280 CHAPTER 11 The Ocean and Fisheries0
0 2000 kilometers1000 2000 miles60 °S30 °S0 °30 °N60 °N60 °S30 °S0 °30 °N60 °NTim Laman/NG Image CollectionAdapted from Marangos, J. E., M. P. Crosby, and J. W. McManus. “Coral reefs and biodiversity: a critical and threatened relationship.”
Oceanography, Vol.9 (1996).b. A coral reef in Fiji has a variety of soft corals as well as several
fish species.
a. This map shows the distribution of coral reefs around the
world. There are more than 6000 of them worldwide.for zooxanthellae (symbiotic algae) that live and pho-
tosynthesize in their tissues. In addition to obtaining
food from the zooxanthellae that live inside them, coral
animals capture food at night with stinging tentacles
that paralyze plankton (small or microscopic organisms
carried by currents and waves) and small animals that
drift nearby. The waters where coral reefs grow are of-
ten poor in nutrients, but other factors are favorable for
high productivity, including the presence of zooxanthel-
lae, appropriate temperatures, and year-round sunlight.
Coral reef ecosystems are the most diverse of all ma-
rine environments (Figure 11.6b). They contain hun-
dreds of species of fishes and invertebrates, such as giant
clams, snails, sea urchins, sea stars, sponges, flatworms,
brittle stars, sea fans, shrimp, and spiny lobsters. Austra-
lia’s Great Barrier Reef occupies only 0.1 percent of the
ocean’s surface, but 8 percent of the world’s fish species
live there. The multitude of relationships and interac-
tions that occur at coral reefs is comparable only to those
of the tropical rain forest. As in the rain forest, competi-
tion is intense, particularly for light and space to grow.bottom-dwelling animals, such as worms and clams, burrow.
Bacteria are common in marine sediments, found even at
depths more than 500 m (1625 ft) below the ocean floor.
The deeper parts of the benthic environment are divided
into three zones, from shallowest to deepest: the bathyal,
abyssal, and hadal zones. The communities in the rela-
tively shallow benthic zone that are particularly produc-
tive include coral reefs, sea grass beds, and kelp forests.
Corals are small, soft-bodied animals similar to jellyfish
and sea anemones. Corals live in hard cups, or shells, of
limestone (calcium carbonate) that they produce using
the minerals dissolved in ocean water. When the coral
animals die, the tiny cups remain, and a new generation
of coral animals grows on top of these. Over thousands
of generations, a coral reef forms from the accumulated
layers of limestone. Most coral reefs consist of colonies of
millions of individual corals.
Coral reefs are found in warm (usually greater than
21°C [70°F]), shallow seawater (Figure 11.6a). The liv-
ing portions of coral reefs grow in shallow waters where
light penetrates. The tiny coral animals require light
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