#wrasses

A ringtail Maori wrasse (Oxycheilinus unifasciatus) in Honaunau Bay, Hawai'i

A juvenile California sheephead (Bodianus pulcher) in Channel Islands National Park, California, USA

A female Pacific bird wrasse (Gomphosus varius) in Tahiti, French Polynesia

Though this individual is female now, bird wrasses undergo sequential hermaphroditism, and may become male later in life

Once in a Blue Moon: The Bluehead Wrasse

The bluehead wrasse (Thalassoma bifasciatum) is a small species of wrasse found only in the western Atlantic Ocean; particularly around the Caribbean and the northern coast of South America. They inhabit coral reefs, and occasionally along sandy bottoms and sea grass meadows. Bluehead wrasse prefer shallow, warm, clear water and reefs with lots of hiding places that they can easily access.

T. bifasciatum is noted for its bright coloration. Females and small males are bright yellow with a white underbelly, while larger males have a greenish body and a blue head, seperated by thick black and white stripes. These large males are typically 7-8 cm (2.7-3.1 in) in length, while smaller males and females are around 6 cm (2.3 in).

Like many coral reef fish species, the bluehead wrasse engages in protogyny. All eggs hatch as females, and as they mature some change into males. These young males, known as initial phase (IP) males, continue to resemble females but are fully capable of reproduction. Eventually, the largest of them transition into a secondary phase, also known as the terminal phase (TP). TP males carry the characteristic blue and green markings of bluehead wrasse, and are significantly larger. The transition from female to IP, IP to TP, or even directly from female to TP can occur at any time, and is particularly triggered by removal of dominant (TP) males from a population.

Reproduction typically occurs from January to August, though it can continue sporadically throughout the year. Mature adults participate in group spawns, in which females and both male types converge at spawning sites. Males compete for proximity to females, and typically TP males will closely guard access to a harem of 30-50 females, while IP males will attempt to use their coloring to sneak in and mate surreptitiously. T. bifasciatum are broadcast spawners; both sexes release their gametes into the water column, where they are fertilized and carried away by the current.

Eggs spend 6-8 months free floating, sometimes drifting miles from their spawning grounds. After hatching into juveniles (larvae), they burrow into the sand and remain there for several months before emerging to seek out a coral reef in which to shelter. At this point, a year after hatching, they are typically mature and ready to mate themselves. Individuals can live up to 3 years in the wild, though juvenile mortality is high.

Bluehead wrasse are cleaner fish. The majority of their food are parasites picked off of larger fish, as well as shrimp, krill, crustaceans, and plankton gathered from the coral itself. However, they are also often food themselves for larger fish, moray eels, and stingrays.

Conservation status: The IUCN considers the bluehead wrasse to be Least Concern. Their primary threat is habitat loss due to coral reef bleaching.

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Photos

Doug Perrine

Terence Zahner

A male slingjaw wrasse (Epibulus insidiator)

Let's Hear it for the Humphead Wrasse

The humphead wrasse, Cheilinus undulatus, is also known as the Māori wrasse, Napoleon wrasse, or the blue- tooth grouper. They can usually be found around coral reefs and steep rocky cliffs in the Indo-Pacific, particularly on the east coast of Africa, the west coast of India, and the tropical waters of southeast Asia and the Great Barrier Reef.

The Māori wrasse gets its name from the distinctive markings that adults carry. Males are blue-green or purple, while females are more often red or orange. Both have unique patterns of lines and dots covering their heads, and stripes running down the rest of their body; early researchers compared the patterns on their heads to the tattoos traditionally used by the Māori people. In addition to its striking coloration, C. undulatus is also known for being the largest member of the wrasse family. Males can reach up to 2 m (6.5 ft) long and weigh up to 180 kg (396 lbs), while females tend to be smaller. Males also have a large 'hump' on their foreheads, hence the name humphead wrasse.

Another feature of note in C. undulatus is the set of large teeth fused into a parrot-like beak. They use this beak to predate upon hard-shelled animals like mollusks, urchins, sea stars, and crustaceans. On occasion, they also feed on smaller fish and moray eels. Due to their size, adults have very few natural predators aside from sharks, but larvae and small juveniles are more often opportunistically hunted by other fish.

Like many coral reef fish, the humphead wrasse is a protogynous hermaphrodite. This means that most individuals begin life as a female, and become male later in life-- known as 'super males', they are larger than males who did not transition. Individuals first become sexually mature at 5-7 years old, and females begin transitioning to male at 9-12 years old. Spawning occurs a few times a year, and during this period over a hundred adults can congregate in an area. The female releases about 20 eggs into the water column, where they are fertilized by her chosen partner. Three to four weeks later, the eggs hatch and the larvae migrate to the nearby reef.

Conservation status: C. undulatus is considered Endangered by the IUCN. Populations have declined due to overfishing and by-catch mortalities, loss of their food sources, habitat destruction, and capture of juveniles for the aquarium trade.

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Photos

Andrew J. Green

Lluís Masuet