REEFS: FREQUENTLY ASKED QUESTIONS
What Is A Coral?
Despite the fact that corals look more
like rocks or plants, they are definitely animals. Coral
colonies are composed of many tiny, cup-shaped animals
called polyps, which are related to jellyfish. A single
coral polyp may be as large as a saucer or smaller than
the head of a pin. Millions of polyps working together
in a cooperative colony generation after generation
create the limestone skeletons that form the framework
of the beautiful coral reef.
How Do Corals Start Out Life?
Corals begin life in tropical waters
as free-floating larvae. After a relatively short period
of time, the larva eventually attaches itself to a hard
surface and becomes a polyp. Polyps divide asexually
and form colonies. Coral colonies reproduce both sexually
and asexually. In sexual reproduction, the coral polyps
release both eggs and sperm into the water. (This is
also known as coral spawning.) One type of asexual reproduction
occurs when fragments of coral are broken off as a result
of storm action. The broken pieces of corals usually
survive and continue to grow and produce a new colony.
This process is referred to as “fragmentation”.
What Do Corals Eat?
A coral polyp consists primarily of tentacles,
a mouth and a gut (think upside down jellyfish). Many
corals are passive feeders on plankton. Most corals
also get nutrition from microscopic algae (zooxanthellae)
living within their tissue. Coral polyps are generally
nocturnal feeders and are provided sugars made by their
photosynthetic zooxanthellae during the day.
Where Does The Framework Of A Coral
Reef Come From?
Corals extract calcium and carbonate
from seawater to build an inner skeleton that is external
to the coral. This external skeleton lies underneath
a thin layer of tissue. Over the years millions of coral
polyps in colonies create the framework of the coral
reef. Coral reefs grow very slowly. It may take up to
a hundred years for a coral reef to grow one meter (around
What Is The Difference Between Hard
And Soft Corals?
Hard corals, also called reef-building
corals, produce a rock-like skeleton made of the same
material as classroom chalk (calcium carbonate). These
skeletons and the various shapes of different colonies
form the familiar structure of the reef. Hard corals
rely on symbiotic algae (zooxanthellae) living within
their tissues for nutrition and energy to build their
skeleton. They must therefore live in shallow clear
water to allow sunlight to reach the algae. Soft corals
look like colorful plants or graceful trees and are
not reef-building since they do not produce the hard
calcified skeleton of many reef-building corals. However,
soft corals do produce smaller amounts of calcium carbonate
that help them keep their shape. Soft corals can be
distinguished from hard corals by the fact that soft
coral polyps always have eight tentacles, while hard
coral polyps have multiples of six tentacles.
What Is Symbiosis?
Symbiosis is defined as the close association
between two or more interacting organisms, usually of
different species. The relationship is usually classified
as belonging to one of three types: mutualism (benefiting
both partners), parasitism (one partner, the parasite,
benefits, at the expense of the host), or commensalism
(one partner benefits while the other is unaffected).
Changes in the physical environment such as the amount
of sunlight or salinity, or the temperature, and in
the biological community, such as the presence or absence
of other organisms and how they interact with the symbiotic
pair, may change the nature of the symbiotic relationship
from one type to another. Like organisms, symbiotic
relationships are responsive to the environment and
can change over time.
What Is The Largest Coral Reef In
As the name implies, the Great Barrier
Reef, located off Australia’s East Coast is the
largest coral reef in the world. This enormous reef
is over 2023 kilometers (1257 miles) long and covers
more than 300,000 square kilometers (about 186,000 miles).
Home to more than 1500 species of fish, dolphins, whales
and sea turtles, the Great Barrier Reef is actually
a collection of more than 3000 smaller reefs. The second
largest reef lies off the coast of Belize, in Central
What Are The Main Types Of Coral Reefs?
Reefs are generally classified into the
following three types:
|| Fringing reefs,
the most common type of reef, form along a coastline.
They grow on the continental shelf in shallow water.
grow parallel to shorelines but are farther from
shore and are usually separated from the land by
a deep lagoon. They are so called because they form
a barrier between the lagoon and the seas, protecting
||Coral Atolls are rings
of coral reef growing on top of old sunken volcanoes
in the ocean. They begin as fringing reefs surrounding
a volcanic island; then, as the volcano sinks, the
reef continues to grow, and eventually only the
reef remains. There are over 300 atolls in the South
Pacific. Atolls contain islands.
Do Any Animals Eat Corals?
One of the most important predators of
corals is the Pacific Ocean’s Crown of Thorns
Sea Star. It is estimated that a single Crown of Thorns
Sea Star can eat from 2 to 6 square meters (6 to 20
square feet) of corals per year. Many fish species such
as parrotfish, butterfly fish and tangs also include
corals as part of their diet. Attentive divers and snorkelers
hear the crunch of hungry parrotfish as they chew up
their delectable meal that includes the skeleton. Other
coral predators include some types of marine snails
and marine slugs, known as nudibranchs. Interestingly,
these coral predators digest the animal tissue and release
the symbiotic algae (zooxanthellae) in their feces.
The nudibranchs may also keep the nematocysts (stinging
structures) and symbiotic algae for their own nutritional
Why Are Coral Reefs Important To Humans?
Coral reefs are among the most biologically
diverse ecosystems on earth. Second only to tropical
rain forests in the number of species they harbor, they
are sometimes called the “rainforests of the sea”.
Although coral reefs only occupy about 0.07 percent
of the ocean floor (an area roughly the size of Texas),
they are home to as many as one quarter of the world’s
marine species. Coral reefs offer important income sources
for their human neighbors through tourism and fishing,
which provide both subsistence and trade. Recently,
scientists have begun to discover that coral communities
may contain valuable medicines that may one day lead
to treatments for cancer and HIV. For coastal communities,
coral reefs also play an important role in protecting
their coastlines from storms.
Why Are Coral Reefs In Danger?
Coral reefs are among the most beautiful
ecosystems in the world but are also among the most
susceptible to human impacts and are damaged or destroyed
with alarming ease. Practices such as over-fishing,
the use of dynamite or poison to capture fish and dropping
boat anchors on corals have produced enormous damage.
Even an accidental touch from divers and snorkelers
can significantly damage the delicate coral polyps.
Pollution, silting from land-based construction, and
fertilizer runoff have led to damage to coral reefs
worldwide by blocking the sunlight corals require for
photosynthesis by their symbiotic algae. Rising sea
temperatures from global warming can also destroy corals
by ending the symbiotic relationship with zooxanthellae.
Hurricanes and earthquakes, which can also lead to significant
damage to the reefs, are nonetheless generally viewed
as a natural cycle of the ecosystem. However, when a
coral reef has been damaged from human effects, it may
have a more difficult time recovering from natural disasters
such as hurricanes and earthquakes.