Reef manta rays are found primarily in the Indian and Pacific Oceans, including coastal waters surrounding Australia, Japan, South Africa, Thailand and Hawaii, as well as the Red Sea. Although they have been found in the Atlantic Ocean, such sightings are rare. (Fabrice, et al., 2012; Marshall, et al., 2012; Marshall, et al., 2009)
Reef manta rays are a marine species found in inshore habitats (within a few kilometers of land) in tropical and subtropical latitudes. They are often sighted near coral and rocky reefs in atolls and bays, likely due to the high densities of zooplankton associated with these areas. While it is known that they tend to avoid deep or open waters, the exact depth range in which they can be found is uncertain. (Anderson, et al., 2011; Marshall, et al., 2009; Marshall, et al., 2011)
Reef manta rays have wing-like pectoral fins and cephalic fin tips, or horns, that wrap around the mouth. Their central body disc is approximately two times longer than it is broad, with an average width of approximately 390 cm for adult females and 300 cm for adult males. The largest recorded specimen measured 550 cm in width. This is much smaller than giant manta rays (Manta birostris), a closely related species, which seldom measure smaller than 550 cm at maturity. Reef manta rays have a slender tail, with no distinct caudal spine. They are black in color dorsally and cream or white colored ventrally. A diagnostic feature of their coloration is the presence of light colored patches on the shoulder region, contrasting with the overall dark dorsal surface. Both the dorsal and ventral surfaces are covered in knob-like denticles, which are evenly distributed; ventral denticles are larger. They have a total of 918-1456 small, cusped teeth, which are each 1-2 mm in length. It is hypothesized that they have retained teeth for mating purposes, particularly as males have more pronounced teeth than females. Reef manta rays are sexually dimorphic. Females are larger than males and can be identified by a simple cloaca located between their ventral fins, as well as the presence of mating scars on the pectoral fins. Males possess two claspers, which extend from their pelvic fins. Juvenile males have claspers that do not extend past their pelvic fins and which are minimally calcified. The only external way to distinguish an adult female from a juvenile is by the presence of mating scars on the pectoral fins. (Kitchen-Wheeler, 2010; Marshall and Bennett, 2010; Marshall, et al., 2009)
The gestation period for reef manta rays is approximately a year, during which a fetus is nourished in the mother's uterus. They exhibit aplacental viviparity and definitive lipid histotrophic development; a fetus is nourished not by a placenta but with a protein and lipid-rich histotrophe, secreted by uterine villi. Typically, only one pup develops at a time. Newborn reef manta rays measure from 150 to 167 cm in disc width. It is very rare to find young individuals, and it has been hypothesized that juveniles may segregate themselves from the adult population until attaining adulthood, or that newborn/juvenile mortality is quite high. (Marshall and Bennett, 2010)
Females typically have a year-long resting period between pregnancies, with some individuals resting for up to 2 years. Because not all females participate in mating at a given time, females may display cues to show their receptiveness to males. There are five basic steps in reef manta ray mating: chasing, biting, copulation, post-copulation holding, and separating. Courting can take up to 2 hours, with males exhibiting their willingness to mate by swimming faster or in unison with other males, performing complex swim patterns, or breaching the water. If a female does not want to mate with a specific male she will buck and knock him off when he tries to copulate. Once a male has positioned himself with a female, he bites down on her pectoral fin and turns upside down. Scarring on females' pectoral fins suggests that lateralization occurs between the rays, with males favoring females' left pectoral fins. Copulation usually lasts 15 to 35 seconds, with the rays continuing to move through the water together. Once copulation is complete there is no further contact between mating pairs. (Marshall and Bennett, 2010)
Breeding season appears to be between October and January, followed by a gestation period estimated to last twelve months or more. Reef manta rays give birth to live young. Although capable of bearing young annually, females tend to reproduce biannually, likely due to energy constraints. It is most common for them to bear one pup, though it is possible to bear two. Maturity, estimated by size and the presence of mating scars, is reached at 400-490 cm disc width (8 years) for females and approximately 300 cm (6 years) for males. (Marshall and Bennett, 2010)
Although females nourish the pups before birth, there is no parental care given by either parent after birth; in fact, there are records of adults, possibly parents, attacking young shortly after birth. (Marshall and Bennett, 2010)
Re-sightings of individuals (identified by unique patterns of spots around their gill slits) have been recorded for spans of up to thirty years. It is estimated that this species may live at least forty years in the wild. While mortality rates are high in juveniles, adult mortality is low, probably due to their large size and a lack of predators. (Marshall, et al., 2012)
Although Reef manta rays are often found in groups when feeding, direct interactions between individuals seem to be limited to mating. The species displays site fidelity (preference for a particular area), likely associated with food availability, cleaning stations where parasites are removed by reef fishes, reproductive sites, and migratory landmarks. Manta rays are most commonly seen feeding during the afternoon. (Couturier, et al., 2011; Marshall and Bennett, 2010; Marshall, et al., 2012)
Daily migration distances can be up to 70 km, and annual migrations from 270-500 km. Home range size varies due to mating habits or productivity of different areas. Migrations appear to be linked to changes in temperature and zooplankton productivity. When monsoons occur, the shift in ocean currents affects which direction reef manta rays go, by allowing them to either move with the currents or encounter less difficulty navigating against them. The overall trend is that they migrate south in the summer and return north during the winter. It is also thought that the coral reefs and islands act as landmarks for the manta rays to orient themselves in their home range as well as help them navigate during migration. (Anderson, et al., 2011; Couturier, et al., 2011; Fabrice, et al., 2012; Marshall, et al., 2012)
The location of the eyes on the sides of the head allow reef manta rays to see in all directions; they communicate with each other through the courtship displays mentioned above. It also has been theorized that olfaction may play a role during courtship. They have well-developed electrosensory systems, as do all elasmobranchs, and are also able to detect sounds using their inner ears. (Marshall and Bennett, 2010; Montgomery and Bodznick, 1999; Perrine, 1999)
Reef manta rays are planktivores, feeding exclusively on zooplankton. When feeding, their cephalic horns are extended and their swimming becomes more deliberate. Plankton is filtered using the ventrally located gill slits. Reef manta rays follow the tidal changes that concentrate zooplankton in shallower atoll channels, increasing feeding rates. (Marshall and Bennett, 2010; Perrine, 1999)
Adult manta rays occasionally fall prey to orcas (Orcinus orca) and large sharks. The relatively large number of scars found on juveniles suggests that they endure more frequent attacks due to their smaller body size. (Marshall and Bennett, 2010; Marshall, et al., 2012)
Because reef manta rays have the capacity to consume large quantities of plankton, they may have a top-down effect on the structure of the marine communities that they inhabit. Further studies of this possible aspect of their ecology are needed. (Kitchen-Wheeler, 2010; Marshall, et al., 2012)
The presence of reef manta rays contributes to eco-tourism in areas such as Hawaii, East Africa, and Indonesia. In certain locations, tourists can be charged up to $3,000 to dive with mantas. In Asia however, this species is highly targeted by fisheries. Markets exist for their body parts, the cephalic horns in particular, which are sold for medicinal purposes or as delicacies. (Kitchen-Wheeler, 2010; Marshall, et al., 2012)
There are no known adverse effects of reef manta rays on humans.
The IUCN Red List has categorized reef manta rays as vulnerable, with the largest threat to these animals coming from commercial fishing. Whether accidental or intentional, fishing has caused an estimated 30% decrease in populations of reef manta rays globally. There is also concern that climate change could affect plankton abundance and thereby reef manta ray populations. The United States, Republic of Maldives, Philippines, and Western Australia have all established regulations or sanctuaries in an attempt to maintain healthy populations. (Marshall, et al., 2012; Marshall, et al., 2011)
Kourtney Simpkins (author), Indiana University-Purdue University Fort Wayne, Mark Jordan (editor), Indiana University-Purdue University Fort Wayne, Jeremy Wright (editor), University of Michigan-Ann Arbor.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
uses electric signals to communicate
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
A substance that provides both nutrients and energy to a living thing.
Animals with indeterminate growth continue to grow throughout their lives.
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
an animal that mainly eats plankton
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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