Marine Ecosystems
The Intertidal Zone
The intertidal area (also called the littoral zone)
is where the land and sea meet, between the high and
low tide zones. This complex marine ecosystem is found
along coastlines worldwide. It is rich in nutrients
and oxygen and is home to a variety of organisms.
Examples:
- sandy beaches
- rocks
- estuaries
- mangrove swamps
- coral reefs
Some of these regions are very productive. Many of
their inhabitants have adaptations that enable them
to survive periodic exposure to the air and wave action.
An Inhospitable, Changing Environment:
Much of this inhospitable environment is washed by
the tides each day, so organisms that live here are
adapted to huge daily changes in moisture, temperature,
turbulence (from the water), and salinity.
Moisture:
The littoral zone is covered with salt
water at high tides, and it is exposed to the
air at low tides; the height of the tide exposes
more or less land to this daily tide cycle. Organisms
must be adapted to both very wet and very dry conditions. |
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Water Movement:
The turbulence of the water is
another reason that this area can be very difficult
one in which to survive - the rough waves can
dislodge or carry away poorly-adapted organisms.
Many intertidal animals burrow into the sand
(like clams), live under rocks, or attach themselves
to rocks (like barnacles and mussels). |
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Temperature:
The temperature ranges from the moderate temperature
of the water to air temperatures that vary from
below freezing to scorching. |
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Salinity:
Depressions on the shores sometimes
form tide pools, areas that remain wet, although
they are not long-lasting features. The salinity
of tidepools varies from the salinity of the
sea to much less salty, when rainwater or runoff
dilutes it. Animals must adapt their systems
to these variations. Some fish, like sculpin
and blennies, live in tide pools. |
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Vertical Zones eg :Rocky Shores
The rocky intertidal habitat has a very rich diversity
of organisms especially in temperate climates. Attachment
is critical and competition for space is a prime factor.
The organisms are well adapted for withstanding tremendous
SURF-EXPOSURE. Also tolerance to DESICCATION (low tides
during the summer days), temperature changes, and salinity
changes( rainfall during low tide).
When the tide goes out, the phenomenon of ZONATION
is manifested - horizontal bands or zones of organisms.
This is true for both plants and animals. Each zone
has a particular color or texture from the organisms
inhabiting that particular zone. UNIVERSAL PATTERNS
of zonation, occurring throughout the world, have been
recognized, such that no matter where you might be
observing the exposed intertidal, the middle littoral
zone will often have a community of barnacles, mussels,
and rockweeds
The intertidal area or littoral area is divided into
vertical zones like bands. The names that are often
used to describe these zones are the spray zone, high
tide zone, middle tide zone, and low tide zone. Below
these is the sub-tide zone (marine evironment or subtidal
area) , which is always underwater.
Spray Zone: Also called the
Upper Littoral, the Supralittoral Fringe, the Splash
Zone, and the Barnacle Belt. This area is dry much
of the time, but is sprayed with salt water during
high tides. It is only flooded during storms and
extremely high tides. Organisms in this sparse
habitat include barnacles, isopods, lichens, lice,
limpets, periwinkles, and whelks. Very little vegetation
grows in this area. [More
information and common species in this zone here] |
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High Tide Zone: Also called
the Upper Mid-littoral Zone (Upper Eulittoral)
and the high intertidal zone. This area is flooded
only during high tide. Organisms in this area
include anemones, barnacles, brittle stars, chitons,
crabs, green algae, isopods, limpets, mussels,
sea stars, snails, whelks and some marine vegetation. [More info here] |
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Middle Tide Zone: Also called
the Lower Mid-littoral Zone (Lower Eulittoral)
. This turbulent area is covered and uncovered
twice a day with salt water from the tides. Organisms
in this area include anemones, barnacles, chitons,
crabs, green algae, isopods, limpets, mussels,
sea lettuce, sea palms, sea stars, snails, sponges,
and whelks. [More info here] |
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Low Tide Zone: Also called
the Lower Littoral Zone (Sublittoral Fringe).
This area is usually under water - it is only
exposed when the tide is unusually low. Organisms
in this zone are not well adapted to long periods
of dryness or to exteme temperatures. Some of
the organisms in this area are abalone, anemones,
brown seaweed, chitons, crabs, green algae, hydroids,
isopods, limpets, mussels, nudibranchs, sculpin,
sea cucumber, sea lettuce, sea palms, sea stars,
sea urchins, shrimp, snails, sponges, surf grass,
tube worms, and whelks. |
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Predators:
Animals that live in the littoral zone have a wide
variety of predators who eat them. When the tide is
in, littoral organisms are preyed upon by sea animals
(like fish). When the tide is out, they are preyed upon
by land animals, like foxes and people. Birds (like
gulls) and marine mammals (like walruses) also prey
on intertidal organisms extensively.
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Lakes, like oceans, can be described in terms of
zones. There are many parallels between the two but
unfortunately a separate vocabulary is used for each.
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