The ecologically diverse coral reef
at our backdoor is home to over 4,000 species of fish. All these species
play a role in the reef ecosystem; some fish provide food for other
animals, while others clean damaging algae from the reef. Still other
species have symbiotic relationships with other fish, a relationship in
which both species benefit. One of the most striking examples of
symbiosis involves the cleaner wrasse. This fish is responsible for
setting up what are known as "cleaning stations," providing a valuable
service to other fish by picking off and "cleaning" its customers of
parasites and dead tissue. The wrasse, in turn, receives nutrients from
the parasites and tissue.
The parasites that the wrasse consume are organisms
that live on or within the body of a host, in this case a fish. Often,
parasites are simply small crustaceans that live between the scales of
fish and feed on its tissue. It is not known whether these critters,
which are a fact of life for many fish, are anything more than an
annoyance, but it is clear that most fish prefer to have them removed.
For this removal, many fish turn to the cleaner wrasse to get the job
done.
The cleaner wrasse, one of 600 species of wrasse, is
found along coral reefs worldwide and usually choose a home along the
reef that is popular among fish to set up its cleaning station. At this
location, various fish literally line up and wait to be "cleaned" by the
wrasse. This is one of the few cases in which varying species of fish
actually inhabit the same space without becoming territorial or
aggressive with each other. It's clear that these fish have one thing on
their mind when they line up at the cleaning station: getting the
parasites removed as soon as possible. Easily distinguished by a bright
blue and yellow band, the cleaner wrasse makes an effort to advertise its
services by performing a dance. Likewise, when a fish wants to be
"cleaned" it sends specific signals to the wrasse, such as keeping its
body stationary, while spreading its fins and gills and opening its
mouth. If the wrasse picks up on the signal it will begin the cleaning
process on its customer, which is usually a larger fish. Cleaning
consists of the wrasse swimming over the entire body of its customer,
eating parasites from the fins and gills. The wrasse will even go inside
the mouth and clean between the teeth of its customer. Interestingly
enough, the wrasse is rarely injured or eaten by the other fish; the
wrasse vibrates its fins while cleaning to remind its customer of its
presence. Moreover, the cleaned animal will frequently defend the
cleaning station and its cleaners from attack by would-be
predators.
Almost all marine species are
actively involved in close symbiotic relationships with at least one
other species in their community. The unique relationship between the
cleaner wrasse and the fish it cleans at the "cleaning stations" are an
important and impressive example of symbiosis. Not only does the
satisfied customer leave parasite free, but also the wrasse enjoys a
protein rich meal.
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