Intertidal Zone

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Intertidal Zone

• Adaptations to a harsh life

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Definition of Intertidal

• Also known as the littoral zone
• The area between the high water mark and the low
  water mark
• Where the land meets the ocean
• Sometimes dry sometimes wet

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• The intertidal zone is rich with nutrients that
  are replenished with each tide
• Each wave that enter the zone carries with it
  more plankton that the organisms that live in
  this area survive on
• Dead animals and plants also enter this area
  feeding scavengers like hermit crabs and shore
  crabs
• Constantly redesigned by three forces wind,
  water and rock
• Winds move across the rock eroding it as each
  wave carries more sediment away

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High and Low Tide
Remember that tides are caused by the gravity of
the sun and The moon. Approximately twice a day
the ocean swells as water Is pulled away from the
center of the earth due to these forces. This
creates a high tide.
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Type of Shore Line

• Rocky shore
• Occur on steep coasts with very little sediment
• Occur on active margins where the land was
  recently uplifted
• Can be caused by erosion of sediment due to wave
  action
• Soft shore
• Areas where large amount of sediment has
  accumulated more later

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Typical Rocky Shore
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Soft Bottom Shore
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Water Loss

• The loss of water is also called desiccation
• Intertidal animals must avoid major desiccation
  and tolerate minor desiccation
• This is a problem because these animals only have
  gills to breathe and eat only other marine
  organisms
• All organisms are approximately 70 percent water
  and need to retain that water to live

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Examples of Intertidal Animals

• A periwinkle is commonly found in the higher
  zones of the intertidal area
• It can survive days without being submerged

• A sea urchin is found in areas that remain wet 99
  percent of the time either in the low zones or
  in tide pools
• It would die if exposed to air for any extended
  period of time

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Run and Hide Strategy

• Movement of animals to follow the tide
• Animals move to areas that remain wet when the
  tide goes out
• Some animals only live in those areas that remain
  wet and are shaded at all times tide pools are
  depressions that hold water when the tide goes
  out

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Clam up Strategy

• The animals that use this type of strategy have a
  protective covering like a shell that they close
  to prevent water loss
• These animals clamp themselves close to the rock
  sometimes even creating depressions and seal
  the opening
• Some animals produce a mucus that they use to
  help prevent water loss from openings they can
  not close

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Dry Out Strategy

• Some animals allow themselves to just dry out
• A chiton has the ability to loose 70 percent of
  its water and still survive

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Temperature

• Sea water remains relatively constant but air
  temperatures vary dramatically
• All animals in the littoral zone must be able to
  tolerate extreme changes including animals in
  the tide pools
• Some animals have the ability just to withstand
  this variance Others..
• move to areas that have water and are shade
• Have a lighter shell color to reflect light
• Have ridges to help get rid of excess heat

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Light color reflects light
Ridges allow heat to escape
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Salinity

• Fluctuates largely due to
• Rain dilutes the water in tide pools
• Evaporation increases the salinity because only
  pure water evaporates living the salt behind
• Animals often tolerate these changes by
• Sealing off their shells to the environment
• Burrowing into the environment
• Not tolerating it they die in extreme cases

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Picture of a crab burrowing into A rock crevice
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Feeding Restrictions

• Most of the organisms in the littoral zone are
  filter feeders or predators
• Filter feeders filter food out of the water using
  feeding appendages
• This means that they must go without food during
  low tide when there is not food to filter or when
  they have their shells closed to prevent
  desiccation
• In areas where the tide is out for long periods
  of time the animals grow more slowly due to the
  lack of food

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Coping with Wave Shock

• Animals that live in an area with wave shock are
  usually sessile and have a means of anchoring
  themselves to the rock
• Seaweed uses holdfasts
• Mussels and other shell fish uses byssal threads
  as the animal moves new threads are attached to
  the rock and the old ones are detached
• Limpets and chitons use their radula to suction
  to the rock
• Fish in this area lack a swim bladder which
  allows them to sink to the bottom

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Mussel with Byssal thread Attached to glass
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Wave Shock

• Shell shape also helps an animal survive wave
  shock
• Shells of organisms in areas where there is a lot
  of wave shock tend to be compact in shape and
  have thick shells
• In times of strong wave action like during
  storms mortality is high
• As rocks are turned over those that live on top
  are crushed and those that lived on the bottom
  often are not adapted to the exposure they face
  on top