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Manta alfrediAlfred manta(Also: Inshore manta ray; Manta ray; Prince Alfred's ray)

By Kourtney Simpkins

Geographic Range

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)

Habitat

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)

Physical Description

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)

  • Sexual Dimorphism
  • female larger
  • Range length
    150 to 550 cm
    59.06 to 216.54 in

Development

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)

Reproduction

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)

  • Breeding interval
    Females mate once every 1-2 years.
  • Breeding season
    Breeding season is typically October through January.
  • Range number of offspring
    0 to 2
  • Range gestation period
    4 to 13 months
  • Average gestation period
    12 months
  • Average age at sexual or reproductive maturity (female)
    8 years
  • Average age at sexual or reproductive maturity (male)
    6 years

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)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • provisioning
      • female

Lifespan/Longevity

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)

  • Range lifespan
    Status: wild
    30 (high) years
  • Average lifespan
    Status: wild
    25 years
  • Typical lifespan
    Status: wild
    40 (high) years
  • Average lifespan
    Status: wild
    30 years

Behavior

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)

Home Range

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)

Communication and Perception

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)

Food Habits

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)

Predation

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)

Ecosystem Roles

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)

Reef manta rays may have mutualistic relationships with remoras, as they clean the rays and feed on ectoparasite infestations. (Marshall, et al., 2012; Tang, et al., 2013)

Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

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)

Economic Importance for Humans: Negative

There are no known adverse effects of reef manta rays on humans.

Conservation Status

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)

Contributors

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.

Glossary

Atlantic Ocean

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.

World Map

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Pacific Ocean

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.

World Map

acoustic

uses sound to communicate

bilateral symmetry

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.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

ecotourism

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.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

electric

uses electric signals to communicate

fertilization

union of egg and spermatozoan

filter-feeding

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.

food

A substance that provides both nutrients and energy to a living thing.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

iteroparous

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).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

reef

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.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Anderson, R., M. Adam, J. Goes. 2011. From monsoons to mantas: seasonal distribution of Manta alfredi in the Maldives. Fisheries Oceanography, 20/2: 104-113. Accessed June 12, 2013 at http://www.iotc.org/files/proceedings/2011/wpeb/IOTC-2011-WPEB07-INF17.pdf.

Couturier, L., F. Jaine, K. Townsend, S. Weeks, A. Richardson, M. Bennett. 2011. Distribution, site affinity and regional movements of the manta ray, Manta alfredi (Kreft, 1868), along the east coast of Australia. Marine and Freshwater Research, 62/6: 628-637. Accessed June 12, 2013 at http://www.publish.csiro.au/?act=view_file&file_id=MF10148.pdf.

Fabrice, J., L. Couturier, S. Weeks, K. Townsend, M. Bennett, K. Fiora, A. Richardson. 2012. When giants turn up: sighting trends, environmental influences and habitat use of the manta ray Manta alfredi at a coral reef. PLoS ONE, 7/10: e46170. Accessed March 01, 2013 at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046170.

Kitchen-Wheeler, A. 2010. Visual identification of individual manta ray (Manta alfredi) in the Maldives Islands, Western Indian Ocean. Marine Biology Research, 6/4: 351-363. Accessed March 01, 2013 at http://www.tandfonline.com.proxy.lib.umich.edu/doi/full/10.1080/17451000903233763#.Ubidqq6veRk.

Marshall, A., M. Bennett. 2010. Reproductive ecology of the reef manta ray Manta alfredi in southern Mozambique. Journal of Fish Biology, 77/1: 169-190. Accessed March 01, 2013 at http://onlinelibrary.wiley.com.proxy.lib.umich.edu/doi/10.1111/j.1095-8649.2010.02669.x/full.

Marshall, A., L. Compagno, M. Bennett. 2011. "Manta alfredi, Alfred manta" (On-line). Fish Base. Accessed March 01, 2013 at http://fishbase.us/summary/Manta-alfredi.html.

Marshall, A., T. Kashiwagi, M. Bennett, M. Deakos, G. Stevens, F. McGregor, T. Clark, H. Ishihara, K. Sato. 2012. "IUCN Red List of Threatened Species Manta alfredi" (On-line). IUCN Red List. Accessed March 01, 2013 at http://www.iucnredlist.org/details/195459/0.

Marshall, A., L. Compagno, M. Bennett. 2009. Redescription of genus Manta with resurrection of Manta alfredi (Krefft, 1868) (Chondrichthyes; Myliobatoidei; Mobulidae). Zootaxa, 2301: 1-28. Accessed March 06, 2013 at http://www.mapress.com.proxy.lib.umich.edu/zootaxa/2009/2/zt02301p028.pdf.

Montgomery, J., D. Bodznick. 1999. Signals and noise in the elasmobranch electrosensory system. The Journal of Experimental Biology, 202: 1349-1355. Accessed June 13, 2013 at http://jeb.biologists.org/content/202/10/1349.full.pdf.

Perrine, D. 1999. Sharks and Rays of the world. Stillwater, MN: Voyageur Press, Inc..

Tang, D., B. Venmathi Maran, Y. Matsumoto, K. Nagasawa. 2013. Redescription of Lepeophtheirus acutus Heegaard, 1943 (Copepoda: Caligidae) parasitic on two elasmobranch hosts off Okinawa-jima Island, Japan. Journal of Natural History, 47/5-12: 581-596.

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