Acanthurus coeruleus

Geographic Range

Blue tangs, Acanthurus coeruleus , live on shallow marine reefs throughout the western Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea. Blue tangs range from New York in the north to the Amazon delta in Brazil. They are found east to Bermuda and Ascension Island but are most common in the Caribbean, and coastal Florida and the Bahamas.

• Biogeographic Regions
• atlantic ocean atlantic ocean
  • native native

Habitat

Blue tangs live primarily on hard-coral reefs. They can also be found near soft corals, rubble, seagrass beds, and algal beds. Young fish prefer areas with plenty of cover. Breeding individuals congregate at flat, sandy areas between patches of reef. They shelter in coral holes and crevices. Blue tangs can be found at depths of 2 to 40 meters.

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

• Aquatic Biomes
• reef reef
• coastal coastal

Physical Description

Acanthurus coeruleus reaches 39 cm in length. A sexually mature fish is typically over 10 cm in length. Adult coloration is deep blue and occasionally purple. Mature fish are able to temporarily change color between near-black and pale white. These color shifts can encompass the entire fish or portions of it and are different between the sexes. Similar to other fishes in the family Acanthuridae , Acanthurus coeruleus is a laterally compressed, pancake-shaped fish with high eyes, a subterminal mouth, yellow caudal spine at the base of the tail, and a dorsal fin that ends at the caudal peduncle. Juveniles are bright yellow. Older juveniles are blue or orange-brown with grey stripes. The sharp caudal spine is found in a horizontal groove on the peduncle and can be extended during aggressive interactions. Acanthurus coeruleus has 9 dorsal spines, 26-28 dorsal soft rays, 3 anal spines, and 24-26 anal soft rays.

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

• Sexual Dimorphism
• sexes alike

Development

Eggs take 24 hours to hatch. Upon hatching, the pelagic larvae are less than 2 mm in length. The young, called ""acronuri"", are transparent, silvery, and diamond-shaped. They begin to develop scales and dorsal and anal fins at 2 to 6 mm in length. The caudal spine appears when the larvae reach 13 mm in length. Older acronuri drift to nearshore areas where they meta morphose into juveniles, including losing their silver color, developing a more rounded profile, and developing an elongated snout.

• Development - Life Cycle
• metamorphosis metamorphosis
• indeterminate growth indeterminate growth

Reproduction

Blue tangs generally mate in large resident aggregations over sandy patches between reefs. These fish seem to prefer locations 6 to 10 m deep with reasonably strong currents to sweep the fertilized eggs to sea. Mating readiness is indicated by color changes in the adults, who change from a uniform deep blue to pale blue on the front half of the body and dark blue on the rear half of the body. Courting females and a small number of males break off from the aggregation and release gametes at the water's surface in a behavior called a "spawning rush." Often, spawning rushes are not successful and are broken off by the female. Pair spawning is limited to small populations.

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

Prior to a spawning aggregation, small groups of fish travel from nearby reefs before forming schools of over one-hundred individuals. Although spawning aggregations typically occur every day at a given location, they are often restricted to less than 20 individuals. The largest spawning occurs in the late afternoon three to eight days following the full moon in the winter months. However, the exact variables contributing to spawning aggregations are still unknown. It is likely that offshore currents, moon phase, predator abundance, and light levels all play a role in predicting spawning aggregations. Generally, spawning aggregation sites are also used by Acanthurus bahianus and members of the genera Scarus and Sparisoma . Sexual maturity is reached after one year.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sequential hermaphrodite
  • protandrous protandrous
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Parental care is absent in this species.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female

Lifespan/Longevity

Blue tangs live up to 12 to 15 years in the wild.

Behavior

Juvenile blue tangs are solitary and occupy home ranges that increase with body size. Juveniles aggressively defend their home ranges from A. bahianus juveniles. Juveniles also avoid damselfishes ( Stegastes ), that overlap in range with them. Adult blue tangs have three social modes: territorial, wandering, and schooling. Territorial adults chase conspecifics. Schooling adults are not aggressive. Wanderer adults are not aggressive nor do they interact with other individuals like schooling fish do. Wanderers are mostly chased by other fish including conspecifics, ocean surgeons ( A. bahianus ), and damselfish ( Stegastes ) (Morgan and Kramer, 2004). Occasionally large, multi-species aggregations are formed, including doctorfish ( A. chirurgus ) and other surgeonfish ( Acanthurus ).

Blue tangs are active during the day, hiding in crevices on the reef at night to avoid predators. They are not migratory. Juveniles are rarely seen on reefs, because of their dependence on cover, but intermediate phases and adults are common.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial
• social social

Home Range

Home ranges increase relative to body size.

Communication and Perception

Blue tangs use vision to communicate and to locate food. They may also use chemical cues and touch, but little is known about communication and perception channels in these fish.

• Communication Channels
• visual visual
• tactile tactile

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Blue tangs are herbivorous as adults, feeding largely on filamentous algae. They avoid eating calcareous material, like corals, because they lack the gizzard-like stomach of other surgeonfishes . Acanthurus coeruleus individuals feed singly, in small groups, or in large aggregations numbering over 100. Large aggregations can and in these groups can ravish damselfish gardens on reefs. Blue tangs that live in smaller populations do more foraging in the water column. Blue tangs will also eat plankton.

• Primary Diet
• herbivore herbivore
  • algivore

• Animal Foods
• zooplankton zooplankton

• Plant Foods
• algae
• phytoplankton phytoplankton

Predation

Predators include reef sharks , tunas , snappers , jacks , groupers , and barracudas . Juveniles may also be taken by trumpetfish . Pelagic eggs are commonly eaten by small bar jacks , yellowtail snappers , and the black durgon .

Because of their flattened shape and sharp caudal spines, it is difficult for predators to swallow blue tangs.

Defense from predators while grazing and spawning is also accomplished by schooling. Attacks are more often observed on solitary fish.

Ecosystem Roles

Blue tangs help keep algae populations under control, which prevents the overgrowth and suffocation of corals. Increases in algal density have greatly increased blue tang population size. Most blue tangs move within single reef habitats but they may also live on wider ranges around the reef.

Juveniles graze algae and pick molted skin and parasites from green turtles ( Chelonia mydas ) in cleaning stations with surgeonfish ( Acanthurus chirurgus ) and sergeant majors ( Abudefduf saxatilis ).

Economic Importance for Humans: Positive

Blue tangs are sometimes used as a bait fish. They are important in the aquarium trade, where they are popular fish. Blue tangs, and other reef fish, attract ecotourism in the form of snorkeling and diving.

• Positive Impacts
• pet trade pet trade
• ecotourism ecotourism

Economic Importance for Humans: Negative

Blue tangs can cause ciguaterra poisoning if eaten. Their sharp caudal spine can cause painful injuries if people try to handle them. Their sudden movements can cause the spine to create a deep wound, posing a risk of infection. Some species of Acanthurus may have venom associated with the spine as well.

• Negative Impacts
• injures humans
  • bites or stings

Conservation Status

Acanthurus coeruleus is a secure species. It is not on the IUCN Red list.

Other Comments

The genus name Acanthurus means “thorn tail”, which refers to the spine on the caudal peduncle.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Genna Woodruff (author), Hood College, Lori Wollerman (editor, instructor), Hood College.

References

Bell, T., D. Kramer. 2000. Territoriality and Habitat Use By Juvenile Blue Tangs, Acanthurus coeruleus . Environmental Biology of Fishes , 58: 401-409.

Bester, K. 2005. "Ichthyology at the Florida Museum of Natural History" (On-line). Accessed September 13, 2005 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/BlueTang/BlueTang.html .

Deloach, N. 1999. Reef Fish Behavior:Florida Caribbean Bahamas . Jacksonville: New Worold Publications.

Froese, R., D. Pauly, D. Woodland. 2003. "Fish Base" (On-line). Accessed September 12, 2005 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=944 .

MarineBio.com, 2005. "Acanthurus coeruleus" (On-line). Marine Biology. Accessed September 12, 2005 at http://www.marinebio.com/species.asp?id=277 .

Morgan, I., D. Kramer. 2004. The Social Organization of Adult Blue Tangs, Acanthurus coeruleus, on a fringing reef, Barbados, West Indies.. Environmental Biology of Fishes , 71: 261-273.

Thresher, R. 1984. Reproduction in Reef Fishes . Neptune City, NJ: T.F.H. Publications.