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Coastal Habitats. 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.

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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.
estuaries are semi enclosed bodies of water where fresh water from the land mixes with sea water

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Estuaries

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

Estuaries can be subdivided into three types based upon the relative importance of river inflow and tidal mixing.
  • 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.
the widely fluctuating environmental conditions in estuaries make life stressful for organisms

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Estuaries

The widely fluctuating environmental conditions in estuaries make life stressful for organisms.
  • 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.
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Lagoons

Lagoons are isolated to semi-enclosed, shallow, coastal bodies of water that receive little if any fresh water inflow.
  • 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.
salt marshes are intertidal flats covered by grassy vegetation

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Salt Marshes

Salt marshes are intertidal flats covered by grassy vegetation.
  • 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.
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Mangrove Swamps

Mangroves are large woody trees with a dense, complex root system that grows downward from the branches.
  • 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.
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Coral Reefs

A coral reef is an organically constructed, wave-resistant, rock-like structure created by carbonate-secreting organisms.
  • 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 polyp’s body weight.
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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.
coral reefs consist of several distinct parts developed in response to their exposure to waves

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Coral Reefs

Coral reefs consist of several distinct parts developed in response to their exposure to waves.
  • 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.
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Coral Reefs

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.

  • 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.