Animal Diversity Web

Diversity

Scarids, which are widely known as parrotfishes because of their beak-like jaws, include approximately nine genera and 83 species. They are abundant in tropical reefs around the world and well known to divers for their striking coloration and noisy feeding as they crunch on dead coral. Parrotfishes exhibit several types of complex mating systems that vary more by geographic location than by species (see Reproduction). They also have considerable ecological impacts on coral reefs through herbivory and bioerosion (see Ecosystem Roles). (Choat and Bellwood, 1998; Nelson, 1994; Thresher, 1984)

Geographic Range

Parrotfishes are found primarily in tropical waters throughout the Atlantic, Indian, and Pacific oceans. However, some species inhabit subtropical waters, and some, such as Scarus ghobban, may venture far from reef environments. (Choat and Bellwood, 1998; Nelson, 1994)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native
• indian ocean
  • native
• atlantic ocean
  • native
• pacific ocean
  • native
• mediterranean sea
  • native

Habitat

Most parrotfishes exclusively inhabit offshore coral reefs in tropical regions. However, a few species feed primarily on sea grasses and are most common in the Caribbean. Two other species, Nicholsina denticulate and Sparisoma cretense, are common over rocky reefs of the Gulf of California and Mediterranean Sea, respectively. (Choat and Bellwood, 1998; Nelson, 1994)

• Habitat Regions
• saltwater or marine

• Aquatic Biomes
• pelagic
• reef
• coastal

Systematic and Taxonomic History

Scarids are one of several recently derived families (Acanthuridae, Monacanthidae, Pomacentridae, Blenniidae, Siganidae) capable of exploiting reef algae and small colonial invertebrates. Reef herbivory was primarily restricted to post-Cretaceous perciformes until these families underwent rapid evolution during the early Tertiary, 50 to 30 million years ago. The modified pharyngeal apparatus , which parrotfishes use to grind dead corals into a digestible paste, is an important adaptation that has allowed parrotfishes to exploit reef algae and small colonial invertebrates (see Physical Description and Food Habits for further information). Brucae and Randall (1983 and 1985) (in Nelson 1994) created two subfamilies of parrotfishes: Scarinae with four genera containing approximately 67 species, and Sparisomatinae with five genera and 16 species. Randall (1983 and 1985) (in Nelson 1994) created two subfamilies of parrotfishes: Scarinae with four genera containing approximately 67 species, and Sparisomatinae with five genera and 16 species. (Choat and Bellwood, 1998; Harmelin-Vivien, 2002; Nelson, 1994)

Physical Description

Parrotfishes are characterized by their distinctive beak-like jaws, in which the teeth are fused together in most species, and a pharyngeal apparatus , which acts as a second set of jaws in the throat. In the pharyngeal apparatus, the teeth are arranged in rows and are highly specialized to grind, crop, and crush food as it is processed. Parrotfishes have large, cycloid scales , usually with 22-24 scales along the lateral line. The dorsal fin has nine spines and ten soft rays. The anal fin has three spines and nine soft rays, and the pelvic fins one spine and five soft rays. (Click here to see a fish diagram). (Choat and Bellwood, 1998; Nelson, 1994)

Some parrotfishes have a complex socio-sexual (socially influenced sexual change) system punctuated by three phases, and each phase change results in a different color pattern (See Reproduction: Mating Systems for a description of “phases” in parrotfishes). For instance, juveniles tend to have a drab mixture of browns, grays and blacks, but as they mature a distinct coloration emerges with the addition of red tones. A third set of colors is donned by males and by females that have recently undergone sex change into males. As these males mature, they exhibit bright, intricate patterns of reds, greens, and blues. This type of color change has been documented in Scarus, Sparisoma, Nicholsina, Bolbometapon, and Cryptotomus, but there are some monochromic (fishes that do not exhibit sexual color change) species that exhibit different types of sexual dimorphism. (Choat and Bellwood, 1998; Thresher, 1984)

Scarus coelestinus and Scarus coeruleus in the eastern Pacific and Scarus niger in the Indo-West Pacific exhibit no color differences. However, mature males of Scarus coelestinus and Scarus coeruleus develop more squared-off and prominent foreheads than smaller fish, while Scarus niger exhibits no physical differences other than size. Finally, fleshy tips on the upper and lower lobes of the caudal fin can be observed in mature males of Scarus rubroviolaceus, but are poorly developed on small males and females. (Thresher, 1984; Wheeler, 1985)

• Other Physical Features
• ectothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful
• sexes shaped differently
• ornamentation

Development

Tidal currents disperse parrotfish eggs, which begin to hatch approximately 25 hours after fertilization. Newly hatched larvae begin to feed after three days but the length of the planktonic stage is unknown. Most parrotfish species develop rapidly and reach maturity between two and four years. (Choat and Bellwood, 1998; Thresher, 1984)

Reproduction

Parrotfishes utilize some of the most complex and unusual reproduction systems known to fishes. Males can be either primary, i.e. born male, or secondary, i.e. females that have undergone sex change. In some species there are no secondary males while in others all individuals are born female (monandric) and change sex when necessary. In the most complex systems, species are diandric – both primary and secondary males exist in the population. In these species, individuals proceed through three distinct phases, marked by color differences. In fact, the color differences are so pronounced that for over 200 years researchers regarded some phases as distinct species. Sexually immature and drab colored juveniles represent the first phase. The second, known as the initial, phase (IP) can include sexually mature males or females, which are impossible to tell apart without internal examination or observation during spawning. The terminal phase (TP) includes only mature males, which display brilliant colors. TP males usually dominate reproductive activity through a harem-based social system. The death of a TP male serves as a social cue for an IP female to change sex and behavior. The morphology and behavior of IP males may also change in response to the death of a TP male. In some cases IP males attempt to infiltrate a TP male’s harem by masquerading as a female. In the so called “sneak spawning” attempt IP males follow spawning pairs into the water column and release a large cloud of gametes at peak spawning in an attempt to overwhelm fertilization by the TP male. IP males are well equipped to perform “sneak spawning” as they have larger testes and so are able to produce more gametes, while TP males have smaller testes and rely on aggression to deter other males. (Choat and Bellwood, 1998; Thresher, 1984)

The type of reproductive behavior described above and whether it involves paired, foraging group or mass spawning depends on a complex set of behavioral and geographic factors. For instance, some species, such as Scarus iseri, exhibit a wide range of reproductive behaviors depending on the area in which they are found. In Panama, Scarus iseri employs a system involving three classes of individuals: territorials, stationeries and foragers. Territorials are organized into groups that consist of a dominant female, several subordinate females and usually, but not always, a terminal (TP) male. Paired spawning occurs within the territory, which both males and females defend. Stationaries consistently use the same area for spawning but do not defend it, and foragers include groups of up to 500 individuals, mostly females. In Puerto Rico, initial phase (IP) and terminal phase (TP) individuals migrate to temporary spawning areas in deep water, usually in pairs. Finally, in Jamaica Scarus iseri emphasizes aspects of the foraging group system and spawning only takes place in groups. The three previous examples illustrate the flexibility of the socio-sexual mating systems found in parrotfishes. The reasons that different aspects of the basic spawning system manifest in different areas range from population density to competition for spawning sites and other resources to geographic factors like seasons and water temperature. (Thresher, 1984)

• Mating System
• polygynous
• polygynandrous (promiscuous)

In general, parrotfishes spawn year-round, usually at dusk. However, peak spawning occurs in summer for many species and there is evidence that some species have defined non-spawning periods. As discussed above, many species migrate to the outer edges of the reef to spawn but some spawn within defined territories. There is evidence that some scarids respond to the lunar cycle during spawning, but in others, spawning correlates closely with high tide, regardless of the time of the lunar month. In species that spawn several times during the day, the tidal cycle is followed closely since this is the optimal time for egg dispersal. (Choat and Bellwood, 1998; Thresher, 1984)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• year-round breeding
• sequential hermaphrodite
  • protogynous
• sexual
• fertilization
  • external
• oviparous

There is no evidence of parental behavior in parrotfishes. (Thresher, 1984)

• Parental Investment
• no parental involvement

Lifespan/Longevity

The maximum age of most parrotfishes is less than 20 years and most live less than five years. There is a general trend in the scarids for larger species to live longer. Subsequently, the largest scarid, Bolbometopon muricatum, is the one exception to the 20 year maximum age. (Choat and Bellwood, 1998; Choat and Robertson, 2002)

Behavior

Parrotfishes are most well known for their complex social structures. Most are organized into male-dominated harems but others breed cooperatively or in pairs (see Reproduction: Mating Systems & General Behavior for more on social systems). Some parrotfishes are highly territorial while others are mainly nomadic, with the home range increasing as the size of the fish increases. Large foraging groups of up to 500 individuals form for spawning and to deter predators while feeding. Parrotfishes feed continuously throughout the day and seek shelter in reefs at night. (Böhlke and Chaplin, 1994; Thresher, 1984)

• Key Behaviors
• natatorial
• diurnal
• motile
• territorial
• social
• colonial
• dominance hierarchies

Communication and Perception

Most known forms of communication in parrotfishes are related to reproduction and are discussed in Reproduction: Mating Systems. However, in some species male coloration intensifies when defending its territory, which suggests that visual cues are used to deter invaders. (Thresher, 1984)

• Communication Channels
• visual
• tactile

• Perception Channels
• visual
• tactile
• chemical

Food Habits

Parrotfishes are primarily herbivorous, grazing intensively on dead, algae-coated coral, vegetable material, and in some species sea grasses. Bump-headed parrotfishes, which consume significant amounts of live coral, are one exception. Key to the success of parrotfishes is their ability to take up plant material, detritus and calcareous sediment and process it through the action of the pharyngeal jaw. This chewing mechanism grinds ingested material into a fine paste and breaks down algal cells, releasing the cellular material for digestion. Like acanthurids, parrotfishes form large feeding groups, sometimes with multiple species, to overwhelm territorial fishes and deter predators. (Choat and Bellwood, 1998; Thresher, 1984)

• Primary Diet
• herbivore

Predation

A unique feature of some parrotfishes is the production of a mucous envelope at night before resting. The envelope takes about 30 minutes to construct and is open at both ends to allow water flow. The secreted envelope is foul smelling and tasting, which may serve to deter nighttime predators that hunt by scent. Most parrotfishes seek out caves and ledges in the reef for protection at night, but parrotfishes in the genus Cryptotomus bury themselves in the sand like wrasses. After creating a hole in the sand Cryptotomus then produces its mucous nightgown. (Böhlke and Chaplin, 1994; Choat and Bellwood, 1998; Nelson, 1994)

• Known Predators

  • sharks (Chondrichthyes)
  • humans (Homo sapiens)

Ecosystem Roles

Parrotfishes have a major impact on coral reefs through intensive grazing and associated bioerosion. The grazing patterns of large schools of parrotfish have the effect of selecting for certain species of corals and algae, and preventing algae from choking out corals. Many parrotfishes feed on calcareous algae (algae that are high in mineral calcium) growing on dead, exposed coral by biting off chunks and turning them into a fine paste. This type of grazing contributes significantly to the process of bioerosion and the creation of sediment on reefs. For instance, it has been calculated that a single large parrotfish, Bolbometapon muricatum (bump-head parrotfish), consumes approximately one cubic meter of coral skeletons per year, and turns it into fine sediment. In this way large schools of bump-head parrotfish determine the fine-scale topography of coral reefs. (Choat and Bellwood, 1998)

A separate ecological consequence of intense herbivory in parrotfishes is the conversion of plant material into fish flesh. The success of parrotfishes in consuming plant material unavailable to most other fishes and the large size of parrotfish populations makes them an important part of the predatory food chain. (Choat and Bellwood, 1998)

• Ecosystem Impact
• biodegradation

Economic Importance for Humans: Positive

In the Bahamas, the scales of some parrotfishes are used for decorating basketwork and shellflower arrangements, but the fish are not consumed. In other areas, parrotfishes are sometimes taken as food, but their flesh can be dangerous to humans as a result of accumulated ciguatera toxins. (Böhlke and Chaplin, 1994)

• Positive Impacts
• food
• body parts are source of valuable material
• research and education

Economic Importance for Humans: Negative

Several species, such as blue parrotfish and one Indo-Pacific species, have caused ciguatera (fish poisoning sickness) in humans, which can be fatal. (Böhlke and Chaplin, 1994)

• Negative Impacts
• injures humans

Conservation Status

One scarid, Scarus guacamaia (rainbow parrotfish), is listed as vulnerable to extinction. (The World Conservation Union, 2002)

• IUCN Red List [Link]

  Not Evaluated

Other Comments

The fossil history of scarids dates back to the lower Tertiary and Eocene epochs. (Berg, 1958)

Contributors

R. Jamil Jonna (author), Animal Diversity Web.

References

Berg, L. 1958. System Der Rezenten und Fossilen Fischartigen und Fische. Berlin: VEB Deutscher Verlag der Wissenschaften.

Böhlke, J., C. Chaplin. 1994. Fishes of the Bahamas and Adjacent Tropical Waters. Wynnewood, Pa: Published for the Academy of Natural Sciences of Philadelphia by Livingston.

Choat, H., D. Bellwood. 1998. Wrasses & Parrotfishes. Pp. 209-210 in W Eschmeyer, J Paxton, eds. Encyclopedia of Fishes – second edition. San Diego, CA: Academic Press.

Choat, J., D. Robertson. 2002. Age-Based Studies. Pp. 63-67 in P Sale, ed. Coral Reef Fishes: Dynamics and Diversity in a Complex Ecosystem. San Diego, CA: Academic Press.

Harmelin-Vivien, M. 2002. Energetics and Fish Diversity on Coral Reefs. Pp. 268-269 in P Sale, ed. Coral Reef Fishes: Dynamics and Diversity in a Complex Ecosystem. San Diego, CA: Academic Press.

Nelson, J. 1994. Fishes of the World – third edition. New York, NY: John Wiley and Sons.

The World Conservation Union, 2002. "IUCN 2002" (On-line). IUCN Red List of Threatened Species. Accessed August 02, 2003 at http://www.iucnredlist.org/.

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

Wheeler, A. 1985. The World Encyclopedia of Fishes - second edition. London: Macdonald.