146 CHAPTER 6 Ecosystems and Evolution
Global
Locator© William A. Bake/CORBIS © Photoshot/Alamy
NG Mapsb. A mangrove forest in Risong Bay, Palau, Micronesia, with an
underwater view of the prop root system. Mangrove roots grow into
deeper water as well as into mudflats that are exposed at low tide.
Many animals live among the mangroves’ complex root system.a. A salt marsh along Okracoke Harbor, Outer Banks,
North Carolina.
high level of light that penetrates the shallow water, and
the many plants that form the base of a detritus food web.
Temperate estuaries usually feature salt marshes,
shallow wetlands in which salt-tolerant grasses grow
( Figure 6.15a). Salt marshes perform many ecosystem
services, including providing biological habitats, trap-
ping sediment and pollution, supplying groundwater,
and buffering storms by absorbing their energy, which
prevents flood damage elsewhere.
Mangrove forests, the tropical equivalent of salt
marshes, cover perhaps 70 percent of tropical coastlines
(Figure 6.15b). Like salt marshes, mangrove forests
provide valuable ecosystem services. Their interlacing
roots are breeding grounds and nurseries for several
commercially important fishes and shellfish, such as
mullet, spotted sea trout, crabs, and shrimp. Mangrove
branches are nesting sites for many species of birds,
such as pelicans, herons, egrets, and roseate spoonbills.
Mangrove roots stabilize the submerged soil, thereby
preventing coastal erosion and providing a barrier
against the ocean during storms.Brackish Ecosystems: Estuaries
Where the ocean meets the land,
there may be one of several kinds
of ecosystems: a rocky shore, a
sandy beach, an intertidal mud
flat, or a tidal estuary. Water lev-
els in an estuary rise and fall with
the tides; salinity fluctuates with
tidal cycles, the time of year, and
precipitation. Salinity also changes gradually within the
estuary, from fresh water at the river entrance, to brackish
(somewhat salty) water, to salty ocean water at the mouth
of the estuary. Because estuaries undergo significant
daily, seasonal, and annual variations in physical factors
such as temperature, salinity, and depth of light penetra-
tion, estuarine organisms must have a high tolerance for
changing conditions.
Estuaries are among the most productive ecosystems
in the world. Their high productivity is brought about
by nutrient transport from land, tidal action that rapidly
circulates nutrients and helps remove waste products, a
estuary A coastal
body of water, partly
surrounded by land,
with access to the
open ocean and a
large supply of fresh
water from a river.ÃÌÕ>ÀiÃÊUÊ}ÕÀiÊÈ°£xÊ