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Phenomenon of Zonation

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Tides are caused by rising and falling of ocean surfaces owing to the moon’s tidal force. This tides results in changes in the water level. The intertidal zone is exposed at low tide and submerged at high tide. The spray zone which is never submerged, receives ocean water due to the crashing waves. The high tide zones are only submerged briefly when there is a highest tide. The middle is regularly exposed and submerged by the tide. The low tide zone is regularly submerged and it is exposed to the air during the lowest tides. The distribution of diverse rocky intertidal organisms is usually dictated by zonation because they are the only organism that that are adapted to live in each zone. The organisms that are involved include Crustaceans, mollusks and enchinoderms. It is important to appreciate the major environmental gradient and interactions that provides a framework for organizing the complex array of shores types. The physico-chemical limiting factors and dynamic complex biological process shapes the ecology on the shore and they vary in terms of intensity as well as gradients.

The zonation patterns on rocky shores have long been studied as earlier as 1882, 1891, 1909,1915 and 1933 by Audouin and Milne-Edwards, Baker, Walton and Colman respectively. The main biological features of rocky shores were recorded with a sketch book or camera and they adopted a broad-brush qualitative approach and revealed consistent pattern worldwide.  

Causes of zonation on sheltered rocky shores

The intertidal areas are at the interface between marine and the terrestrial habitats and they are inhabited by marine organism such as shorebirds and passerines that usually feed on the intertidal animals. Invertebrates living in these intertidal zones face environmental conditions variations in the marine habitat. The action of marine tides exposes intertidal invertebrates to the air at regular intervals. The tolerance of the animals to exposure to the air as well as higher temperatures forms a major determinant of the zonation patterns among the species that form intertidal communities.

The upper intertidal is inhabited by only the species that are resistant to water loss, heat stress, mechanical stress from wave action as well as osmotic stress that is caused by rainfall during the low tide. Many intertidal invertebrates have planktonic larvae and therefore the processes that play major role in determining the species composition of intertidal communities. The species that are found on one locality forms a subset of the pool of the species whose larvae occur in the coastal currents.

Density and diversity of plants and invertebrates happen to reach the high level on rocky shores because they are usually bathed in nutrients and plankton-rich waters which provide a good substrate for the growth of the growth of algal. This result in vertical zonation of the major organisms and forms a well defined horizontal band of populated by few species of adapted to this intertidal zone.

The coastal factors such as slope as well as air exposure time are crucial in determining these zonation patterns. Biological processes work to structure these rocky shore communities. Interference completion for attachment space on the rocky substrate is intense among the species of algae as well as that of between sessile filter-feeding invertebrates like mussels and barnacles. Predation by organism like crabs, starfish and gastropods is an important factor in the structuring on the more sheltered shores. Their action and preference for certain prey inhibit one prey from out-competing others and affects the distribution and relative abundances of the prey species.

The effects of grazers such as limpets and littorinid snails on algae can be experienced. The interactions of physical factors competition and predation together with spatial and temporal variability in larval recruitment are the main determinants of community structure and species composition in the rocky shores system.


The aim of the experiment was to learn about the influence of major environmental and biological processes on the pattern of distribution of rocky shores communities as well as learn how classical and recent experiments have been done in order to understand the causes of these patter to look for evidence that environmental gradients and/or inter-specific competition influence species zonation. Lastly, it will enable one to gain experience in the scientific processes of formulating a hypothesis, testing it empirically and writing up the findings in a scientific report. These objectives will be useful in realizing the hypothesis which proposes that productivity increases from high to low shore because conditions become more benign. Algal competitive ability increases from high to low on the shore. Tall plants are assumed to be stronger competitors than short plants and that environmental conditions are harsher on the high than the low shore, reducing diversity of species and finally, the numbers of species of seaweeds and animals increase down the shore

Research gap

Rock quality designation is considered in the process of designing the of the underground and open spaces evaluation of leaching potential of metallic ore among other similar cases. This designing is affected by the number as well as geometry of the discontinuity in the rock masses

The horizontal banding of the intertidal zone is caused by dominance of different organisms basically at different heights on the shore. The organisms involved are encrusting lichens and sedimentary animals such as barnacles and mussels. The ecological irrelevance of many of the experiments has led to the conclusion that the causes of zonal discontinuities has been fruitless mainly because ecological zonation is largely dependent on the competitive relations of species and therefore physiological tolerance limits play no part in this explanation. This has caused a revival of interests in the problem as well as a greater concern for the ecological realism of experiments treatments. This experiment is therefore set to bridge this gap that has remained unexplained for a long time (Dring)


Ascophyllum is the dominant species in this zone and so can only live lower down the shore. It also contains a number of turf species (filamentous red algae) and it is found between Fucusvesiculosus and fucusserratus. It merges with the two and so, Fucusvesiculosus and serratusare also found in this zone. It is shown in figure 6 that the dominant species is Fucusspiralis butspecies such as Ascophyllumnondosom and Pelvetiacanaliculata are also found in the zone. In the Pelvetia zone, Pelvetiacanaliculata dominates the zone, and unlike the other zones, there are very few other species of algae living there as conditions are the harshest.


Ascophyllum is the dominant species in this zone and so can only live lower down the shore and contains a number of turf species. Both physical and biological factors are very crucial in generating as well as maintaining the zonation pattern. The zonation is physically influenced greatly by heat, light, wind, nature water as well as temperature.

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