major drainage basins that represent a time series of shifts
in the major channel of the river. The youngest basins support mostly freshwater marshes because of their shallow
depth and the large volume of freshwater inflow. The older
basins support a variety of wetland types including extensive salt marshes and forested wetlands. West of the Mississippi, coastal wetlands tend to occur along protected
shores behind barrier islands and along protected bays,
in once flooded ancient river valleys.
Along the Pacific coast of North America, coastal wetlands are sparse because of the rugged terrain. Small isolated wetlands along river valleys are dominated by
Spartina foliosa (a species that also exhibits short and tall
forms) accompanied by various succulents. Farther north,
the San Francisco Bay area supports wetlands dominated
by S. foliosa in the low marsh and S. virginica, Jaumea
carnosa, Triglochin maritima, and D. spicata in the high
marsh. In the Pacific Northwest, low marshes are dominated by halophytic succulents such as Salicornia
virginica, Jaumea carnosa, and Triglochin maritima as
well as several grasses and sedges such as Distichlis
spicata and Carex lyngbyei. Tufted hair grass
(Deschampsia cespitosa) commonly dominates in high
marshes, accompanied by mixes of many other species.
Central America and Caribbean
In the Caribbean islands, mangroves predominate as
fringe vegetation along the coast, in protected bays and
lagoons, and as overwash islands that are often completely
flooded by each tidal cycle. In Central America, more
extensive mangals develop, and herbaceous marshes can
be found as small isolated pockets or as narrow fringes
in front of mangrove formations.
South America
As in North America, only small isolated wetlands can be
found along the Pacific coast because of the rugged terrain
associated with the Andean chain. Extensive wetlands
occur on the Atlantic coast. Mangroves can be found
throughout the northern part of the continent, with 90 %
of the coverage by approximately 10 South American species found in Brazil, Colombia, Venezuela, Ecuador, and
Suriname (FAO, 2007). Typical salt marshes occur farther
south and are dominated by S. alterniflora in the low
marsh and S. densiflora in the high marsh along with associates such as Limonium brasiliense, Juncus acutus, and
Distichlis spicata. As one approaches Tierra del Fuego,
the region becomes arid and cold and vegetation everywhere becomes scant.
Europe
Northern European marshes are characterized by a pioneer
zone thinly vegetated with Spartina anglica and Salicornia
spp., an intermediate zone populated with a variety of halophytes such as Aster tripolium, and an upper marsh zone
where Festuca rubra, Juncus gerardii, and Elymus
athericus predominate. Recently, the latter species has been
invading the mid and low marsh areas (Pratolongo et al.,
2013). Large salt marshes exist along the Atlantic coast
and along the North, Baltic, and Walden seas. Coastal wetlands in the Mediterranean region are commonly associated
with river mouths; important deltaic wetlands include the
Camargue (Rhone) in France and the Ebro Delta (Ebro)
in Spain. In this area uncharacteristically, shrubby species
such as Sarcocornia fruticosa predominate in the low
marsh and Limonium spp. in the mid-marsh, and various
Juncus species usually populate the high marsh.
Asia
The variety of climatic and edaphic conditions, the extent
of the coastline, and the high frequency of embayments,
islands, flats, estuaries, and river deltas, particularly in
S.E. Asia, result in the highest biodiversity and the
greatest areal coverage of mangroves in the world. Over
55 species of true mangroves occur in Asia (FAO, 2007).
In East Asia, extensive coastal marshes occur along deltas
formed by major rivers such as the Yangtze and Huang
He. S. alterniflora was introduced to several areas in
China in the late 1970s and has displaced many of the
native plants, particularly in the lower marsh areas
(Lu and Zhang, 2013).
Oceania
This region, which includes Australia, Papua New
Guinea, New Zealand, and the S. Pacific islands, has a
very high mangrove biodiversity (close to 50 species)
but low areal extent of mangroves. They are found in
protected bays, estuaries, lagoons, and coral atolls in the
region. Close to 75 % of the mangrove coverage is concentrated in Australia (FAO, 2007). In Australia, Spartina
anglica can occur seaward of mangrove areas. In more
temperate areas, more conventional salt marsh zonation
occurs.
Africa
Mangroves occur throughout the continent. On the east
coast, mangroves often occur as narrow fringes except
where large deltas (e.g., in Mozambique and Tanzania)
allow the development of more extensive forests. Much
broader forests develop in the west coast, culminating in
the vast mangal associated with the Niger River delta that
extends up to 40 km inland and supports very large trees
that can reach 40 m in height. Salt marshes occur on the
Mediterranean, Red Sea, and Indian Ocean coasts often
behind mangroves. In Southern Africa, mangroves occur
as far south as Angola, and extensive salt marshes south
of there (Hughes et al., 1992).
Impacts to coastal wetlands
Human pressures currently cause the greatest impacts to
wetlands. These include outright habitat loss due to residential, industrial, and agricultural development and associated infrastructure; or habitat degradation as a result of
pollution, hydrological changes, and other impacts from
162
COASTAL WETLANDS
in the major channel of the river. The youngest basins support mostly freshwater marshes because of their shallow
depth and the large volume of freshwater inflow. The older
basins support a variety of wetland types including extensive salt marshes and forested wetlands. West of the Mississippi, coastal wetlands tend to occur along protected
shores behind barrier islands and along protected bays,
in once flooded ancient river valleys.
Along the Pacific coast of North America, coastal wetlands are sparse because of the rugged terrain. Small isolated wetlands along river valleys are dominated by
Spartina foliosa (a species that also exhibits short and tall
forms) accompanied by various succulents. Farther north,
the San Francisco Bay area supports wetlands dominated
by S. foliosa in the low marsh and S. virginica, Jaumea
carnosa, Triglochin maritima, and D. spicata in the high
marsh. In the Pacific Northwest, low marshes are dominated by halophytic succulents such as Salicornia
virginica, Jaumea carnosa, and Triglochin maritima as
well as several grasses and sedges such as Distichlis
spicata and Carex lyngbyei. Tufted hair grass
(Deschampsia cespitosa) commonly dominates in high
marshes, accompanied by mixes of many other species.
Central America and Caribbean
In the Caribbean islands, mangroves predominate as
fringe vegetation along the coast, in protected bays and
lagoons, and as overwash islands that are often completely
flooded by each tidal cycle. In Central America, more
extensive mangals develop, and herbaceous marshes can
be found as small isolated pockets or as narrow fringes
in front of mangrove formations.
South America
As in North America, only small isolated wetlands can be
found along the Pacific coast because of the rugged terrain
associated with the Andean chain. Extensive wetlands
occur on the Atlantic coast. Mangroves can be found
throughout the northern part of the continent, with 90 %
of the coverage by approximately 10 South American species found in Brazil, Colombia, Venezuela, Ecuador, and
Suriname (FAO, 2007). Typical salt marshes occur farther
south and are dominated by S. alterniflora in the low
marsh and S. densiflora in the high marsh along with associates such as Limonium brasiliense, Juncus acutus, and
Distichlis spicata. As one approaches Tierra del Fuego,
the region becomes arid and cold and vegetation everywhere becomes scant.
Europe
Northern European marshes are characterized by a pioneer
zone thinly vegetated with Spartina anglica and Salicornia
spp., an intermediate zone populated with a variety of halophytes such as Aster tripolium, and an upper marsh zone
where Festuca rubra, Juncus gerardii, and Elymus
athericus predominate. Recently, the latter species has been
invading the mid and low marsh areas (Pratolongo et al.,
2013). Large salt marshes exist along the Atlantic coast
and along the North, Baltic, and Walden seas. Coastal wetlands in the Mediterranean region are commonly associated
with river mouths; important deltaic wetlands include the
Camargue (Rhone) in France and the Ebro Delta (Ebro)
in Spain. In this area uncharacteristically, shrubby species
such as Sarcocornia fruticosa predominate in the low
marsh and Limonium spp. in the mid-marsh, and various
Juncus species usually populate the high marsh.
Asia
The variety of climatic and edaphic conditions, the extent
of the coastline, and the high frequency of embayments,
islands, flats, estuaries, and river deltas, particularly in
S.E. Asia, result in the highest biodiversity and the
greatest areal coverage of mangroves in the world. Over
55 species of true mangroves occur in Asia (FAO, 2007).
In East Asia, extensive coastal marshes occur along deltas
formed by major rivers such as the Yangtze and Huang
He. S. alterniflora was introduced to several areas in
China in the late 1970s and has displaced many of the
native plants, particularly in the lower marsh areas
(Lu and Zhang, 2013).
Oceania
This region, which includes Australia, Papua New
Guinea, New Zealand, and the S. Pacific islands, has a
very high mangrove biodiversity (close to 50 species)
but low areal extent of mangroves. They are found in
protected bays, estuaries, lagoons, and coral atolls in the
region. Close to 75 % of the mangrove coverage is concentrated in Australia (FAO, 2007). In Australia, Spartina
anglica can occur seaward of mangrove areas. In more
temperate areas, more conventional salt marsh zonation
occurs.
Africa
Mangroves occur throughout the continent. On the east
coast, mangroves often occur as narrow fringes except
where large deltas (e.g., in Mozambique and Tanzania)
allow the development of more extensive forests. Much
broader forests develop in the west coast, culminating in
the vast mangal associated with the Niger River delta that
extends up to 40 km inland and supports very large trees
that can reach 40 m in height. Salt marshes occur on the
Mediterranean, Red Sea, and Indian Ocean coasts often
behind mangroves. In Southern Africa, mangroves occur
as far south as Angola, and extensive salt marshes south
of there (Hughes et al., 1992).
Impacts to coastal wetlands
Human pressures currently cause the greatest impacts to
wetlands. These include outright habitat loss due to residential, industrial, and agricultural development and associated infrastructure; or habitat degradation as a result of
pollution, hydrological changes, and other impacts from
162
COASTAL WETLANDS