Bluehead Wrasse | Oceana
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Ocean Fishes

Bluehead Wrasse

Thalassoma bifasciatum

Distribution

The Caribbean Sea and adjacent waters, including Florida, Bermuda, and the Gulf of Mexico

Ecosystem/Habitat

Coral reefs

Feeding Habits

Foraging predator

Conservation Status

Least Concern

Taxonomy

Order Labriformes (wrasses and relatives), Family Labridae (wrasses and parrotfishes)

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The bluehead wrasse is a small-bodied wrasse that lives on coral reefs of the Caribbean Sea and its adjacent waters (Florida, Bermuda, and the Gulf of Mexico). As a result of its interesting mating system (discussed below), the bluehead wrasse is one of the best-studied reef fishes on Caribbean reefs.

It gets its common name from the adult coloration, which includes an obviously blue head on an otherwise green body.  Juveniles are solid yellow, or nearly so, with a black spot on the dorsal fin.  The numerical success of the bluehead wrasse is apparent to anyone who has visited a Caribbean reef; it is one of the most common species in that region.

Bluehead wrasses are generalist foragers and eat a variety of prey.  They are known to forage for small invertebrates and crustaceans on the reef surface, target individual zooplankton in the water above the reef surface, and clean the parasites off of larger species.  As they are one of the most common small-bodied fishes on reefs, bluehead wrasses are eaten by many different species of predatory fishes. 

The bluehead wrasse’s complex mating system has been a topic of scientific study for decades.  This species reproduces through a behavior known as broadcast spawning, where females release eggs and males release sperm into the water column above the reef, at the same time.  This method increases the likelihood that eggs will become successfully fertilized and that fertilized eggs will not be eaten by egg predators on the reef surface.  All bluehead wrasses hatch as females.  As they mature, some individuals become male.  Young (though mature) males continue to resemble females in appearance and participate in group spawning with large groups of females and other males.  As they continue to mature, the largest males transition into the so-called ‘terminal males,’ when they finally develop the blue head and green body.  These largest males defend territories and develop harems of females with which they spawn one at a time.  Spawning still requires the broadcast method described above, but the terminal males prevent (via aggressive behavior) other males from participating.  As a result of these transitions, bluehead wrasses may reproduce in four different ways throughout their lifetime:  1) as a female in a group spawning event; 2) as a female in a pair spawning event within the territory of a large male; 3) as a small male in a group spawning event; and 4) as a dominant, terminal male in a pair spawning event within its own territory.  Interestingly, small males release more sperm than large dominant males because their sperm must compete with that of other males, while a dominant male competes with other males before (rather than during) spawning.

The bluehead wrasse is too small to be eaten but is captured for display in public and private aquaria.  Currently, scientists do not believe that the species is at any risk of extinction, and population sizes are apparently stable.  However, it is important to continue to monitor bluehead wrasse populations in order to ensure that any changes resulting from capture of adults or from expected negative trends in coral reef health throughout its range will be identified at an early stage.

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Additional Resources:

http://www.iucnredlist.org/details/187652/0

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