deflect it. If an octopus pharyngeal jaws, not more than it can swallow. does not flee immediately, it is likely to lose an arm or Morays eels are generally solitary animals and can two, if not its life. ”exhibit a fierce territoriality. In some species, however, A moray may also utilize a technique known as and in some locations, individuals may tolerate others ‘knotting’, taking hold of its opponent with its jaws and of their own kind in a desirable cranny. At the remote forming a loop with its body, then pulling its head through Eastern Pacific island of Malpelo, a unique aggregation the loop, allowing the musculature of the body to act with of fine-spotted moray eels (Gymnothorax dovii) can be force against the object in its mouth and exert great found cohabitating the current-swept, boulders of the leverage. This technique is highly effective in pulling and rocky undersea topography. tearing the flesh of whatever is in the moray’s toothsome Although human beings have been attacked or bitten grasp. Some species also have a jagged set of pseudo- by moray eels, most species shy away from human teeth called ‘vomerines’ projecting downward from the contact. They really need to be provoked to bite, either by harassment or through accidents caused by attempts to feed the morays. The one exception that comes to mind: Gymnothorax breedeni, the blackcheek moray so common in the Maldives. They will come out of their holes – unprovoked, I swear it! – to nip the unwary diver; for this diver, the pesky blackcheek moray is the only eel that has lost its appeal. ■
• The den of fine-spotted moray eels was photographed at Isla Malpelo, Columbia, while Douglas was on board the MV Sea Hunter, and guided by the irrepressible Wilson, email: [email protected], web: www.underseahunter.com. Malpelo is the only known location where concentrations of this species of moray can be found so densely grouped together.
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