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An Investigation Into the Effect of Wave Exposure on the Volume of Limpets

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An Investigation Into the Effect of Wave Exposure on the Volume of Limpets


The aim of this investigation was to explore the effect of wave exposure on the volumes of intertidal limpets.  Samples of the Patella spp. were measured at 2 different sites at West Angle Bay.  A 0.25m2 quadrat was used to measure along a continuous horizontal belt transect at a fixed vertical height and the base diameter and vertical height of each limpet was measured using callipers.  These measurements were then used to calculate the volumes of each limpet.  The results obtained showed a measurable difference in the volumes obtained at the exposed shore site compared with the sheltered shore site.  The results showed that there was a higher frequency of smaller limpets and a lower frequency of larger limpets at the wave-exposed site than at the sheltered site. Therefore wave exposure has a profound effect on the size distribution of this intertidal limpet species.  The reasons for this are that the effects of wave action are more at the exposed shore site.  As a result of the force of the water’s acceleration increasing at a faster rate than the organisms ability to hold on as an organism grows, wave exposure prevents the distribution of larger limpets.  When limpets are mobile their adhesive tenacity is much less than when they are stationary.  This suggests that due to their reduced tenacity with movement, the Patella spp. may be limited in size by waves at an exposed shore.      


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2h’ which is the formula to work out the volume of a cone.  After the volume of each limpet in the quadrat was worked out, the quadrat was flipped horizontally in order that the investigation took place along a continuous horizontal belt transect at a fixed vertical height.  The quadrat also ran along the same rock stratum.  This was done because different species of limpet could be found on different types of rock and these species could be bigger or smaller than the Patella spp.  This would affect any trends and patterns found in the volumes of the limpets.  The volume of each limpet was worked out in this quadrat and the quadrat was continuously flipped until a running mean was established.  The running mean was calculated after every volume was worked out until half of the results obtained were 2.5% either side of the mean.  The same apparatus and the same method were used on both shores.  It was important to use the same quadrat size on both shores because a bigger quadrat would mean the horizontal belt transect would be larger and therefore a larger section of the shore would be investigated on one shore compared with the other.  This could provide a greater variation in the limpets and also different species may be included in the results.  This investigation was carried out on two consecutive days at the same time in the day, with similar weather conditions observed on both days.
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In order to see if the results obtained are statistically significant, the value of t must be compared with the table of t values (Appendix 3).  The p values at the bottom of this table show the probability that chance alone could produce the difference between the two sets of data.  The p-value used here is 0.05.  The degrees of freedom for this investigation lies between 120 and ∞, which give the critical values of 1.980 and 1.960 respectively.  The t value obtained was 14.8 and is clearly bigger than the critical value for the degrees of freedom.  This means that I can be 95% confident that the difference between the means is significant and therefore the results are statistically significant. This strong probability shows that the null hypothesis has been falsified by the data.  Therefore the null hypothesis can be rejected and the alternative hypothesis accepted.

The statistical test has shown that this hypothesis is correct:

There will be a statistically significant change in the volumes of limpets found on an exposed shore compared with a sheltered shore.

This hypothesis can be rejected:

There will be no statistically significant change in the volumes of limpets found on an exposed shore compared with a sheltered shore.


BRANCH, G. M. 1986. Limpets: their role in littoral and sublittoral community dynamics. Pp. 97-113. In: P. G. Moore & R. Seed (eds.), The Ecology of Rocky Coasts: Essays Presented to J. R. Lewis. Columbia Press: New York.

Todgham A, Boulding E, Megill WM 1997.  Wave exposure effects on the density, habitat selection and size distribution of intertidal limpets species

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