Download Social Lives - Manta Trust

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Social Lives
While mantas might seem like nomadic travellers,
voyaging the oceans in constant search of food rarely
interacting with other species, this is not the case. As
well as interacting with other members of their own
species during feeding events, at cleaning stations,
during courtship and of course when mating; mantas
also lend a helping hand to some other species,
playing host to a variety of hitchhiking parasites and
Blue-streaked and lunar tailed cleaner wrasse trail behind a large female reef manta
ray at a cleaning station in the Maldives, while two pale hitch hiking remora fish cling
upside-down to their ride with modified suction cup-like dorsal fins.
remoras. Furthermore, social interactions between
the manta rays themselves may be much more
complex than we currently believe......
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Ocean Oasis & Hitch Hikers
Manta rays are like floating islands, oasis sanctuaries for a whole host of
animals which seek the shelter, protection and sustenance these giants can
provide. Tiny parasites attach themselves to every surface of their bodies;
inside their pharynx and gills, around their mouths and in the mucus on the
manta's backs. Juvenile golden trevalleys (Gnathanodon speciosus) ride the
pressure waves in front of the giant’s head, like bow riding dolphins, these tiny
companions appear to lead the mantas, piloting them on their voyage across
the open seas. As soon as they are large enough to survive by themselves, the
golden trevalleys leave
the
shelter
giants
to
of
the
seek
protection together in
Three tiny juvenile golden trevalley's accompany a manta ray as it voyages
throughout the ocean; seeking shelter from predators close to the manta's
body if danger threatens.
shoals.
Another group of fishes have taken their association with, and dependency on, their larger hosts to
a whole new level. These fish are called remoras or suckerfish which, as their names suggest,
actually suck onto the bodies of their hosts using modified dorsal fins which act like a suction cup.
Short remoras accompany oceanic mantas wherever
they go, attaching themselves onto the manta at a
favoured spot which often results in red abrasions to
the mantas skin where the remora clings on.
This enables these fish to cling onto the bodies of the mantas, saving energy; they even venture
deep inside their host’s mouths to rest, find food or escape predation. One species, the White
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Suckerfish (Remorina albescens), actually spends its whole adult life inside the mouth
of manta rays, which must certainly be a little discomforting for the host. The benefits
to the remoras and suckerfish for living in such close association with their larger
hosts are clear, but there is debate about whether the manta rays receive a
significant return in benefits from these relationships. Certainly there are several
negative impacts; reduced swimming efficiency through extra drag created by having
to carry their hitch hikers, skin abrasions and sores created by the constant suction
attachments of the remoras, and the overall discomfort caused by having to put up
with as many as two dozen
of
these
fish
scurrying
around on, and inside, their
bodies.
This whale shark is adorned in a mass of hitch hiking short remoras
which cling to the underside of its body.
In most coastal reef manta ray populations there are several species of remoras which can be
found living on the bodies of the resident mantas. By far the most common is the Slender
Suckerfish (Echeneis naucrates); sometimes as many as a dozen of these 50cm long remoras can
swarm around a single manta, although 1-2 individuals per manta are most common. Another
Slender remoras, or shark suckerfish, are commonly
encountered attached to the underside of reef manta
rays throughout the tropics.
species often encountered is the Short Remora (Remora remora), although this large, compact and
brown remora is much more commonly seen on the oceanic mantas, appearing to prefer life in the
open ocean.
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Cleaning Giants
The world’s oceans can be an itchy place to live for its inhabitants, especially the larger ones, whose
bodies present a much bigger target for water bourn parasites to launch their attack upon. Tiny
ectoparasites live and feed on their host’s bodies, hiding themselves inside mouths, spiracles, gills
and anywhere else they can secure a firm grip out of harm’s way. And for filter feeding animals like
the manta rays, which spend much of their time swimming around with their mouths wide open,
particles of food and detritus
become lodged in their gills,
creating an unwanted buildup of dental detritus.
A clarion angelfish cleans ectoparasites off the tail of
an oceanic manta ray at Mexico's Revillagigedo
Islands.
On land larger animals, such as birds and mammals, often cope with this problem by
grooming and cleaning themselves; using teeth, hands, beaks and claws to rid
themselves of these irritating parasites. However, fishes like manta rays do not have
hands, or any other necessary tools with which to clean themselves, so instead, they
have found a group animals that can do the job for them. These animals are called
cleaners, and the vast majority are small reef fishes, although many shrimp species
Lunar wrasse swarm over the surface of this reef manta ray in search
of parasites to feed upon. The tiny cleaner fish venture deep inside
the mantas mouth and through its gills, which the manta opens wide
to allow better access for the wrasses.
have evolved to become specialised cleaners as well. The cleaners are small out of
necessity; their size enabling them to survive on, and pick off, the individual parasites
which cover their clients, even venturing right inside the bodies of their clients to
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reach those areas which would be inaccessible to a larger cleaner.
However, this size makes the cleaners less mobile, so instead of
travelling around in search of clients to clean, their clients come to
them.
The cleaners set-up shop at specific locations, usually a
prominent reef outcrop or 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 and is widely showcased as the perfect example of
mutually beneficial symbiosis, with both the cleaner and client
receiving an overall benefit from this cooperative behaviour. For the
cleaner the benefit comes from a ready supply of food which is
brought to them on a plate, which in this case is the body of their
clients. They remove irritating ectoparasites, algal growth, they clean
wounds by picking off dead skin and infectious bacteria and fungus,
and they also perform dentistry by swimming right inside the mouths
of their clients to remove food particles which have become lodged
Appearing to balance on its own tail, this manta strikes a head-stand posture, using
delicate beats of its flexible pectoral fins to hold it position inches above the seabed,
allowing the cleaner fish to do their job, while three slender remoras swim circles
around their unusually stationary and statuesque ride.
inside. For the clients the benefits appear to be obvious; having a local dentist, doctor and body salon all rolled into one package, with limited waiting times
and no reservations required.
Both species of manta rays visit cleaning stations and indeed manta ray cleaning stations are often the best locations in the world to dive or snorkel if you
want reliable encounters with these animals. In the Maldives for example there are hundreds of known manta ray cleaning stations, but some are much
more commonly used by the mantas than others. The most active sites are often those closest to the mantas favoured feeding sites, although this may
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fluctuate over time as seasonal abundances of food, or other environmental factors, cause the manta rays
to shift their preferences to other locations. It is likely that human disturbance, through sound pollution or
diver pressure is also responsible for abandonment of some cleaning stations by the resident manta ray
populations.
When a manta ray visits a cleaning station they glide within inches of the reef; slowing their forward
movement to the point at which they begin to stall and the rear end of their body begin to sink. If there is a
strong current the mantas are able to remain stationary above the cleaning stations, positioning themselves
A blue-streaked cleaner wrasse delicately
plucks parasites from the gills of a monocle
bream.
head first into the current to gain uplift, they hover with effortless ease. In slower currents the mantas move
in
slow
circles
above
the
station, lining up one behind
the other in a graceful slow motion dance, each manta taking its turn on top of
the cleaning station before peeling off to join the back of the queue. Upon
reaching the cleaning station the manta rays unfurl their cephalic fins and open
their mouths wide, inviting the cleaners to search every nook and cranny of
their body for the irritating parasites.
The most prevalent cleaner fish species are all members of the wrasse family; a
highly diverse and successful family of marine fish who owe their success to the
extendable tube-shape design of their mouths, which have evolved to allow
them to exploit a wide variety of food sources. Two of these wrasses, the Bluestreaked Cleaner Wrasse (Labroides dimidiatus) and the Bi-colour Cleaner
This juvenile manta ray has sustained a massive shark bite within days of
this image being taken. Amazingly though, even serious injuries like these
can be survived and heal well in time, especially with the assistance of the
cleaner fishes which help to keep the wound free from infection.
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Wrasse (Labroides bicolour) are specialized cleaners who spend their entire lives searching the bodies of a
multitude of coral reef fishes in search of ectoparasites. Another two fish species which regularly act as
manta ray cleaners are the Moon Wrasse (Thallasoma lunare) and the Two-tone Wrasse (Thallasoma
amblycephalum), both are gregarious by nature and often gather in huge numbers, rising up like a swarm of
bees to meet the approaching manta ray, which can provide the mother of all feasts for these tiny cleaners.
It’s not uncommon for a single manta to be covered with over a hundred of these industrious little cleaners
as they scour the manta for ectoparasites.
Manta rays are infested by a variety of parasite species, each adapted to inhabit specific areas of the mantas
body. Some ectoparasites live inside the thick mucus layer which coats the dorsal surface of the mantas
skin. These little lice are about the size of a grain of rice and can actually been seen scurrying around on the
backs of the mantas as they hover above the cleaning stations. Scientists inspecting the bodies of dead
manta rays have also discovered a host of other parasites which infest the gills and mouths of the manta
rays, so it is no surprise that the cleaner wrasses also concentrate their search for food in these areas as
well. The different cleaner species also divide the focus of their search; with the Two-tone Wrasses targeting
the mantas backs and bellies, while the other three species prefer to enter right into the mantas mouths
A chain of manta rays work cooperatively
while feeding to maximise the amount of
plankton they can engulf.
and gill openings in search of trapped food and internal parasites.
Sometimes the tranquillity of the cleaning is broken when a cleaner bites a particularly sensitive part of a
mantas body, sending it flying away from the cleaning station as great speed, trailing a stream of fleeing cleaners which pour from the mantas body as it
goes. Occasionally these accelerations are directed upwards towards the water’s surface, as the manta leaps clear out of the water before gravity bring its
immense bulk crashing back into the sea.
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Social Societies
Manta rays in the Maldives regularly spend many hours each day visiting favoured cleaning stations, cruising along the reef or hovering above the cleaning
station to allow the cleaners access to their bodies. These sites are obviously extremely important to the population as a whole; serving as focal points for
mating activity as well as the obvious function of cleaning. However, these explanations, while they are undoubtedly important contributing factors, they
do not fully explain the reasons why some sections of the population spend so much more time at cleaning stations than others. While male and juvenile
manta rays both regularly visit cleaning stations, the frequency of their
visits, and the length of time they spend cleaning, are significantly less
than the large females in the population.
Over five years researchers have identified over 400 individual manta rays
visiting one particular cleaning station in the Maldives, amassing
thousands of visitation records for the population as a whole which is
split roughly evenly between males and females. However, during the
study period a core group of 60 large females accounted for over 50% of
all recorded sightings, indeed of this site's top 100 visiting manta rays, 73
are large females. If the motivation for manta rays to visit cleaning
stations was simply a mechanism for having parasites removed from their
bodies, we would not expect to see such variations in visitations within
the population, as parasite loads are unlikely to vary significantly enough
between the sexes to warrant such polarized trends.
Four fully grown mature female reef manta rays hover effortlessly above a
cleaning station in the Maldives. These four females are part of a core group of
mantas which often frequents this site (and others) at the same times throughout
the year.
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So why do the females spend so much more time at these cleaning sites than the males? The simple answer is that we just don’t know, however a likely
possibility is that male manta rays spend more time roaming from location to location in search of mates, while the females remain faithful to a specific
home range, only venturing further afield if the drive for food dictates. In the Maldives female manta rays show very strong site fidelity, returning to the
same feeding and cleaning stations on a regular basis throughout their adult lives, which span many decades. Each area appears to have its own core
population of individuals which have learned how best to maximise their planktonic food requirements from their home range, which often occurs in very
patchy bursts of abundance with the regular ebb and flow of the tides. As a result, it appears these individuals have plenty of time on their hands (or rather
fins) to play with, and many of them make a bee line for their favourite cleaning station during these periods of lull in feeding activity. Once at the cleaning
station, the females may engage in mating activity at specific times of the year, get cleaned, or simply enjoy the sensation of being groomed by the cleaner
fishes. The first few hours after sunrise are the peak periods for cleaning activity, which is not surprising as cleaner fish are active only by day, so each
morning the mantas are itching to be cleaned.
It is also possible that these core groups of females are linked by more than simply habitat utilization, with social associations and possibly genetic
relatedness binding the group together, as younger females learn the habits of the older and more knowledgeable individuals. The extent to which these
clearly defined groupings at specific cleaning stations link these females together on a larger scale, both geographically and temporally, is only just
beginning to be pieced together. And to what degree social interactions, or merely functions of habitat utilization, are the ultimate driving forces behind
these associations still remains to be seen.
Want to know more? (Visit our website: www.mantatrust.org)