Manta alfredi

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.

• Biogeographic Regions
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native
• australian australian
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native

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.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• reef reef
• coastal coastal

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.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

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.

• Development - Life Cycle
• indeterminate growth indeterminate growth

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.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• viviparous viviparous

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.

• 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.

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.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• solitary solitary

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.

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.

• Communication Channels
• visual visual
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical
• electric electric

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.

• Primary Diet
• planktivore planktivore

• Animal Foods
• aquatic crustaceans
• zooplankton zooplankton

• Foraging Behavior
• filter-feeding filter-feeding

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.

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.

Reef manta rays may have mutualistic relationships with remoras, as they clean the rays and feed on ectoparasite infestations.

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.

• Positive Impacts
• food food
• ecotourism ecotourism
• source of medicine or drug source of medicine or drug

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.

Additional Links

Encyclopedia of Life

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.

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., 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., 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., 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.