ADAPTATIONS OF ROCKY SHORE ORGANISMS TO THEIR WAY OF LIFE
*This EXEMPLAR only considers 2 organisms - in the actual internal you need to do 3!
Title: Rocky shore organisms adaptations for obtaining nutrition
Organism 1: Half crab (Petrolisthes elongatus)
Half crabs are scavengers. This means that they feed on dead plant
and animal material in their habitat (Wikipedia, 2017). On the rocky
shore they are found commonly in the intertidal zone under rocks,
coming out to feed when the tide is in.
Organism 2: Neptune’s necklace (Hormosira banksii)
Adaptation 1: A structural adaptation that the half crab has for
obtaining nutrition is a third leg which has silky threads on the end.
This acts like a strainer to catch debris including plant and animal
material that drift past the crab with the tide. It then passes this food to
its mouth by using a left-right sweeping motion (MERC, 2012). Key
aspects of this adaptation are the long silky threads, and that they are
located on the end of the third leg. This is so that they act like a
strainer to capture food particles that can then be brought to the mouth
due to the length of the leg..
Adaptation 1: A physiological adaptation that Neptune’s necklace has is
that it contains not just chlorophyll a (the normal pigment found in
greenn plants) but a brown pigment also. The key aspects of this are
that this pigment has a high concentration of fucoxanthan and that it
helps the seaweed absorb light at different wavelengths to chlorophyll a
(Basic Biology, 2017).
This adaptation helps the half crab survive on the rocky shore habitat
because it helps the crab catch plant and animal material in an
environment where the tide coming in and out washes it around. The
silky threads are able to be held out to capture any of this food that
comes past the half crab efficiently enough to enable it to get enough
food to provide energy to carry out its other life processes. Without
this adaptation the half crab would not be able to catch enough food.
Diagram showing silky threads on third leg (left side):
Neptune’s necklace is a brown seaweed and a producer. This means it
makes it’s own food through carrying out photosynthesis (Wikipedia,
2017). This seaweed is found commonly in the low tide zone on the
rocky shore where water is abundant due to the tide coming in.
This adaptation helps the seaweed survive as it can find space to
establish away from other seaweed of different colours to absorb more
light energy for carrying out photosynthesis. This ensures the seaweed
is able to reduce competition for light to produce sufficient glucose from
carbon dioxide.
This is used as the energy needed to carry out the other life processes,
eg. through cellular respiration which releases energy from food, to
survive on the rocky shore.
Diagram showing structure of the fucoxanthin compound in the brown
pigment in this seaweed:
Adaptation 2: A behavioural adaptation the half crab has is that it uses
its large claws to dig in the debris on the seafloor to stir up plant and
animal material that then is caught in the adaptation above (MERC,
2012). Key aspects of this adaptation are the long shape of the claws
and therefore the large surface area available for scraping along the
seafloor.
This helps the half crab survive on the rocky shore as the large claws
are able to disturb sufficient seafloor to effectively disturb enough plant
and animal debris for feeding on. It works well as the seafloor is
relatively soft due to the tide coming in and out.
By doing this it is able to gain sufficient energy to carry out all of its
other life processes, for example, movement to be able to gather food
and move away from predators..
Diagram showing large claws the half crab uses to dig to disturb plant
and animal material on the seafloor:
Adaptation 2: A structural adaptation of Neptune’s necklace are its
strings of olive-brown, spherical, pneumatocysts. Key aspects of these are
they they are filled with air that contains the gas carbon dioxide which is
able to enter and leave through tiny pores or holes (Wikipedia, 2017).
This helps this seaweed survive on the rocky shore as carbon dioxide is
used during photosynthesis to produce glucose. The air being trapped
within these bubble like structures means that the branches of the
seaweed are able to float to the surface of the water to capture more
light energy from the sun for carrying out photosynthesis. This is
important as seaweed does not have a trunk like structure like other
plants for support as the sea provides more support than air.
The glucose is used as a source of energy for carrying out other life
processes to help the seaweed survive in its rocky shore habitat
(Pathwayz, 2017).
Diagram showing the bubble like pneumatocysts:
Comparison, including advantages and limitations of the adaptations for obtaining nutrition:
Both the half crab and Neptune’s necklace seaweed are similar in that they have to obtain nutrition in a challenging environment where the tide
going in and out means they have to be adapted to survive. Obtaining nutrition is important as …
In comparison to Neptune’s necklace the half crab adaptation of ... is limited by … , however it has an advantage as …
In comparison to the half crab the Neptune’s necklace adaptation of … is limited by …., however it has an advantage as ...
The main idea however is that they are different as they feed in different ways. The half crab is a scavenger so it has to … whereas the
Neptune’s necklace is a producer so it has to …
More specifically the two structural adaptations they have are both long and tough to withstand the extreme conditions they live in. Their being
long means that .... Their being tough means that ...
What is different is the physiological adaptation of the seaweed in comparison to the behavioural adaptation of the half crab. This is because half
crabs are able to move so that they can … As the seaweed is unable to move it means that instead it must ….
In summary, the similarities and differences in the adaptations of these two types of feeder are due to … and this is because ….
Important note: For excellence this section must clearly link ideas to the organism and its way of life in terms of how it obtains
nutrition.
For example:
Adaptation --- Habitat --- Nutrition
Adaptation --- Activity --- Nutrition