In this video, we are going to go over intertidal zonation on the rocky shore.
On the seashore, there is an area that is exposed and above the sea level at low tide
and underwater when it is high tide, this area is called the intertidal zone.
The intertidal zone varies greatly depending on the habitat, the intertidal region on a
sandy beach or in a mangrove swamp or on a rocky shore greatly differ.
The rocky shore because it has a solid surface for organisms to attach to, in addition to
the varying physical and biological stresses in this area, creates horizontal zonation
of species.
The rocky intertidal can be divided into four general zones; the spray zone, the upper intertidal
zone, the mid intertidal zone, and the lower intertidal zone.
Just below the lower intertidal zone is the sub-tidal zone.
Often in the intertidal an organism's upper limit is determined by the physical stresses
such as the organism's ability to cope with desiccation or temperature fluctuations.
Whereas an organism's lower limit on the rocky shore is more determined by the biological
factors such as predation and competition.
The spray zone, also known as the supra-littoral zone is the highest zone where marine organisms
are found on the rocky shore.
This zone is mostly dry and only kept wet by waves splashing water up into this area.
Organisms in this area are sparse.
Organisms in the spray zone are mostly exposed to physical stresses such as air exposure
and desiccation, they do not have as much biological stresses such as competition for
space as not as many species are able to inhabit this zone.
Because of these physical stresses, organisms that are found in this zone often have a protective
covering to prevent desiccation.
Organisms that inhabit this area include barnacles, limpets, and periwinkles, which all have hard
protective The next zone down the rocky shore is the upper intertidal zone.
This is the zone that is only covered by water during high tides.
Organisms in this zone are subject to high levels of both biological and physical stresses.
This zone is a more diverse zone than the spray zone, and in turn, there is more competition
and predation between species.
Organisms in this zone are also subject to potential desiccation, exposure to air when
it is not high tide as well as the effects of this zone getting buffeted by waves as
the tides goes in and out over the day.
This zone is dominated by barnacles, they are well adapted to the physical elements
of this zone and well protected from predators such as shore crabs and shorebirds by their
protective casing.
Other organisms found in this zone include periwinkles.
limpets, chitons, shore crabs, and marine snails.
In addition, algae can be found in this zone, but it is usually limited to green algae as
it can better handle long exposure to sunlight.
The next zone down the rocky shore is the middle intertidal zone.
This is the zone that is regularly covered by water.
It is covered and uncovered twice a day by the tides.
This zone is even more diverse than the upper intertidal zone as it has more time submerged
and less time exposed to the elements.
Biological stresses are more of a factor here, the more diverse the species and abundance
of those species means more competition for space and food, as well as more species that
can predate on others.
Physical elements such as desiccation and air exposure are still factors when it is
low tide, but not as much due to the reduced time this zone is not covered by the tide.
Organisms in this zone are still exposed to wave action though, so adaptations for strong
attachment is still found in species in this zone.
Organisms that inhabit this area include; barnacles, sponges, algae, mussels, sea stars,
sea anemones, shore crabs, and gastropods.
Within the middle intertidal due to the pressure of competition and predation on the species
found in this zone, you start to see some of the lower limits of species on the shore.
A key example is seen in barnacles, they are mostly found at the higher parts of this zone,
the lower limit is determined usually by the presence of mussels.
Mussels are more prone to desiccation than barnacles and cannot as easily inhabit the
higher levels of this zone.
Simultaneously the barnacles have less competition for space being higher up the shore.
Where mussels attach themselves they end up suffocating the barnacles underneath, limiting
the barnacle's ability to be in the same area.
The next and lowest zone of the rocky shore is the lower intertidal zone.
This is the zone that is usually submerged and is only exposed at very low tides.
This zone is even more diverse, now able to host an array of algaes and marine organisms
such as small fish.
The main stresses in this zone come from biological stresses due to the greater diversity of species
in this zone, such as competition and predation.
There are not as many physical stresses in this zone as there is very little exposure
to the air, heat, and wave action that occur at higher levels up the shore.
A key feature of this zone is the presence of brown algae, other organisms present include
encrusting sponges, shore crabs,, sea urchins, gastropods, sea cucumbers, abalone, and small
fish.
Just under the intertidal zone is the sub-tidal zone.
This zone is very rarely exposed and is mentioned because many predator species live in this
zone such as octopus and larger fish that predate on organisms living in the low intertidal
zone.
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