Coral reefs

This essay has a total of 3845 words and 17 pages.

coral reefs


Coral reefs are one of the oldest types of living systems on earth, and certainly one of
the most spectacular (Goreau, 1987). They are massive underwater structures formed by the
limestone skeletons of tiny invertebrate animals. Reefs house a greater diversity of body
forms, chemistry, and animal phyla (thirty-two compared to the eight that inhabit the most
biodiversity ecosystems on land). Phyla comprise the second largest category of living
things, after kingdoms.

Coral animals begin life as free-floating larvae, but settle on the sea floor in sedentary
colonies. The term "coral" applies both to these animals and to their skeletons,
particularly the skeletons of stone-like corals (Discover 1997).

Many different organisms, including mollusks, sponges, and worms, help shape reefs, but
hard corals and various algae are the major architects. In effect, the corals build
limestone, because their skeletons are made of Calcium Carbonate. The skeletons deposited
by these corals and other organisms accumulate, along with sand and other debris, to form
the backbone of the reef. Over tens of thousands of years, chemical and mechanical changes
turn the reef into true rock (Alstyne and Paul, 1988).

The body of a coral animal consists of a polyp, which is the living portion of the coral.
A polyp is a hollow, cylindrical structure attached at one end to a surface, the other end
is a mouth surrounded by tentacles, which gather food and can sting prey to paralyze it.
Polyps live in colonies, which grow from 1 to 7 inches, depending on the species. Coral
polyps are classified as animals. Microscopic algae live within the animal tissues in a
symbiotic relationship. The algae turn sunlight into carbon and sugars, which are then
available to the polyp. In turn the polyp filters particles out of the water and excretes
waste (nitrogen and phosphorus) that becomes available to the symbiotic algae. It's this
very tight nutrient recycling within the coral itself that allows these corals to live in
very low nutrient waters.

There are three kinds of reefs: atolls, barrier reefs, and fringing reefs. Atolls are
formed out in the middle of the ocean by volcanic subsidence, while fringing and barrier
reefs form near continents. Florida contains both of these kinds of reefs, not as far
offshore as Australia's Great Barrier Reef, but not terribly close either. Most are eight
to eleven kilometers (five to seven miles) offshore. All three kinds of reefs can have
associations, called patch reefs, which are small, shallow-water clusters or offshoots. In
Florida, patch reefs can be as close as one hundred meters to the shore. Ancient limestone
reefs have occupied the Florida peninsula intermittently over the past 150 million years
(Discover, 1997). Florida's present coral reefs came into existence 5,000 to 7,000 years
ago, when sea levels rose following the Wisconsin Ice Age. The reefs in the Florida Keys
are part of the third largest barrier reef system (360 square kilometers from Miami to the
Dry Tortugas).

Coral reefs are continuously being both built up and decomposed, so different parts of a
reef are in varying stages of succession (Richmond, 1993). Coral reefs are very fragile,
because reef-building organisms cannot thrive if the surrounding water changes
significantly. Coral reefs require very specific conditions in order to grow: a solid
structure for the base; warm and consistent water temperatures (averaging between 20 and
30 degrees Celsius); stable salinity; moderate wave action; and clear water that is low in
nutrients and plankton. The water on a healthy coral reef is clear because there are very
few nutrients, so plankton that would cloud the water are few. In general corals grow
slowly, but they are extremely efficient at living and reproducing in these conditions
(American Zoologist, pg 524-536).

Reefs matter in many ways:
• Links to other coastal ecosystems: such as mangroves and sea grasses.
• Sources of medicine: Because corals and most other reef-dwelling species move
either very little or not at all, they rely on biochemical warfare for both offense and
defense. They have developed strong and very diverse chemical compounds, and a number are
proving to have significant anticancer, antibacterial, antiviral, and anti-inflammatory
properties. For example, cytarabine, derived from the Caribbean sponge Tethya crypta,
induces remission in certain forms of leukemia and is also useful against the herpes
virus; pseudopterosins from the Caribbean sea-whip Pseudopterogorgia elisbethae have
powerful anti-inflammatory and analgesic properties; and prostaglandin's, which have a
wide range of clinical applications, can be found in large quantities in the Caribbean sea
fan Plexaura homomalla (Alstyne and Paul, 1988). About six thousand unique chemical
compounds have been isolated from reef organisms so far, and this potential pharmacopoeia
has barely been tapped. Coral, which is porous and quickly reabsorbed, is used to repair
human bone, with no risk of implant rejection or transmission of infection.

• Living breakwaters: Reefs protect coastal areas from storms, floods, and erosion.
They are the key to many a surfer's "perfect wave," and contribute sand to the growth of
beaches.

• Evaporation basins: Reef flats and lagoons may play a key role in regulation of
the sea's salt content, removing salt by acting as evaporation basins.

• Shapers of landmass: Reefs play a part in the formation of tropical islands
through deposition and accumulation of Calcium Carbonate rock (limestone) and sand.

• Mediators of global climate: Corals remove large amounts of carbon from the
atmosphere as they grow, actually "fixing" 700 billion kilograms a year. Carbon dioxide is
a greenhouse gas that contributes to global warming.

Coral Reefs are also very important to the Florida economy:
• Recreation and tourism: tourists spend about $1.2 billion annually in the Florida Keys.
• Food fisheries: the value of reef fisheries (including shellfish and other
invertebrates) off the Keys is estimated at $48.4 million.

• Other industries: reefs support a large trade in aquarium fish and are a habitat for sport fish.
Most present-day reefs have probably been growing for 5,000 to 10,000 years. But their
continued survival is now threatened. Reefs around the world are now declining at an
unprecedented rate--one that far outstrips our understanding of the problem (Cousteau,
1985). Few long-term studies of coral reefs have been conducted, and there is considerable
debate about the overall health of reef ecosystems. Still, most scientists agree that
reefs worldwide are in crisis. Caribbean reefs appear to be in worse condition than
Pacific reefs. They naturally have lower levels of biodiversity, which makes them more
vulnerable to structural change. They house significantly fewer species of fast-growing
and reef-building corals, and diseases have affected the entire basin while the far
greater size of the Pacific has tended to keep outbreaks reef-specific or regional. The
third largest barrier reef system in the world is located off the Florida Keys. Its recent
decline has been attributed to multiple causes, almost all of which involve human
activity. Most scientists agree that the greatest threat to Florida's reefs is degraded
water quality, when land is cleared for development or agriculture, fertilizers,
pesticides, and eroded soil wash out to sea when it rains. Pesticides can weaken the
corals and make them more susceptible to disease. Sediments can smother or scour the reef,
impairing coral growth. The sea is also where most of the sewage and wastewater from
Florida Key residents and their one million annual visitors ultimately end up, and this
pollution also degrades the water quality. In particular, fertilizers and sewage have
significantly increased the level of nutrients in the water of Florida Bay. As a result,
phytoplankton utilizes these nutrients and grows exponentially. This causes various kinds
of algal blooms: phytoplankton turning the water green, toxic blooms including red tides,
and macro-algae overgrowing and smothering the reef. As phytoplankton increases, so does
the turbidity of the water. This cuts down the amount of light reaching the zooxanthellae
(tiny one-celled algae that live inside coral polyps), so photosynthesis within the coral
is adversely affected.

Poor water quality affects other parts of the coastal ecosystem. Coastal ecosystems act as
buffers between land and sea, reducing negative impacts in both directions. When stressed,
they are less effective. There are three key environments in Florida that are intimately
related. First of all, the mangroves along the shore, secondly, the grass beds in shallow
water, and finally, the coral reefs at the edge of the shelf. Water flows through this
system, and the health of each system determines the health of the next. Every time
somebody cuts down mangroves, it affects the sea grass beds somewhat further off shore.
Every time a sea grass bed is destroyed, it affects the coral reef even further off shore.
So all these interconnected habitats need to be preserved as a whole. Increased nutrients
in the water were blamed for a major sea grass die-off in the bay in 1987, further
stressing the reefs.

Silt normally held down by the sea grass flowed out of the bay and ended up on the coral
reefs, clouding the water. This sediment hurts the reef in several ways: it impairs
photosynthesis; it forces corals to expend energy cleansing themselves; and it can even
bury them entirely. Studies showed corals only 4 kilometers from each other grew at
dramatically different rates: the corals closer to Florida Bay grew only half as much as
offshore corals.

The location of the Florida Keys makes them particularly vulnerable. They are close to the
heavily populated North American coast, and ocean currents place them downstream of the
Caribbean basin. The Loop Current, which travels clockwise in the Gulf of Mexico from the
Yucatan Peninsula, to the Mississippi River, by Tampa Bay, and ultimately to the Florida
Keys, carries storm water and agricultural runoff containing pesticides, heavy metals,
oil, and other toxic waste from more than half of the United States. Even sediment from
the Amazon finds its way through the Florida straits. Compounding the problem is the fact
that most of the bedrock underlying the islands of the Florida Keys is highly porous
limestone, the remains of ancient reefs, through which contaminated waters easily flow in
and out. Preliminary studies indicate that ground waters beneath the reefs do contain
nutrients, principally ammonia, at levels many times higher than that of normal seawater.
These nutrient-rich ground waters can seep into the reef's water columns with each change
of the tide.

People harm reefs in lots of other ways:
• Over fishing: fish and other reef species are caught by subsistence fishermen and
over harvested by commercial ones. This has reduced overall populations, and specifically
that of certain fish that control algae on the reefs. Destructive fishing practices also
harm reefs badly. These include using crowbars to dislodge clams, abalone, and other
marine invertebrates from reefs at low tide, and also the illegal use of explosives and
cyanide poisoning

• Ship groundings: thousands of ships and boats have run into Florida's reefs since
colonial times. Evidence is mounting that reefs struck frequently by boats recover more
slowly from storm damage than untouched reefs.

• Collecting of coral and other reef species: specimens are collected live for
aquariums or for curios and jewelry.

• Mining of coral rock and sand: These are used for building materials, and coral is mined for jewelry.
• Redirecting water flow: Cross-sections of Florida reefs show that they began to
decline beginning about eighty years ago. That coincides with the completion of Henry
Flagler's railroad across the Keys, and also with the redirection of water flow from the
Everglades by developers and government officials. The railroad stopped Florida Bay from
flowing into the Atlantic Ocean, while water from the Everglades was redirected towards
Florida's East Coast instead of into Florida Bay.

• Alteration of coastal habitats for urban development: mangrove deforestation and
dredging, draining, or filling in coastal wetlands all affect water quality.
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