Chapter 11 The Dynamic Shoreline

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

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Salt marshes are intertidal flats covered by
grassy vegetation.
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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.

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

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A coral reef is an organically constructed,
wave-resistant, rock-like structure created by
carbonate-secreting organisms.
Coral Reefs
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• 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.
• 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 benthic filter
  feeders in nutrient-rich water where
  phytoplankton are abundant.

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Coral Reef Classifications
Fringing Reefs cling to the margin of
land. Barrier Reefs are separated from land by
a lagoon. Atolls are ring-shaped islands of
coral reef enclosing lagoons.
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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.
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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.

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

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Coastlines are desirable areas for human
habitation, but human activity conflicts with the
dynamic state of coastal systems.
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Impact of People on the Coastline

• Humans try to stabilize the coastline in two
  ways by interfering with longshore sand
  transport, and by redirecting wave energy to
  prevent erosion.
• Preventing of sand drift involves jetties and
  groins.
• Redirecting wave energy involves breakwaters and
  seawalls.
• Beach nourishment with sand is expensive and
  temporary.
• An increase in sea level from global warming will
  cause more land to be flooded and threaten more
  coastal buildings.

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A map showing shore erosion by region. One
example of shore erosion is the lighthouse on
Cape Hatteras, which was moved during 1998 and
1999 to protect it from destruction. It was
threatened by rising sea levels and a changing
shoreline.
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