Intertidal Zone
Adaptations to a harsh life
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
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
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.
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
Typical Rocky Shore
Soft Bottom Shore
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
Examples of Intertidal Animals
A periwinkle is A sea urchin is found in
commonly found in areas that remain wet 99
percent of the time –
the higher zones of
either in the low zones or
the intertidal area in tide pools
It can survive days It would die if exposed
without being to air for any extended
submerged period of time
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
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
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
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
Light color reflects light
Ridges allow heat to escape
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
Picture of a crab burrowing into
A rock crevice
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
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
Mussel with
Byssal thread
Attached to
glass
Wave Shock
Shell shape also helps an animal survive
wave shock
Shellsof 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
Asrocks 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