Climate and Biodiversity - Environmental Science - page 100

this reason, estuaries and their associated coastal wet-
lands are some of the earth's most productive ecosys-
tems and provide other important ecological and eco-
nomic services.
These systems filter out toxic pollutants, excess
plant nutrients, sediments, and other pollutants. They
reduce storm damage by absorbing the energy of
waves and storing excess water produced by storms.
They also provide food, habitats, and nursery sites for
numerous aquatic species. Bad news: We are degrading
or destroying some of the ecological services that these
important ecosystems provide at no cost.

of the sea. Such real estate is so scarce and valuable that
coastal developers frequently remove the protective
dunes or build behind the first set of dunes and cover
them with buildings and roads. Large storms can then
flood and even sweep away seaside buildings and se-
verely erode the sandy beaches. Some people inac-
curately call these human-influenced events “natural
disasters.”

Case Study: Coral Reefs
Coral reefs are biologically diverse and productive
ecosystems that are increasingly stressed by human
activities.
Coral reefs form in clear, warm coastal waters of the
tropics and subtropics (Figure 5-23). These stunningly
beautiful natural wonders are among the world's old-
est, most diverse, and productive ecosystems, and they
provide homes for one-fourth of all marine species
(Figure 5-31, p. 102).
Coral reefs are formed by massive colonies of tiny
animals called polyps (close relatives of jellyfish). They
slowly build reefs by secreting a protective crust of
limestone (calcium carbonate) around their soft bod-
ies. When the polyps die, their empty crusts remain
behind as a platform for more reef growth. The result-
ing elaborate network of crevices, ledges, and holes
serves as calcium carbonate “condominiums” for a va-
riety of marine animals.
Coral reefs represent a mutually beneficial rela-
tionship between the polyps and the single-celled al-
gae called zooxanthellae (“zoh-ZAN-thel-ee”) that live
in the tissues of the polyps. The algae provide the
polyps with color, food, and oxygen through photo-
synthesis. The polyps, in turn, provide the algae with a
well-protected home and some of their nutrients.
Although coral reefs occupy only about 0.1%
of the world's ocean area, they provide numerous
free ecological and economic services. They help
moderate atmospheric temperatures by removing
CO 2 from the atmosphere, act as natural barriers that
help protect 15% of the world's coastlines from ero-
sion by battering waves and storms, and support at
least one-fourth of all identified marine species and
almost two-thirds of marine fish species. Economi-
cally, they produce about one-tenth of the global fish
catch and one-fourth of the catch in developing coun-
tries, and provide jobs and building materials for
some of the world's poorest countries. They also sup-
port fishing and tourism industries worth billions of
dollars each year.
Coral reefs are vulnerable to damage because they
grow slowly and are disrupted easily. They also thrive
only in clear and fairly shallow water of constant high
salinity. This water must have a temperature of
18-30°C (64-86°F).

Rocky and Sandy Shores: Living
with the Tides
Organisms in coastal areas experiencing daily low and
high tides have evolved many ways to survive under
harsh and changing conditions.
The area of shoreline that appears between low and
high tides is called the intertidal zone. Organisms liv-
ing in this zone must be able to avoid being swept
away or crushed by waves, and evade or cope with be-
ing immersed during high tides and left high and dry
(and much hotter) at low tides. They must also survive
changing levels of salinity when heavy rains dilute salt
water. To deal with these stresses, most intertidal or-
ganisms hold on to something, dig in, or hide in pro-
tective shells.
On some coasts, steep rocky shores are pounded by
waves. The numerous pools and other niches in the
rocks in their intertidal zones contain a great variety of
species that occupy different niches (Figure 5-29, top).
Other coasts have gently sloping barrier beaches, or
sandy shores, with niches for different marine organ-
isms (Figure 5-29, bottom). Most of them keep hidden
from view and survive by burrowing, digging, and
tunneling in the sand. These sandy beaches and their
adjoining coastal wetlands are also home to numerous
birds that occupy specialized niches by feeding on dif-
ferent types of crustaceans, insects, and other organ-
isms (Figure 4-5, p. 69).
Barrier islands are low and narrow sandy islands
that form offshore from a coastline. These beautiful but
very limited pieces of real estate are prime targets for
real estate development. Living on these islands can be
risky. Sooner or later many of the structures humans
build on low-lying barrier islands, such as Atlantic
City, New Jersey, and Miami Beach, Florida, are dam-
aged or destroyed by flooding, severe beach erosion,
or major storms (including hurricanes; see Figure 3 in
Science Supplement 6 at the end of this topic).
Undisturbed barrier beaches have one or more
rows of natural sand dunes in which the sand is held in
place by the roots of grasses (Figure 5-30, p. 102). These
dunes serve the first line of defense against the ravages