KOROR STATE GOVERNMENT MARINE TOUR GUIDE ... - C3

3.5.2 Coral
Characteristics of coral:
Colonies consist of many individual coral polyps
Coral polyps have only a single opening for both food
and wastes
The opening is surrounded by tentacles
Hard corals secrete limestone skeletons
Coral reefs are made up of colonies of individual
animals called polyps. A coral polyp is a simple
jellyfish-like animal living in a cup of limestone
.
Role on the Reef
Coral reef structures are composed mainly of the dead limestone skeletons of previous
generations of corals. Only the thin outermost layer of the reef is alive with colorful coral
polyps. The structures built by corals provide a framework to the coral reef community,
supplying a home for creatures like shellfish, lobsters, crabs, sea stars, and fish.
Feeding
Coral colonies are sessile or stationary. Therefore, they have to catch food that is drifting
by. The stinging cells that cover the tentacles of the corals capture plankton. However,
the main source of food for corals doesn’t come from this prey, but rather from the sun.
Coral polyps live in a symbiotic relationship (benefit from one another) with single-celled
algae called zooxanthellae (pronounced zoo-zan-thel-ee). Zooxanthellae live in the
tissue of coral polyps, and like all plants, they produce food using the sun’s energy,
including sugars and starches. Polyps utilize these products as food. In return polyps
give zooxanthellae a place to live and their wastes to use as nutrients.
Defense
Space is a limited resource on the reef, and corals must constantly fight each other to
survive. There are a number of ways by which corals try to out-compete their neighbors.
Growing over neighboring corals cuts out the precious light needed for their
zooxanthellae. Some species simply digest their neighbors or use long tentacles called
sweeper tentacles to kill others around them.
Reproduction
Colonies of coral start with just one coral polyp. This ‘founder’ polyp reproduces
asexually (on its own) through a process known as budding. The new polyp is
genetically identical to the original polyp. This process is repeated over and over
throughout the coral colony’s life as it increases in size. As hard coral colonies grow,
layers of limestone are laid down and the polyps ‘move’ up to the new layer. The exact
rate at which the coral colonies grow varies amongst species.
Staghorn (Acropora) corals can grow 3-10cm each year with the massive Porites
corals growing an average of 1-3cm per year.
Many corals reproduce sexually just once a year during
a mass spawning. In Palau, it appears from research
conducted by the Palau International Coral Reef
Center that the peak spawning times for most species
of corals are between March and May or September.
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Photo by Kathy Chaston