Page 450 - Environment: The Science Behind the Stories

WeIGhING the ISSUeS

COaStaL deveLOpMeNt A developer wants to build a large
marina on an estuary in your coastal town. The marina would
boost the town’s economy but eliminate its salt marshes.
What consequences would you expect for property values?
For water quality? For wildlife? As a homeowner living adja-
cent to the marshes, how would you respond? Do you think
that developers or town officials should offer homeowners
insurance against damage from storm surges when a protec-
tive salt marsh is destroyed?

the sunlit surface. Some kelp reaches 60 m (200 ft) in height (a) Coral reef community
and can grow 45 cm (18 in.) per day. Dense stands of kelp
form underwater “forests” (Figure 16.13). Kelp forests supply
shelter and food for invertebrates and fish, which in turn pro-
vide food for predators such as seals and sharks (indeed, kelp
forests were the setting for our discussion of keystone spe-
cies in Chapter 4). Kelp forests also absorb wave energy and
protect shorelines from erosion. People in Asian cultures eat
some types of kelp, and kelp provides compounds known as
alginates, which serve as thickeners in such consumer prod-
ucts as cosmetics, paints, paper, soaps, and ice cream.

Coral reefs are treasure troves
of biodiversity
Shallow subtropical and tropical waters are home to coral
reefs. A reef is an underwater outcrop of rock, sand, or other (b) Bleached coral
material. A coral reef is a mass of calcium carbonate com-
posed of the skeletons of tiny marine animals known as corals. Figure 16.14 Coral reefs provide food and shelter for a tre-
A coral reef may occur as an extension of a shoreline, along mendous diversity (a) of fish and other creatures. Today these
reefs face multiple stresses from human impacts. Many corals have
a barrier island paralleling a shoreline, or as an atoll, a ring died as a result of coral bleaching (b), in which corals lose their zoox-
around a submerged island. anthellae. Bleaching is evident in the whitened portion of this coral.
Corals are tiny invertebrate animals related to sea anemo-
nes and jellyfish. They remain attached to rock or existing reef zooxanthellae.) As corals die, their skeletons remain part
and capture passing food with stinging tentacles (see photo of the reef while new corals grow atop them, increasing the
on p. 446). Corals also derive nourishment from symbiotic reef’s size.
algae known as zooxanthellae, which inhabit their bodies and Like kelp forests, coral reefs protect shorelines by
produce food through photosynthesis. Most corals are colo- absorbing wave energy. They also host tremendous biodi-
nial, and the colorful surface of a coral reef consists of mil- versity (Figure 16.14a). This is because coral reefs provide
lions of densely packed individuals. (The colors come from
complex physical structure (and thus many habitats) in shal-
low nearshore waters, which are regions of high primary CHAPTER 16 • M AR in E A nd Co A s TA l s ys TEM s A nd R E sou R CE s
Figure 16.13 “Forests” of tall brown algae known as kelp productivity. Besides the staggering diversity of anemones,
grow from the floor of the continental shelf. Numerous fish sponges, hydroids, tubeworms, and other sessile (stationary)
and other creatures eat kelp or find refuge among its fronds. invertebrates, innumerable molluscs, flatworms, sea stars, and
urchins patrol reefs, while thousands of fish species find food
and shelter in reef nooks and crannies.
Coral reefs are experiencing alarming declines world-
wide, however. Many have undergone “coral bleaching,”
a process that occurs when zooxanthellae die or leave the
coral, depriving it of nutrition. Corals lacking zooxanthellae
lose color and frequently die, leaving behind ghostly white
patches in the reef (Figure 16.14b). Coral bleaching is thought
to result from increased sea surface temperatures associated
with global climate change, from the influx of pollutants,
from unknown natural causes, or from combinations of these
factors. 449

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