Scarus is a genus of parrotfishes. With 52 currently recognised extant species,[3] it is by far the largest parrotfish genus. The vast majority are found at reefs in the Indo-Pacific, but a small number of species are found in the warmer parts of the eastern Pacific and the western Atlantic, with a single species, Scarus hoefleri in the eastern Atlantic.[3]
The genus name Scarus comes from the Greek word σκάρος (skáros), which refers to parrotfishes.[4]
Evolution
Scarus is most closely related to its sister genusChlorurus. Most recent phylogenetic analyses find that the two genera diverged during the late Miocene (Messinian).[1] In both genera, most of their diversification occurred some time later, within the last 3.5 million years during the Pliocene.[5] In contrast, coral reefs in their modern form were established much earlier, during the Miocene.[1]
Most Scarus species occur in reef habitats. However, some of the more basal species such as S. zufar occur in rockier, more peripheral habitats, suggesting that this may be the ancestral habitat type for the genus.[1]
A 2012 phylogenetic analysis of 45 Scarus species recovered 10 major monophyletic clades.[1]
Description
Adults of most species reach maximum lengths of between 30 and 50cm (12–20in), but the rainbow parrotfish (Scarus guacamaia) can grow to lengths of 1.2m (3.9ft)[3] and is the second largest species of parrotfish after the humphead parrotfish[6]. S. guacamaia weighs a hundred times more than the smallest Scarus species Scarus iseri,[1] which only reaches a maximum length of 27 cm.[7]
In comparison to its sister genus Chlorurus, Scarus species in general have less obtuse head profiles, less extensive cheek areas, and smaller dental plates, although a few relatively basal species of Scarus are exceptions to this. This may possibly reflect comparatively lower biting power, and a disparity in the ability to excavate calcareous reef subtrata.[1]
Sexual dichromatism
Most Scarus species are very colourful, and most are sexually dichromatic, with strikingly different initial (male and female) and terminal (male only) phases.[3][8] However in a few species, initial phase and terminal phase colouration remains the same. Examples of such sexually monochromatic species include S. guacamaia, S. coelestinus, S. perrico, S. niger,[8], and S. coeruleus.[6]
Ecology
S. coelestinus with S. guacamaia in Florida, two extremely closely related species. Unlike most Scarus species, these two are not sexually dimorphic. Due to their similar appearance and sympatry, they were often thought to be colour phases of the same species until the 1960s.
Scarus species are important herbivores in reef ecosystems, feeding predominantly on algae and dead coral.[10] In the process, they facilitate bioerosion and create sediment.[11]
Lifespan varies across different species. More short-lived species, such as the common parrotfish (S. psittacus), live for up to 6 years.[7] Other species are more long-lived; the endangered greenback parrotfish (S. trispinosus) has been recorded living for over 20 years, and is the largest herbivorous reef fish in the South Atlantic.[11] Its close relative, the midnight parrotfish (S. coelestinus),[1] has been recorded reaching 31 years of age.[7] Such large bodied and long-lived species are highly vulnerable to over-exploitation by fisheries.[11]
Many species within the genus are sympatric with each other, and often are sympatric with their sister species; Scarus frequently underwent sympatric speciation through adaptive radiation.[1]
Species
There are currently 52 recognised species in this genus:[3]
In Cesare Ripa's Renaissance iconography, the scarus fish symbolised civil "Union," i.e. the joining of individuals into a collective body. Plutarch had written that scarus fish "swim together in shoals and ingeniously and heroically free each other when caught in a net." The scarus thus "denoted reciprocal assistance in the fight for survival."[12]
1 2 Hoey, Andrew S.; Bonaldo, Roberta M. (5 March 2018). Hoey, Andrew S.; Bonaldo, Roberta M. (eds.). Biology of Parrotfishes (1ed.). Boca Raton, FL: CRC Press, Taylor & Francis Group, [2018]| “A Science Publishers book.” | Includeu bibliographical references and index.: CRC Press. doi:10.1201/9781315118079. ISBN978-1-315-11807-9.{{cite book}}: CS1 maint: location (link)
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