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Motile organisms

hot button for motile competition part of Biology of Caribbean Coral Reefs hot button for motile-organism space/territory competition hot button for motile-organism food competition hot button for motile-organism mate competition
Competition for mates is considered in this section, while other types of competition in motile organisms can be accessed via the icons.

Motile organisms: mate competition

Most information on mate competition in coral-reef organisms is known for fishes. This section deals first with species of parrotfishes, for which most information is available, with a section on BLUEHEAD WRASSES/HOGFISHES/SERGEANT MAJORS/HAMLETS being found elsewhere.
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of mating blue chromises taken from a video

"Lots of activity here. It's a male blue chromis courting a mate. He'll eventually lead her to a nest-site in his territory, where she'll spawn. Then he'll guard the eggs until they hatch." - Turneffe Island, Belize 2000. Video courtesy Andy Stockbridge, Belize.

NOTE Chromis cyanea


Motile organisms: mate competition: parrotfishes

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a terminal-phase male stoplight parrotfish taken from a video

"Terminal-phase parrotfishes also patrol and defend territory, but with a focus on protecting a harem, rather than a feeding area. Let's follow this stoplight parrotfish for a bit. Any interactions? No... His buzzing about seems aimless, but there's probably purpose to it, if we only knew more." - Cayman Islands 2001

NOTE Sparisoma viride


Males of several species of Caribbean reef fishes, most notably parrotfishes, compete with other males in protecting a harem of reproductively mature females. This involves territorial defense and the male, known as a dominant or terminal-phase male, is kept quite busy. Studies on parrotfishes throughout the Caribbean region show that harems of most species comprise 3-5 females. Van Rooij & Videler 1992 Proc 7th Int Coral Reef Symp 7: 955; Mumby & Wabnitz 2002 Envir Biol Fish 63: 265.

NOTE the life-cycle pattern of parrotfishes begins with a larval fish that transforms to a sexually immature juvenile, and this later transforms into a sexually mature initial-phase individual. These are mostly females, but a few can be males. The initial-phase females comprise a harem that is bossed over by a single photograph of initial-phase stoplight parrotfishterminal-phase male. This male is also known as the dominant male. Should something happen to the terminal-phase male, one of the females changes its sex and appearance and becomes its photograph of terminal-male stoplight parrotfishreplacement. If this seems complex, you should know that it is only part of the story...

stoplight parrotfish Sparisoma viride,
likely a female and
possibly a member
of a harem 0.33X

A terminal-phase (dominant male) stoplight
parrotfish Sparisoma viride 0.33X


photographs of different sexual phases of parrotfishesAbout 40 species of Caribbean fishes are protogynous hermaphrodites, meaning that they start life as females, then change to males. In parrotfishes these "terminal-phase" males compete for females that they keep in harems in defended territories.

NOTE lit. "first female" + "Hermaphroditus", the latter a bisexual Greek deity, referring to both sexes being present in the same body, and with the first expression of sexual identity being as a female. In some species, such as stoplight parrotfishes, the situation is more complex in that some of the juveniles are actually males

  Some other examples of sex-changing coral-reef fishes are (covered in more detail in the section BLUEHEAD WRASSES/HOGFISHES/SERGEANT MAJORS/HAMLETS):
photographs of several sex-changing Caribbean fishes

photograph of a sand tilefish Malacanthus plumieri near its burrowSand tilefishes Malancanthus plumieri are territorial and also keep harems.  They prefer to inhabit open sandy terrain with exposed coral rubble that they can gather and use to construct home burrows.  A male’s burrow defends an area that may encompass up to six or so female burrows.  The females apparently defend their own burrow refuge and surrounding feeding space, and thus space in suitable sand/rubble habitat may be hotly contested.  Males defend their own territories, which appear to be similarly sized whether there be no females or up to 3 females present in a harem.  Baird & Liley 1989 Anim Behav 38: 817.


A sand tilefish Malancanthus plumieri keeps a watchful
eye as it hovers near its burrow entrance 0.5X

  More information on sex-changing development in parrotfishes:
Parrotfish development starts with an EGG being released into the water column by a gravid female, and fertilised with a squirt of sperm by the dominant terminal-phase male... drawing of an egg of a parrotfish being fertilised

...after a few days a LARVA hatches out and spends several weeks or months swimming and feeding in the plankton...

NOTE drawing of 9-mm parrotfish larva adapted from Richards & Leis 1984 p. 542 In, Ontogeny & systematics of fishes. Amer Soc Ichthyol Herpetol

drawing of parrotfish larva
...the larva settles and metamorphoses into a sexually immature JUVENILE, that mostly is a female, but that sometimes can be a male... photograph of juvenile-phase stoplight parrotfish Juvenile phase stoplight parrotfish Sparisoma viride 0.2X

...the juvenile grows into an INITIAL-PHASE, which is usually a sexually mature female, but which may sometimes be a sexually mature male...


Mixed developmental stages of parrotfishes: 2 juvenile
(pinkish coloration) redband parrotfishes Sparisoma
, and several juvenile/initial-phase (white
stripes on black ) striped parrotfishes Scarus croicensis 0.4X

photograph of mixed developmental phases of parrotfishes
...and then transforms into a TERMINAL-PHASE, which is a sexually mature dominant male that tends to a harem of mature females. There is usually only one dominant male per territory. photograph of terminal-phase redband parrotfish Terminal-phase redband parrotfish Sparisoma aurofrenatum 0.3X

photographs of life phases of princess parrotfishes
A terminal-phase princess parrotfish
may be 10 or more years old

photograph of initial-phase stoplight parrotfishA few sexually mature but non-territorial males may lurk at the edges of established territories and try to sneak by the dominant male's defenses for a quick fertilising of the eggs of harem females. In stoplight parrotfishes, these "sneaker" males have the same colour patterns as do the initial-phase sexually mature females, but this may not be the case for other parrotfish species.





Initial-phase stoplight parrotfish Sparisoma
. This one could be a female, as it
was photographed among several like-coloured
individuals in what seemed to be a harem 0.6X

Initial-phase stoplight parrotfish
Sparisoma viride
, sex unknown 0.5X
photograph of an initial-phase stoplight parrotfish
  When a terminal-phase parrotfish dies or disappears, its successor may be one of the harem females or, in the case of stoplight parrotfishs Sparisoma viride, sometimes an outside male. In the first case, one of the females but not necessarily the largest, begins an irreversible change in sex, and withing a few days or a week becomes the new male boss of the harem. The following series shows what we might expect to happen:
photograph 1 in series showing sex change in a stoplight parrotfish photograph 2 in series showing sex change in a stoplight parrotfish photograph 3 in series showing sex change in a stoplight parrotfish photograph 4 in series showing sex change in a stoplight parrotfish photograph 5 in series showing sex change in a stoplight parrotfish photograph 6 in series showing sex change in a stoplight parrotfish
seahorse dive leader for Biology of Caribbean Coral Reef website photograph of an initial-phase stoplight parrotfish taken from a video

"Parrotfishes sure are noisy eaters. Is it marking territory or just getting a bite to eat? Probably the latter, because this initial-phase form is either an immature male, or female, and would likely not be delineating a mating territory." - Cayman Brac 2003

NOTE Sparisoma viride

  photographs of corals scraped by parrotfishes
Some scientists think that the distinctive bite-marks of parrotfishes may serve as territorial markers to delineate boundary lines between the territories of competing males.

drawings showing mock fight between competing stoplight parrotfishesInterestingly, most or all of a stoplight parrotfish's aggression is directed against conspecifics, and practically none against other herbivorous fishes. Border disputes between competing terminal males are mainly ritualistic, involving mock attacks and mouth gaping, but little actual biting. Van Rooij et al. 1996 Envir Biol Fishes 47: 353.

  table of data showing harem and territory sizes in 5 species of parrotfishes from Glover's Reef, BelizeA study on 5 species of parrotfishes in Glover’s Reef, Belize provides data on territory size and harem size (see table). Although the authors suggest that these parameters correlate positively, as would be expected, the data do not support this. For example, the physically small-sized striped parrotfish Scarus iserti has one of the smallest territory sizes of the 5 species, but one of the largest harems. A noticeable feature of the data presented here is the apparently (to a naive reader) small size of territories being defended. For example, the physically largest species Sparisoma viride (max. 60cm length) with an average harem size of 4, defends a territory only 13 x 13m in size. Conversely, the small-sized redband parrotfish Scarus iserti (28cm length) maintains a harem of comparable numbers in an area about two-thirds that size. As expected, as overall density of parrotfishes in a habitat increases, territories generally decrease in size. Mumby & Wabnitz 2002 Envir Biol Fish 63: 265. Photograph of yellowtail parrotfish courtesy Keoki & Yuko Stender, Hawai’i.
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of stoplight parrotfish swimming taken from a video

"You could get dizzy watching a terminal male stoplight parrotfish going about his business.  Here, there, back and forth…what do you suppose he’s doing with all this activity?" - Cayman Brac 2001

NOTE Sparisoma viride


Let's investigate the busy life of a terminal-phase parrotfish. Check the following "duties", mentally sort them into "YES" and "NO" categories, then CLICK HERE to check your answers.

quiz on a terminal-phase parrotfish's daily duties
  photographs of terminal-phase stoplight parrotfishes
Studies on daily time-budgeting of stoplight parrotfishes Sparisoma viride in Jamaica show that a terminal-phases male on the reef crest will spend about 74% of its time swimming or hovering, 9% feeding, and 16% sheltering. Less than 1% of its time is spent on aggressive interactions and, somehat surprisingly in view of the number of times a diver will see it happening, only 0.5% on defecating. Hanley 1984 J Exp Mar Biol Ecol 83: 159.