Page 4 - The British Big Four

oral formations are divided into three
C zones. The Shallow Shore extends from
the shoreline to about 30 feet in depth. An
excellent example is Bonaire, Netherlands
Antilles where the reef can extend onto the
shoreline. Platform Reefs (that we refer to
as the Mid Reef ) extend from 30 to 50 feet
and lack the structure of the Edge Reef (The exist in waters surrounding the Equator.
Towering Deep) that can extend to 180 feet.
The age of the Mid Reef structure varies be- oceanic acidification, blast fishing, cyanide
tween 1,000 and 10,000 years. Edge reefs,
characterized by the Great Towering Reefs
of Cozumel, Mexico and the Cayman Islands
are continuous structures rising into coral
peaks high above the edge of the drop off
zone and extending to a depth of 180 feet.
Edge Reefs can be hundreds of thousands of
years old. They are magnificent structures
and safely within range of the recreational
diving.
oral reefs deliver ecosystem services to could become drowned reefs, covered by so
C tourism, fisheries and shoreline protec-
tion. The annual global economic value of
coral reefs was estimated at $375 billion in
2002. However, coral reefs are fragile eco-
systems, partly because they are very sensi-
tive to water temperature and typically only
They are under threat from climate change,
fishing for aquarium fish, overuse of reef
resources, and harmful land-use practices,
including urban and agricultural runoff and
water pollution, which can harm reefs by en-
couraging excess algal growth.
M ost coral reefs were formed after the
last glacial period when melting ice
caused the sea level to rise and flood the
continental shelves. This means that most
coral reefs are less than 10,000 years old.
As communities established themselves on
the shelves, the reefs grew upwards, pacing
rising sea levels. Reefs that rose too slowly
much water that there was insufficient light.
Coral reefs can also be found in the deep sea
away from continental shelves, around oce-
anic islands and as atolls. The vast majority
of these islands are volcanic in origin. The
few exceptions have tectonic origins where
plate movements have lifted the deep ocean
floor on the surface. Healthy tropical coral
reefs grow horizontally from 1 to 3 centim-
eters per year, and grow vertically anywhere
from 1 to 25 centimeters per year; however,
they grow only at depths shallower than 150
meters because of their need for sunlight,
and cannot grow above sea level. Live coral
are small animals embedded in calcium car-
bonate shells. It is a mistake to think of coral
as plants or rocks. Coral heads consist of
accumulations of individual animals called
polyps, arranged in diverse shapes. Polyps
are usually tiny, but they can range in size
from a pinhead to 30 centimeters across.