FEEDING STRATEGIES
When manta and devil rays open their mouths to feed, unfurling those hornlike projections, the cephalic fins, they transform into feeding machines. The once flattened body and mouth becomes a giant black hole, with the pectoral fins serving as wings that power the ray through the water.
To maximise their planktonic rewards for the energy they expend while feeding, mobulid rays have evolved a wide variety of feeding strategies. The overall feeding technique is simple. The manta swims through the water with its massive mouth agape, and the paddle-like cephalic (head) fins unfurl in front of the mouth to funnel plankton-rich water through their specially adapted gills. But variations in the rays’ swimming positions, and the strategies they use as a group, are key to their feeding success. These strategies can often be complex, requiring coordination among multiple individuals to enhance feeding efficiency. Only recently have scientists begun studying these techniques in depth, but to date, a total of eight different feeding strategies have already been described.
Straight Feeding
Each mobulid feeds independently, swimming horizontally forward in a straight line with its cephalic fins held open in front of the fully open mouth so that the fins almost touch in the centre. The rays perform a sharp 180 degree turn at the end of each 'feeding run', before commencing back along the same plane, feeding in the opposite direction.
Surface Feeding
Feeding independently, the manta ray positions itself just below the water's surface, tilting its head back so that the upper jaw of its mouth is just above the water. The close proximity to the surface means the manta has to reduce the up-stroke of the pectoral fin to prevent its fins from lifting above the water’s surface. The feeding runs also follow the same pattern as straight feeding, although in order to execute the 180 degree turn at the end of each run the manta is required to undertake a slight dip away from the water’s surface.
Chain Feeding
Lining up head-to-tail, the mantas or mobulas form a line of as many as several dozen individuals moving through the water column together along the horizontal plane. Mouth and cephalic fins are held in the same position as straight feeding and at the end of each feeding run the chain of rays often continue to hold the line which snakes around behind the leading animal. Similar to a flock of birds flying in a ‘V’ formation, the following rays often position themselves slightly above or below the individual in front of them.
Piggyback Feeding
Feeding together in close proximity, a smaller individual, usually a male manta, positions itself directly on the back of a straight feeding larger individual, usually a female, matching the beats of its pectoral fins to the beats of the larger individual. Occasionally several individuals piggyback on top of one manta, resulting in stacked feeding of three, or even four, manta rays all swimming horizontally through the water column together. At the end of a feeding run when the lowest positioned individual turns to swim back in the opposite direction, the piggybacked individual/s are usually displaced. Piggyback feeding has only been observed in reef manta rays (Mobula alfredi).
Somersault Feeding
Feeding individually the manta or mobula ray performs a tight backward somersault in the water. The ray completes a 360-degree loop in the water column, the diameter of which is less than the disc width of the animal’s body. As many as several dozen continuous backward somersaults may be performed before the animal breaks the looping cycle and returns to straight feeding.
Cyclone Feeding
This behaviour has only been recorded in reef manta rays (Mobula alfredi). A line of chain feeding mantas begin to loop around until the lead of the feeding chain joins the trailing mantas to form a large circle of feeding animals. As more and more animals join the circle, the column of mantas builds through the water to resemble an underwater cyclone of mantas which is approximately 15 metres in diameter. The spiralling mass of as many as 150 individual manta rays circle around together for as long as 60 minutes. The rotating cyclone always turns in an anticlockwise direction when viewed from above looking down onto the mantas. This collective teamwork is what inspired our supporters community called ‘The Cyclone’.
Sideways Feeding
Only recorded being undertaken by the manta ray species, the behavioural characteristics of sideways feeding are similar to straight feeding, except during the feeding runs the manta flips itself sideways, rotating the plane of its body 90 degrees away from the normal horizontal feeding position. The cephalic fins are also held out in a position perpendicular to the plain of the body, away from the manta’s head; very different to the standard cephalic fin position.
Bottom Feeding
Feeding individually, the manta or mobula swims along the seabed with its open mouth positioned within a centimetre of the bottom. The seabed forms a natural barrier to the ray's prey, so in manta rays the animal’s unfurled cephalic fins are usually splayed apart, positioned out away from the mouth to funnel any plankton in front of the approaching manta ray in towards the centre of the mouth. In mobula rays the cephalic fins are held in their more common central feeding position during bottom feeding.
Cleaning Behaviour
The world’s oceans can be an itchy place for its inhabitants to live, especially the larger ones, whose bodies present a much bigger target for waterborne parasites. On land, larger animals such as birds and mammals often cope with this problem by grooming and cleaning themselves and other members of their social group, using teeth, hands, beaks and claws to rid themselves of these irritating parasites. But fish like mobula and manta rays do not have hands or beaks, so they have found an animal group to do the job for them.
Lyretail Wrasse (Thalassoma lunare) and Bluestreak Cleaner Wrasse, (Labroides dimidiatus) cleaning a reef manta ray.
Clarion Angelfish (Holocanthus clarionensis) cleaning an oceanic manta ray in Mexico.
These animals are called cleaners, comprising mostly small reef fishes, although many shrimp species have evolved to become specialised cleaners as well. The cleaners set up shop at specific locations, usually a prominent reef outcrop or a coral bommie, and a whole host of client species make the trip each day to visit these ‘cleaning stations’.
This relationship between cleaner and client has long fascinated marine ecologists. It is widely showcased as the perfect example of mutually beneficial symbiosis, with both cleaner and client receiving an overall benefit from this cooperative behaviour.
Reef manta ray (Mobula alfredi) being cleaned by Blunt Headed Wrasse (Thalassoma amblycephalum) at a cleaning station.
These cleaning stations provide an ideal location to observe manta rays and are therefore often popular dive sites. However, unregulated tourism can have detrimental impacts on both the coral reef and the manta rays. To learn about sustainable tourism, please see our How to Swim With Mantas code of conduct toolkit.
Courtship, Mating & PreGNANCIES
Like all sharks and rays, but unlike the majority of other fish in the sea, mobulid rays reproduce through internal fertilisation; male and female must physically come together to mate. Manta and mobula rays give birth to live young that are small versions of their parents. Ready to fend for themselves, they are completely independent from birth.
Courtship
Courtship rituals and mating events are observed relatively infrequently, and the only documented accounts of a manta ray giving birth come from a single female housed in a public aquarium in Japan. No mobula ray have ever been recorded giving birth. Many gaps still remain in our knowledge of the life history strategies and reproductive behaviour of these animals, and what little we do know is based on limited scientific data, much of which comes from observations on just one species; the reef manta ray.
A male mobulid ray will often try his luck, testing the female’s receptiveness to his amorous advances by shadowing her movements. Positioning himself directly on top of her back. This behaviour soon attracts the attention of more amorous males, which follow in line behind the female to form a manta Conga dance – the ‘courtship train’ has begun!
As many as thirty males line up head-to-tail behind the female as she swims at great speeds, twisting and turning around the reef, even leaping from the water. When multiple receptive females are present, courtship trains can merge or divide. They are in a constant state of flux as new individuals join the queue and old males trail off the back. The trains run hot and cold, reaching periods of explosive speed and energy before slowing again into a graceful procession led by the female.
During the courtship train the female is not really trying to escape her pursuers. Instead, the train is a way for her to assess her suitors; she is testing the males before she makes her choice.
Copulation
A male reef manta ray (Mobula alfredi) biting onto the left pectoral fin of a female to mate.
Once the female is ready, she slows her swimming speed dramatically, often rising up into the water column as she waits for the male to make his move. The male bites down hard on the end of the female’s wing-tip, working as much as one metre (three feet) of her pectoral fin deep into his mouth. Once the male has a good grip on the female’s pectoral fin, he flips his body around and underneath hers so that they are positioned belly to belly. The male then inserts one of his two claspers into the female’s cloaca and ejaculates his sperm with thrusts of his abdominal region. Copulation itself lasts for just thirty seconds and the female remains motionless throughout, while the male continues to beat his pectoral fins, causing the mating couple to spiral around in slow motion in the water column.
When a male mobula or manta bites hold of the female’s pectoral fin during mating it causes minor cuts and abrasions to the upper and lower surface of the female’s wing-tip. The male’s teeth on the lower jaw often leave linear scrapes on the underside of the female’s fins, which are visible as red scratches. These marks quickly fade against the white colouration of the fin’s underside and are often hard to see just a few weeks after mating has occurred.
On manta rays, the male’s grip also causes scarring on the dorsal tips of the female’s pectoral fins, leaving behind white and/or black circular and oblong marks as the upper layers of skin are scraped away by sharp ridges on the supporting branchial arches in the roof of the male’s mouth. These dorsal mating scars are permanent and allow manta scientists to gauge what percentage of the female population consists of fully mature females. The fresh mating wounds on the underside of the pectoral fins also allow scientists to plot recent matings, which can be used to track pregnancies and reproductive trends over the following years.
Dorsal mating scars on the left pectoral fin of a sexually mature female reef manta ray (Mobula alfredi).
Ventral mating wounds on the left pectoral fin of a sexually mature female reef manta ray (Mobula alfredi).
Another interesting observation of these mating scars is their distribution. Over 95% of mating scars are present only on the female’s left pectoral fin. This trend for lateralisation is found in both species of manta rays around the world and is also observed in a wide variety of other species, including humans, most of whom favour the right-hand side of our bodies.
Pregnancies
A heavily pregnant reef manta ray (Mobula alfredi).
All mobulid rays reproduce via aplacental viviparity, meaning they give birth to live young that are hatched from an egg inside the female’s uterus. The pup, which is wrapped in a thin membranous egg case, hatches inside the mother’s oviduct and then feeds on the mother’s uterine milk until it is fully developed and ready to be born. No one has ever observed a manta or mobula ray giving birth naturally in the wild, however captive births of manta rays showed that the pups pop out of their mother’s cloacal opening with their pectoral fins rolled up over their back.
After a gestation period of just over a year, the female reef manta ray gives birth to a single pup (although occasionally they may also give birth to twins) which measures roughly 1.5 metres (5 feet) across from wing-tip to wing-tip at birth.
Under natural conditions, where food is limited and variable, female reef manta rays cannot usually sustain continual reproductive cycles of mating, pregnancies, and births without rest periods in between. The females therefore usually need seasonal gaps in their reproductive cycles to build up their energy reserves. On average, reef manta rays around the world give birth approximately once every 2 to 3 years and in some locations the reproductive rate is as low as one pup every 7 years.