The
Blue Headed Wrasse is one of the most prevalent fish on coral reefs.
They are often found in schools of hundreds or even thousands, and
besides their unique coloring, they are know for their unique reproductive
strategies and adaptations in the science world.
Distribution
You will find these colorful
fish on coral reefs in Bermuda, the Bahamas, the Caribbean, the Gulf
of Mexico, the northern South Amercian coast, and the Atlantic coast
of Florida.
Food
and Feeding
The diet
of the Blue Headed Wrasse varies, but largely consists of copepods
(small crustaceans), crabs, crab larvae, trematodes (flatworms), zooplankton,
gastropods and gastropod larvae (Norton,
Costello, 1996). Juvenile Blue Headed Wrasse
often act as cleaner fish (Hood).
They also eat plankton found on coral reef’s perimeters.
Physical
Characteristics
A Blue Headed Wrasse
population is composed of three different groups:
1.) the non-sex-changing
primary males, who are small and plain.
2.) the females, who are yellow. Females and primary males are generally
referred to as being in initial phase.
3.) the secondary (or terminal) males, who have blue heads and green
bodies separated by two black stripes (these males were initially
females who went through a sex change (Louch)).
One secondary male
wrasse swimming with harem of females.
Courtesy of
Georgia
State University.
Reproduction/Behavior
Blue
Headed Wrasses are protogynous (female first) sequential hemaphrodites.
This means that when the secondary male in a community dies, the largest
female changes into a male.
Every afternoon, secondary males
gather and wait for females to return from feeding (McIntyre).
Terminal males are pair-spawning. They form “harems” and
mate with only one female at a time. Secondary males experience huge
breeding success. Estimates of breeding range from 25 times an afternoon
(Deloach, 1995) to up to 40 times a day (Louch).
Primary
males have little breeding success. Instead of mating one-on-one,
they release sperm into the water. They must either covertly spawn
with a female or travel in gangs, hoping to catch a female outside
the sight of a secondary male. Often, they gather immediately outside
the spawning sites of the secondary males, hoping to sneak access
to females (Warner).
Accurate portrayal of removal
of secondary male in a population...
The biggest female then changes into a male.
This image courtesy of McIntyre.
Habitat
Once hatched, juvenile fish
have to find protection. Coral reefs provide the perfect habitat for
protection from predators, food, and reproductive practices.
Breeding vs. Habitat
The specifics of breeding are different on large reefs
and on small reefs. The plethora of wrasses found on large reefs enables
primary males to experience high breeding success. The secondary males
are often distracted and not able to constantly monitor females. In
extremely large reefs, where it becomes very hard for males to defend
females, the proportion of primary males in a population can reach
50% and the
amount of secondary males can be as low as 19%.
On
small and medium-sized reefs, there are fewer wrasses and primary
males are very unlikely to have breeding success. Secondary males
control all the favored breeding sites and monopolize mating (McIntyre).
Consequently, the vast majority of wrasses are born female. However,
Blue Headed Wrasses frequently experience socially controlled sex
changes (Louch).
When the secondary male dies or is removed, the largest wrasse (usually
a female, but occasionally a primary male) begins changing color and
within weeks, or even days, transforms completely into a secondary
male (Deloach, 1995).
Coral
Conservation Status
The Blue Headed Wrasse, although
not an endangered species, are prime candidates for becoming endangered
because of the destruction of their natural habitat...coral reefs.
Blue Headed Wrasses are considered "'homebodies'". They
rarely leave the reef from which they were spawned making the protection
of their reef microenvironments crucial to maintaining the numerous
subspecies of Wrasses found on specific coral islands (Clark,
2003).
This image courtesy
of the
National
Action Plant to Conserve Coral Reefs
Conservation
Issues
Coral reefs are one of the greatest habitats for biodiversity
on Earth. They are home to one quarter of all marine plants and animals:
Nearly a million species of fish including the Blue Headed Wrasse,
crabs, eels, mollusks, sponges, worms, grasses, algae, and other marine
animals live on reefs or use them as places to protect their young
(Reef Relief,
2001). Corals also naturally filter seawater for its neighbors. These
reef ecosystems support vast fisheries that people, especially in
coastal nations, depend upon for much of their protein. Barrier coral
reefs can protect shorelines from erosion and storm damage (Reef
Relief, 2001). This ecosystem benefits humans and numerous species.
The protection of coral reefs is crucial for its many species to remain
existent.
Many different abiotic,
and biotic forms of disturbance that affect coral reefs include: coral
bleaching, human harvesting, disease, other human activity, and many
more.
Coral is unique in that it lives a symbiotic life with an organism
called zooxanthellae (zoo-zan-thel-y). Inside the sac of each coral
polyp lives the one-celled algae. The algae gives off oxygen and other
nutrients that the coral polyp needs to live and in return the polyp
gives the algae carbon dioxide and other substances the algae needs.
The algae need sunshine for photosynthesis. That is why coral reefs
grow so close to the surface of the water where it is the sunniest
(Ocean
World, 2003).
When sea temperatures rise or other stresses occur the corals expel
their zooxanthellae. This is called coral bleaching. One environmental
concern is global
warming, as it contributes to increasing water temperatures that
have been connected to coral bleaching (Hall and Hall
2003).
Another concern is
human harvesting. Over fishing can destroy populations of fish that
help keep reefs healthy (Hall and Hall 2003).
Destructive fishing techniques and over-harvesting of fish and tropical
marine life is known to be a worldwide problem (Reef
Relief, 2001). Fishing can be a very positive factor in population
management, but too much of anything can lead to problems.
Diseases such as, Rapid Waste Disease, Yellow Pox Disease, White and
Black Band Disease, and infections such as Aspergillosis (Smith,
2003) can cause large mortality rates in small species habitats. These
diseases can be caused by any number of different things, generally
stemming from bacteria in the water.
One may not think that what occurs on land can affect the ecosystems
within the ocean, but it does. Agricultural run-off that contains
pesticides and fertilizers add toxins and nutrients to reefs that
require nutrients-free waters to thrive. Over-development and lack
of sewage and storm water infrastructure in coastal areas is also
a leading source of damage to reefs. Humans also play are more direct
role in the destruction of coral reefs. Divers and snorkelers touch
and step on the reef, breaking it. Boat groundings and propellers
damage corals and sea grasses, along with many other species (Reef
Relief, 2001).
As humans we need to be more aware of our surroundings and what we
can do to ensure their stability. So next time you’re snorkeling,
DON’T STEP ON THE REEF!
Literature
Cited
Costello,
M.J. 1996. Development and future of cleaner-fish technology and other
biological control techniques in fish farming. 171-184 in M.D.J.
Deloach, N. 1995. Reef fish behavior. Jacksonville:
New World Publications.
Hall, Howard and Michele Hall. 2003. Sixty Fathoms Under the Sea.
National Wildlife: World Addition 41(3):52-56.
Hood
College. Date Unknown. Thalasoma bifasciatum.
http://www.hood.edu/academic/biology/blueheadwrasse.htm
Accessed 2003 April 3.
Louch,
C. Date Unknown. Fish Tales. http://www.ptmsc.org/html/fish_.html
Accessed 2003 April 3.
McIntyre,
K. Date Unknown. Sex change you say???
http://icarus.cc.uic.edu/~aperry4/bluehead.html
Accessed 2003 April 3.
Norton,
S. Date Unknown.Bluehead wrasse. Fishes of North Carolina Rock
and Wreck.
http://core.ecu.edu/biol/nortons/NCFishes/BonyFish/Labridae/Bluehead/BlueheadWrasse.html
Accessed
2003 April 3.
Oceanworld. 2003.
Coral Reef Destruction and Conservation. http://oceanworld.tamu.edu/students/coral/coral5.htm
Accessed 2003 April 3.
Reef Relief. 2003. All About the Coral Reef http://www.reefrelief.org/library.html.
Accessed 2003 April 3.
Sayer,
editor. Wrasse: Biology and use in aquaculture. Oxford: Fishing News
Books.
Smith,
Garriet. 2003. The Decline of the Coral Reef- Coral Bleaching and
Diseases with Dr. Garriet W. Smith http://www.accessexcellence.org/LC/ST/st6bg.html
Accessed
2003 April 3.
Global Warming:
Early Warning Signs.1999.http://www.climatehotmap.org/references.html
Accessed 2003 April 3.
(top)
Images
Cited
http://www.coris.noaa.gov/activities/welcome.html
http://icarus.cc.uic.edu/%7Eaperry4/bluehead.htm
http://www.motherjones.com/coral_reef/science.html
http://oceanworld.tamu.edu/students/coral/coral5.htm
http://nature.org/joinanddonate/rescuereef/
http://www.sciencenews.org/20010825/bob9.asp
http://scubadiving.com
http://www.wadespage.com/index.shtml
http://core.ecu.edu/biol/nortons/NCFishes/BonyFish/Labridae/Bluehead/BlueheadWrasse1.html
http://core.ecu.edu/biol/nortons/NCFishes/BonyFish/Labridae/Bluehead/BlueheadWrasse2.html
http://www.gsu.edu/%7Ebiomgx/lab/organisms/bluehead/bifasciatum.htm
http://www.coris.noaa.gov/about/hazards/hazards.html
Authors:
Corliss Harris, Melissa
Maheux, Emily
Shepard
Creation/revision date: 31 March 2003
Courtesy of 
