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A comparative study of the density of patella vulgata (common limpet) across a sheltered shore and an exposed shore.

Extracts from this document...

Introduction

A comparative study of the density of patella vulgata (common limpet) across a sheltered shore and an exposed shore Aim: - To investigate the limpet density of patella vulgaris (common limpet) across a sheltered rock shore and an exposed rocky shore at the optimum niche level at both shores. Introduction: - Limpets are distinctive animals that are best known for their ability to cling onto rocks. Patella vulgata (common limpet) can be found wherever there is a rock layer firm enough for it to attach to the rocks or stones, this can be from the high shore down to the lowest part of the tide. It is abundant on all rocky shores of all wave exposure. The limpet is usually not abundant on shores where there are large growths of seaweed. The conical shell of Patella vulgata is up to 6 cm long with radiating ridges and the top central or slightly forward. Individuals from the high shore generally have a taller shell and smaller shell length when compared to juveniles and low shore animals. The outer surface of the shell is greyish white, sometimes with a yellow tint, and has crude radiating ridges and well-marked growth lines. The inner surface is smooth and greenish-grey in colour. The sole of the foot is yellowish, dull orange or brown with a grey or greenish tinge. The mantle skirt is fringed with transparent tentacles arranged in three series of different lengths, internal to which lays a complete circlet of gills. Patella vulgata on rock. A mixture of biotic and abiotic conditions will determine the distribution of patella vulgata across an exposed shore and a sheltered shore. Biotic factors involve interactions between different organisms. Abiotic factors are the non-living factors that will affect the limpet density across two shores. Desiccation: - The species is naturally inter-tidal and in ideal conditions maybe found up to the high tide level and is therefore fairly tolerant to desiccation. ...read more.

Middle

If I take ten readings from the exposed shore and twenty from the sheltered shore this would make my investigation unfair and I would probably be unable to reach a conclusion. The accuracy that this investigation is done at also plays a part in keeping this experiment fair. There are a lot of other organisms that will be on both shores, and there are organisms that look similar to limpets. So when counting the limpets I will have to make sure that I do not count an organism that looks like a limpet because this will make it an unfair test. There is no definite way that I can prevent this from happening, so I have to make sure that when I am counting the limpets I do it properly and accurately as possible. Null hypothesis: - The null hypothesis is that there will be no significant difference in the abundance of patella vulgata across a sheltered rocky shore and an exposed shore. Apparatus: - * 50cm by 50cm quadrat. * 1 meter ruler * Clipboard * Spirit leveller * Calculator * 30 meter measuring tape The reason that I am using a 50cm by 50cm quadrat is because it is quite small. Limpets are very small animals so using a large quadrat will be time consuming and I will not be able to get as many samples as I would like. Method: - 1. Before you set out to the shores to conduct your experiment, you have to decide on how many readings you want to take and decide on how you are going to get your random coordinates. The method to use here is to go to the shore and take as many readings as possible within one hour and then do the same on the next shore. To calculate your random digits you can use your calculator, by pressing SHIFT and RAN#*30. ...read more.

Conclusion

The way I had to measure out the distance from chart datum was very difficult and there was a great chance that I could have made an error. The 30 meter transect line that was placed across both shores might not have been 3.5 meters from chart datum all the way through. Again this would make my results inaccurate and the experiment an unfair test. To check if the transect line was 3.5 meters from chart datum all the way through would have been very time consuming, and time was a limiting factor. Also the lack of apparatus, if I had more advanced apparatus that could calculate the distances to greater accuracy this would have benefited my results. Another source of error was my ability to identify limpets. There were organisms that look limpets but are not limpets and if I counted these in my results, it makes my results inaccurate. The only way that I could have got around this problem if there was an expert that came along with me and could have helped me identify patella vulgata. But this is not a practical thing to do. Lack of apparatus had a limitation on my results, we were given no thermometers and pH probes would have been useful. These apparatus could have let me take measurements of the environment, so I could have concluded my results more evidently. There were anomalies in my results. I did get some random coordinates that were next to each other. When I counted the amount of limpets on one coordinate the number was quite high and then when I placed the quadrat on the next coordinate the number of limpets counted was not high. I was expecting that if the sheltered rocky shore was more abundant in limpets then all my sample numbers would have been high, but this was not the case. I think this was because even on the sheltered shore there are micro-habitats that patella vulgata do not prefer to live in. this is why the difference in numbers occurred. ...read more.

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4 star(s)

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This is a detailed account of preliminary and main investigations. Data is clearly presented and analysed. The discussion of the effects of biotic and abiotic factors might have been developed further.

Marked by teacher Adam Roberts 20/08/2013

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