Tides and the action of the waves dominate the environment of the ocean rock platform and produce an area of extremes, which is one of the most diverse and challenging on earth. The ability of each species to withstand the physical factors of their environment and to compete with other organisms for the resources available governs not only how successful the species will be but also where on the rock platform it is found. Wave action not only acts as a force which tries to dislodge organisms from the rock surface but also pushes water higher up the rock face to areas not covered by the tides. Waves can cause spray which moistens the upper reaches of the platform and leaving salt deposits after prolonged dry periods.
Abiotic variables such as wind, air temperature, sun exposure, humidity, wave splash and spray are other contributing factors.
The physical, chemical and biological factors of the environment found on the ocean rock platform, cause different species to be found in various areas of the rocky surface. Many biologists refer to this variation of species distribution, as a ‘zonation pattern’. The pattern, to which they refer, consists of bands or ‘zones’ of different organisms, which seem to inhabit the rock platform at various levels. Zones are often associated with a particular species or group of species, which are called ‘indicator organisms’. While these indicator organisms may not always be present, they are often the easiest way to determine the zone with which you are dealing.
Adaptations to resist desiccation are some of the most important since it is the ability to resist drying out which determines how high on the rock platform the organism can exist. Some adaptations developed by organisms to overcome this problem include:
A.Hard external coverings – which trap water next to the body of the organism, e.g. the shells of molluscs, the exoskeletal plates of the barnacles and the calcareous tube of the Galeolaria.
B. An Operculum – helps retain water already trapped in the shell, e.g. Galeolaria, Periwinkles such as Melarphe and Melanerita, as well as Nodilittorina, Australocochelea, Morula and Bembicium.
C. Clumping together – traps water between the shells of the individuals in the group, e.g. Melarphe, Nodilittorina and Melanerita.
D. Shelter – shade e.g. Melaraphe, Modilittorina and Melanerita. Algal masses e.g. Australocochelea, Morula, Bembicium,crabs and many other species. Gutters and rock pools, e.g. Australocochelea, Morula, Bembicium,
crabs, sea urchins, sea anemones and many other species.
To overcome the problem of being swept away by the pounding waves organisms have developed several adaptations. Those with less successful adaptations are restricted to less exposed areas of the rock platform. Adaptations include:
A. Holdfasts – e.g. Durvillea, Ecklornia, Ulva, Corallina, Pterocladia, Hormosira and Phyllospora.
B. Passive resistance – e.g. Durvillea, Ecklornia, Ulva, Corallina, Pterocladia, Hormosira and Phyllospora.
C. Cementing exoskeleton to rock surface – e.g. Barnacles, oysters & Galeolaria.
D. The byssus, a series of strong threads – e.g. Mussels such as Brachidontes.
E. Basal disc – e.g. sea anemone.
F. Muscular feet e.g. chitins, limpets and periwinkles.
G. Tube feet – e.g. star fish and sea urchins.
H. Streamline shape e.g. Mussels, barnacles and limpets.
I. Use of spines for anchorage – e.g. sea urchins, which often can be found wedged in crevices or depressions made by themselves.
J. Shelter – Algal masses e.g. Periwinkles. Gutters and rock pools e.g. Periwinkles and crab