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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 part of competition deals with bluehead wrasses and hogfishes/sergeant majors/hamlets in 2 sections to follow, with a larger section on PARROTFISHES 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: bluehead wrasses

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of bluehead wrasse with members of his harem taken from a video

"Let’s follow this terminal-phase bluehead wrasse. Busy guy! Has to monitor the females, grab a bite to eat.  Now he heads off, perhaps into someone else's area...although we don't see any confrontations. Maybe the other males are all just as busy. " - St. Maarten 2005

NOTE Thalassoma bifasciatum


photograph of life-phases of bluehead wrasses
Like parrotfishes and many other reef fishes, bluehead wrasses are also protogynous hermaphrodite, but the terminal-phase males defend territories only loosely or not at all, and they do not generally have harems. The groups of initial-phase individuals commonly seen bustling about the reef consist predominately of sexually mature females (capable of transforming into terminal-phase males) along with a few sexually mature males. The largest of these may also be capable of transforming sexually. Warner 1987 Anim Behav 35: 1470; DeLoach 1999 Reef fish behavior New World Publ, Florida.

NOTE a sex-changing species that starts out as a female, then changes to male


photograph of bluehead wrasses feedingDuring daily spawnings, initiated and controlled by a terminal-phase male, some sexually mature initial-phase males may try to join the spawning group and release their own e, and for this reason are policed from the area by the terminal-phase male. Other terminal-phase males who similarly attempt to compete are also chased away. DeLoach 1999 Reef fish behavior New World Publ, Florida.

NOTE these particular males have identical colour patterns to those of the females and, by their attempted clandestine sexual activities, are known as "sneakers"


Initial-phase bluehead wrasses Thalassoma bifasciatum
feed on zooplankton and also act as cleaners of other
fishes, while terminal-phase males tend to feed on small
bottom-dwelling or bottom-swimming invertebrates 0.1X


photograph of a group of bluehead wrassesA territorially dominant terminal-phase bluehead wrasse will fertilise dozens of egg-spawnings per day, while nearby males who are less aggressive, and thereby less successful in recruiting females, may service only a few or none at all. Spawnings of these more recessive males are also at risk of sperm-dilution from sneaker males who work the fringes.

This mixed batch of bluehead wrasses Thalassoma
includes several initial-phase individuals
and a single terminal-phase individual (lower R). The
wrasse on the middle-Left appears to be undergoing
transformation to a terminal-phase male. Such
transformations, usually from the largest initial-phase
female, can begin within minutes of the removal of a
terminal-phase male and are finished in about a week.
Warner & Swearer 1991 Biol Bull 181: 199.



Motile organisms: mate competition: hogfishes/sergeant-majors/hamlets


photograph of Spanish hogfish
Spanish hogfishes Bodianus rufus are also protogynous hermaphrodites, changing sex during their lifetime from female to male. The mature males maintain up to 20 females in harems in well-defined territories. Aggression between males at territorial boundaries is common and involves chasing, mouth-to-mouth pushing, and sometimes jaw-biting. Rocha 2000 Coral Reefs 19: 184.



This Spanish hogfish appears to be
changing sex from female to male 0.2X

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of egg mass of sergeant-major taken from a video

"Oh, this is interesting! It's an egg nest of a sergeant-major on the side of this wreck. And there's its owner, all dark and mad because we've come near. The eggs are red in colour if you see them near the sea surface. The male will guard the eggs for about a week until they hatch into little larvae." - Aruba 2004

NOTE Abudefduf saxatilis


photograph of sergeant-major tending its eggs
Male sergeant-majors become dark in colour when courting a female, nest-building, and defending both female and nest. The spawning nest does not seem like much, often just a flat area, sometimes vertical, but cleaned of all loose objects and growths. Females, often several in succession, are led to the nest and encouraged to spawn their eggs. The eggs, up to about 20,000 per female, are sticky and adhere to the substratum. Periodically, the male with release sperm onto the nest. The male will guard the nest for about a week until the eggs hatch into tiny larvae and swim off into the plankton. DeLoach 1999 Reef fish behavior. New World Publ, Inc., Florida.


Male sergeant-major Abudefduf
with eggs 0.25X


photograph of indigo hamletColour patterns of hamlets are variable, and it is thought that only identical colour-morphs of a species will mate. Hamlets are simultaneous hermaphrodites, meaning that each individual can produce either eggs or sperm at any given time. During spawning bouts, which can last for hours, a given fish may switch sexual roles several times, alternately releasing eggs, then sperm. DeLoach 1999 Reef fish behavior. New World Publ, Inc., Florida.




Indigo hamlets Hypoplectrus indigo vigorously compete
for mates, but the accustomed scenario of males
competing for females is made more complex by the
abrupt alternations in sex of the participants 0.5X



photograph of two indigo hamlets
Courtship in hamlets Hypoplectrus spp. is most vigorous in the member of the pair whose turn it it to spawn eggs, and this individual displays last before a mating act. Egg- and sperm-trading by members of a mating pair in this way are thought to increase the probability of the eggs being fertilised and to increase the fidelity of the pair-bonding. Fischer 1987 Envir Biol Fishes 18: 143.


Indigo hamlet Hypoplectrus indigo 0.25X