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Investigate the difference in density of limpets on a sheltered rocky shore and on an exposed rocky shore.

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A study on the limpets density between a sheltered rocky shore and a exposed rocky shore Aim: To investigate the difference in density of limpets on a sheltered rocky shore and on an exposed rocky shore Introduction: "Patella vulgata seems the most ubiquitous of macroscopic shore animals at Dale."2 Limpets are one of the most abundant species in Dale and live quiet and solitary lives. They are of the Mollusca phylum and of group Gastropoda. Their Latin name is Patella vulgata. As with all organisms, limpets are affected by two main factors, * ABIOTIC FACTORS * BIOTIC FACTORS Abiotic is an ecological factor which is concerned with the non-living part of the environment. Abiotic factors are usually density-independent. That is, it doesn't matter how many organisms you have in a particular area, abiotic factors will affect them all. If conditions become hot and dry, for example, it is likely that all the plants of a particular species growing in the area concerned will be affected. It will not matter if the species is extremely abundant or very rare.1 Biotic is an ecological factor which is concerned with the activities of living organisms. Predation, food availability and competition are all examples of biotic factors which will affect the distribution of various organisms. Biotic factors are usually density-dependent. That is, they are factors whose effects on a population are relatively greater at higher population densities than at lower ones.1 Patella vulgata is found wherever there is substratum firm enough for its attachment on rocks, stones and in rock pools, from the high shore to the sub littoral fringe. It is abundant on all rocky shores of all degrees of wave exposure although the highest densities of Patella vulgata coincide with wave exposed conditions. ...read more.


From the results above I thought that the best height to conduct the experiment would be at 3.5 m. I chose a slightly lower value than the one of the preliminary experiment because I found out that the closer to shore you got the higher the density of limpets, and also allowed myself enough time to get the readings before the tide came in. When deciding on the number of samples to take I considered the implications of taking to little or too many. Too little wouldn't allow me to make accurate and concise conclusions about my results and too many would be too time consuming. Knowing that my quadrat was half a metre square in size, I decided that I would take as many samples as possible in an hour, this way I could keep my timings as well as having a sufficient amount of results to base my conclusions upon. Safety was taken into account by filling out two working information cards for both sites that samples will be taken from, Frenchman's Steps and Castle beach bay. These contain information about nearest telephones, escape routes etc. Looking at the size of the beach it was decided that a 30m transect would be the most appropriate length of transect. This would allow a big enough area to survey and give a good set of results for that site as the sampling wouldn't be localised to one area but spread across much of the beach. Random sampling would be the best sampling technique for this investigation as I will be able to generate random coordinates across the 30m tape. The random coordinates are generated using the RAN# key on a calculator and multiplying the number by 30. Locations Castle Beach Bay - Grid Ref. ...read more.


This means that more salt is carried and so the result is a high salinity level which doesn't help the limpets. The limpets that are larger often survive better than those that are smaller, again accounting for the small population at this point. Theses harsh abiotic conditions do not favour the diversity of life as only one type of seaweed was present, the bladder wrack. Other species of animal were also hard to find. We can say that the level of nutrients at this shore must also be lower as the observed diversity of life was also lower explaining the amount of limpets to be lower than at Frenchman's steps. Evaluation It is clear from the results that some anomalous results had been achieved, i.e. finding 3 limpets in one quadrat at Frenchman's steps. These anomalous results could be explained by rock pools. These microhabitat often offer a less hostile environment, but the level's of competition inter and intra specifically are also high/. Meaning that at these places the populations of limpets would experience less numbers accounting for the anomalous result. If I was to repeat this experiment again, I would take picture of every quadrat sample I took, so that I could easily check if results seemed a bit wrong. I would definitely have to spend a lot more time on counting because we were working with a time limit and this could have cause inaccuracies to arise. An element of error could have been present on when measuring the chart datum. One could never be sure exactly where it was so estimates were taken and the readings done from there. This added to the level of error of the experiment. To overcome the problem of timings, I would have liked to do the readings at the same time, i.e. on separate days. 4- http://www.marlin.ac.uk/species/Patvul.htm Biology Investigation Jasdeep Bahra - 1 - ...read more.

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