This is a (very) rough draft of an article on parrotfish I have been working on for the EoE.
Introduction
Parrotfishes (Family
Scaridae), who get their name from 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. They also have considerable ecological
impacts on coral reefs through herbivory and bioerosion .
Morphology
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 scales , usually with 22-24 scales along the lateral line.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 . 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.
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.
Distribution
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.
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 cretensis, are common
over rocky reefs of the Gulf of California and Mediterranean Sea, respectively.
Feeding Behavior
Parrotfishes are primarily herbivorous, grazing intensively
on dead, algae-coated coral, vegetable material, and in some species sea
grasses. Bolbometlopon muricatum, 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 Acanthuridae, parrotfishes
form large feeding groups, sometimes with multiple species, to overwhelm
territorial fishes and deter predators.
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. 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
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.
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 Labridae. After creating a hole in
the sand Cryptotomus then produces its mucous nightgown.
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.
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 croicensis, exhibit a wide range of
reproductive behaviors depending on the area in which they are found. In
Panama, Scarus croicensis 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 croicensis
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.
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. There is no evidence of parental behavior in
parrotfishes.
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.
Associations
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 Bolbometapon muricatum determine the fine-scale topography of
coral reefs.
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.
Conservation Status
One scarid, Scarus guacamaia
(rainbow parrotfish), is listed as vulnerable to extinction. (The World
Conservation Union, 2002)
Powerpoint Presentation (ID)
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