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Limpet Size Investigation

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´╗┐LIMPET SIZE INVESTIGATION Aim: To investigate if the width of limpets varies at different heights above chart datum. Site: Jetty Beach (Sheltered rocky shore) Grid Reference: SM 823053 Aspect: North North East Date: 03/06/12 INTRODUCTION Jetty beach is a sheltered rocky shore with rich biodiversity, predominated by solid rocks. It consists of a range of microhabitats including bare rocks, rock pools, crevices and seaweed, providing secure habitats for a variety of organisms such as seaweeds, barnacles, shells and limpets. It is divided into four tidal levels ? the lower shore, middle shore, upper shore and splash zone. The lower shore (up to 2.5m above chart datum) is 0-20% emersed and faces low desiccation. The middle shore (2.5m to 5.2m above chart datum) is 20-80% emersed and faces more desiccation than the lower shore. The upper shore (5.2m to 7.8m above chart datum) is 80-100% emersed and faces more desiccation than the middle shore. The splash zone (more than 7.8m above chart datum) ...read more.


Five quadrats are placed along each height at intervals of 1m, and 5 limpets were selected to be measured from each quadrat. In total, we collected 25 samples from each height. The independent variable in this investigation is the height on the shore above chart datum, and the dependent variable is the width of the limpet shell. Equipment: A 0.5m2 quadrat, a metre ruler, an optical level, a pair of Vernier callipers and a tape measure. ANALYSIS We used a t-test to see if the means from our data are significantly different. The null hypothesis (Ho) for this t-test is that there is no significant difference between the mean widths of Common Limpets at different heights on the shore above chart datum. Sample number Height above chart datum 2.0m 4.0m 6.0m X(l) X(l)2 X(m) X(m)2 X(u) X(u)2 1 3.50 12.25 1.82 3.31 2.52 6.35 2 1.20 1.44 2.17 4.71 1.89 3.57 3 4.00 16.00 1.96 3.84 1.79 3.20 4 2.00 4.00 1.35 1.82 2.61 6.81 5 2.52 6.35 1.22 1.49 3.05 9.30 6 1.59 2.53 2.22 4.93 ...read more.


is less than the critical ?t? value (2.021), hence we accept the null hypothesis with 40 degrees of freedom at the 5% significance level. The calculated t value ?t2? (2.900) is greater than the critical ?t? value (2.021), hence we can reject the null hypothesis with 6 degrees of freedom at the 5% significance level, and accept the alternative hypothesis that there is a statistically significant difference between the mean widths of Common Limpets at 4.0m and 6.0m on the shore above chart datum. INTERPRETATION CONCLUSION EVALUATION Limitations and Improvements: 1. Our selection of limpets to measure from each quadrat was not random and was subject to human bias. To improve, we could have produced random numbers with a calculator and measured the limpet that is closest to each random value along the tape measure. 2. The width of the limpet is not solely dependent on the height of the shore above chart datum and is also dependent on other factors such as the age of the limpet and its microhabitat. 3. On the upper shore, the number of limpets is very small and some of our quadrats had not enough limpets for us to measure. ...read more.

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