Coastal Habitats

1
Coastal Habitats
2
The term coast has a much broader meaning than
shoreline and includes many other habitats and
ecosystems associated with terrestrial and marine
processes.

• The six major coastal settings are estuary,
  lagoon, salt marsh, mangrove swamp and coral
  reef.
• Shorelines are one of the most productive
  ecosystems and because they are shallow, they
  strongly respond to the effects of waves, tides
  and weather.

3
Estuaries are semi-enclosed bodies of water where
fresh water from the land mixes with sea water.
12-1
Estuaries

• Estuaries originate as drowned river valleys,
  fjords, bar-built estuaries, and tectonic
  estuaries.
• Salinity typically grades from normal marine
  salinity at the tidal inlet to fresh water at the
  mouth of the river.

4
Estuaries can be subdivided into three types
based upon the relative importance of river
inflow and tidal mixing.
12-1
Estuaries

• Salt-wedge estuaries are dominated by the outflow
  from rivers.
• Partially-mixed estuaries are dominated by
  neither river inflow nor tidal mixing.
• In well-mixed estuaries tidal turbulence destroys
  the halocline and water stratification.
• Because river discharge and tidal flow vary,
  conditions within an estuary can also change,
  being well-mixed when river flow decreases
  relative to tidal mixing, to becoming a
  salt-wedge estuary at times of maximum river
  discharge.

5
The widely fluctuating environmental conditions
in estuaries make life stressful for organisms.
12-1
Estuaries

• Estuaries are extremely fertile because nutrients
  are brought in by rivers and recycled from the
  bottom because of the turbulence.
• Stressful conditions and abundant nutrients
  result in low species diversity, but great
  abundance of the species present.
• Despite abundance of nutrients, phytoplankton
  blooms are irregular and the base of the food
  chain is detritus washed in from adjacent salt
  marshes.
• The benthonic fauna strongly reflects the nature
  of the substrate and most fishes are juvenile
  forms living within the estuary until they mature
  and migrate to the ocean.

6
Lagoons are isolated to semi-enclosed, shallow,
coastal bodies of water that receive little if
any fresh water inflow.
12-2
Lagoons

• Lagoons can occur at any latitude and their
  salinities vary from brackish to hypersaline
  depending upon climate and local hydrology.
• Bottom sediments are usually sand or mud eroded
  which was from the shoreline or swept in through
  the tidal inlet.
• In the tropics, the water column is typically
  isothermal.
• In the subtropics, salinity generally increases
  away from the inlet and the lagoon may display
  inverse flow.

7
Salt marshes are intertidal flats covered by
grassy vegetation.
12-3
Salt Marshes

• Marshes are most commonly found in protected
  areas with a moderate tidal range, such as the
  landward side of barrier islands.
• Marshes flood daily at high tide and then drain
  through a series of channels with the ebb tide.
• They are one of the most productive environments.
• Marshes can be divided into two parts Low salt
  marshes and High salt marshes.
• Distribution and density of organisms in salt
  marshes strongly reflects availability of food,
  need for protection, and frequency of flooding.

8
Mangroves are large woody trees with a dense,
complex root system that grows downward from the
branches.
12-4
Mangrove Swamps

• Mangroves are the dominant plant of the tropical
  and subtropical intertidal area.
• Distribution of the trees is largely controlled
  by air temperature, exposure to wave and current
  attack, tidal range, substrate and sea water
  chemistry.
• Detritus from the mangrove forms the base of the
  food chain.

9
A coral reef is an organically constructed,
wave-resistant, rock-like structure created by
carbonate-secreting organisms.
12-5
Coral Reefs

• Most of the reef is composed of loose to
  well-cemented organic debris of carbonate shells
  and skeletons.
• The living part of the reef is just a thin veneer
  on the surface.
• Corals belong to the Cnidara.
• The animal is the coral polyp.
• The corallite is the exoskeleton formed by the
  polyp.
• Corals share a mutualistic relationship (mutually
  beneficial) with the algae zooxanthallae which
  lives within the skin of the polyp and can
  comprise up to 75 of the polyps body weight.

10
12-5
Coral Reefs

• Corals can be either solitary or colonial.
• Corals can not survive in fresh, brackish water
  or highly turbid water.
• Corals do best in nutrient poor water because
  they are easily out-competed by benthonic filter
  feeders in nutrient-rich water where
  phytoplankton are abundant.

11
Coral reefs consist of several distinct parts
developed in response to their exposure to waves.
12-5
Coral Reefs

• The algal ridge occurs on the windward side of
  the reef and endures the pounding waves.
• The butress zone is the reef slope extending down
  from the algal ridge.
• The reef face extends downward from the butress
  zone and usually is devoid of living colonial
  corals because insufficient light reaches this
  depth.
• The reef terrace is landward of the algal ridge
  and lies at mean water level.
• The shape of the colonial coral masses reflects
  the environment in which they live.

12
As a result of corals growing continuously upward
towards the sunlight as sea level rises and/or
land subsides and, coral reefs pass through three
stages of development.
12-5
Coral Reefs

• Fringe reefs form limestone shorelines around
  islands or along continents and are the earliest
  stage of reef development.
• As the land is progressively submerged and the
  coral grows upward, an expanding shallow lagoon
  begins to separate the fringe reef from the
  shoreline and the reef is called a barrier reef.
• In the final stage the land vanishes below the
  sea and the reef forms a ring of islands, called
  an atoll, around a shallow lagoon.