(6) Pratical Statistics for Field Biology, second edition, Jim Fowler, Lou Cohen, Phil Jarvis, published 1998, page 138 and 238.
(7) Genetics, Evolution and Biodiversity, John Adds, Erica Larkcom, Ruth Miller, published 2001, page 31 and 32.
(8) Life on the sea shore, John Barret, published 1974, page 72 and 73.
(9) Marine Biology, James W Nybakken, Mark D Bertess, published 2003, page 245.
(10) Sea Shore, Peter J Hayward, published 2004, page 119-122.
(11) http://www.multimap.com/maps/
(12) http://www.acadat.com/HLC/milford/area/341.htm, Adapted from
Sea Grant Publications, University of California.
(13) http://en.wikipedia.org/wiki/Intertidal_zone
(14) http://military.coastline.edu/classes/biology100/image1.gif
(15) http://en.wikipedia.org/wiki/Spearman's_rank_correlation_coeffic ient
Outline Plan:
Hypothesis:
The height: width ratio of limpets will increase with distance from the sea.
Method:
I will use a belt transect of the entire length of the rocky shore, divided into equal intervals of 2 meters to establish how the height to width ratio of Limpets changes with distance from the sea, this is a form of systematic sampling. Due to the distance that will need to be considered, I have chosen to divide the distance by two and work at intervals of 2 meters in order to cover the length of the beach within the time period I will have available.
- I will measure the profile of the beach using two ranging poles tied together with a 1 meter length of string. Starting at the sea whilst the tide is out, I will position the poles at a meters length so that the string is taught and positioned on the correct mark. Using a spirit level I will adjust the string on the second pole to make it level, and record the difference in the new position of the string and the original marker. This process will be repeated until the back of the rocky shore at the foot of the cliff is reached. I will then be able to accurately replicate the beach profile and will prove to be useful when analysing my results, as this may
- A measuring tape will cover the length of shore from the edge of the sea to the end of the beach. I will then place a 1 meter quadrat at the end of the tape nearest the sea, and record the height and width measurements of 4 Limpets nearest to the middle of the quadrat.
- Using 2 30cm rulers I will accurately record the height of the Limpet by standing one ruler vertically against the side of the Limpet and sliding the second horizontally downwards until it touches the tallest point of the shell, I will then be able to read of the height to the nearest 0.5mm. This is a more accurate way of measuring the height of Limpets as the highest point of the shell is measured.
- The width of the Limpet will be recorded using a calliper, the tips of which will be adjusted to fit the width of the Limpet. I will then remove the device and record the width by using the scale on the calliper which is accurate to 0.5mm.
- Measurements will be taken of 4 Limpets in each quadrat every 2 meters. If there are an insufficient number of limpets to record information from within the quadrat, I will work horizontally at the same distance from the sea to obtain results.
I have chosen to record the height and width measurements of 4 Limpets in each quadrat, as this gives sufficient data to take an average from at each increment from the sea. I plan to measure limpets closest to the middle of the quadrat as this will produce unbiased results and include a greater range of height and width dimensions, rather than using limpets of the same size. Limpet distribution is aggregated; therefore recording one sample will be unreliable. Consequently I will repeat the above method 3 times, in order to gain an appropriate number of results to draw a conclusion from and prove my hypothesis to be correct.
Equipment:
- Measuring tape – This will be used when constructing the shore profile and when collecting results as an accurate distance of the rocky shore can be identified and the correct placement of the quadrat can be made.
- Two 30cm rulers – These will be used to accurately measure the height of each Limpet rather than estimating measurements from one ruler.
- Calliper – This will produce accurate width measurements due to the fact that it has a much higher degree of procession in comparison to a ruler.
- 1 meter Quadrat – The space within the quadrat will contain the Limpets which will be measured and will also be used to work at equal intervals up shore.
- Two Ranging Poles – These are essential in the construction of the beach profile, with a meter length of string between them they will assist in the measurement of the shore angle.
- One meter length of string – To tie between two ranging poles to determine shore profile.
- Pencil/Paper/Clipboard – to record measurements of Limpets.
- Electronic thermometer – to measure the temperature of the air and sea water on the rocky shore.
- Light intensity probe – to determine the level of sunlight the rocky shore is exposed to.
- PH probe – to measure the PH of the sea water.
- Humidity sensor – to measure the water saturation of the air.
I have chosen to use the Spearman’s Rank Correlation Coefficient statistical test; this is the most suitable test as it determines the relationship between two variables. The two variables I will be analysing the correlation between, are the height to width ratio of the Limpet and distance from the sea. As a result of this test I will be able to determine whether my results are higher than 75% in statistical significance. This is a Non-parametric measure of correlation.
Variables:
Key variables that I will need to control throughout the collection of my data are (7):
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Identification of the correct species of Limpet – Patella Vulgata the most common species, taller shells. Patella Depressa shorter shell heights but wider diameter. Due to the Black-footed Limpet being less common, It is unlikely that this species will be present in abundance on the rocky shore I will be collecting results from. Therefore I will not take measurements from this particular Limpet to avoid inaccuracy in my final height to width ratios.
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Age of the limpet – The dimensions of the Limpet shell will be different depending on age. Older Limpets will have a wider diameter, similarly young Limpets will have shorter shell heights. Therefore by measuring height as well, age will prove to be a minimal limitation when analysing my results.
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Identification of live Limpets – The Limpets will not be adhered to rock if dead. When selecting 4 Limpets in each Quadrat I will ensure that all organisms are alive as dead Limpets will not provide sufficient height and width data.
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Limpet Environment – I t is important that I do not measure Limpets covered in seaweed because they are sheltered from the wave action of the sea. Therefore height and width dimensions will differ from that of Limpets exposed to different conditions.
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Profile – the profile of the rocky shore needs to be determined as it will affect my results. By analysing the profile I will be able to account for ridges and troughs in which Limpet height and width will differ. This may be due to less exposure to water or protection from prevailing winds. I will construct the profile and work up shore to ensure that all measurements are taken along the calculated belt transect.
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Predators – Starfish and Seagulls are the most common predators to the Limpet, therefore numbers may be reduced. Adaptations of the Limpet such as clamping down on rocks make them a harder target for their predators. I will control this by collecting data from the same rocky shore within a short time period of 2 days.
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PH/Salinity – I will measure the PH of the sea water using a PH indicator. Sea water has a salinity of 3.5%◦ with a PH ranging from 7.5 to 8.4, which indicates that the water is alkaline; however salinity will vary due to location and the tides. Due to the level of salt in the water, the growth rate of Limpets may be slower; this applies more to Limpets located nearer the sea.
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Light Intensity – Light intensity will be measured using a light intensity probe on the rocky shore. The level of intensity will be important when analysing my results as numbers may be lower due to increased desiccation. Light is a source of energy for seaweed such as Bladderwrack to photosynthesise, therefore levels are likely to be higher in this particular environment.
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Temperature – The temperature of the water and air will be measured using an electronic thermometer. This will indicate the optimum temperature that Limpets can successfully live in. The main source of heat will be from the suns radiation and the presence of vegetation.
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Humidity – the saturation of the air will be measured using a humidity sensor.
All of the Abiotic factors will be observed as little can be done to control them, However they may influence the size, number or growth rate of Limpets on the shore. To introduce minimal control I will collect all results within two days, visiting the shore at the same time on both days when the tide is out. Within this short time period weather conditions are unlikely to have changed dramatically enough to affect my results greatly; however this will be taken into consideration when analysing.
Risk Assessment:
- When working on the rocky shore I will make sure that all movements are made safely, especially when moving over seaweed covered rocks which are slippery which could result in serious injury.
- I must be aware of tides retreating at a rapid rate and if approaching from behind, I will ensure that I progress up shore, or start at the top of the beach at high tide to avoid being swept out to sea and risk of drowning. I will find out tide times before starting the data collection.
- Sea water temperatures are cold at present, therefore slipping on rocks or loose objects into the sea could result in Hypothermia therefore measures will be taken to ensure this risk will be minimised, such as working on the rocky shore at high tide.
- I will ensure that I do not walk directly under cliff faces, to minimise the risk of falling objects causing a serious injury.
- I will regularly drink fluids whilst working on the rocky shore to prevent dehydration.
- Due to the risk of illness I will wash my hands thoroughly before eating or drinking. I will be working with live organisms and seaweed which could carry parasitic organisms or be contaminated by other substances or chemicals carried in the water.
- There may be bits of broken glass and other litter may be scattered on the rocky shore, therefore care will be taken when manoeuvring over the rocks.
- I will ensure that Limpets are not disturbed in their natural environment, by not removing them from the rocks as measurements can be taken with Limpets in their favoured position, if any do separate from their substrates I will replace them in their original position. I will also take care when walking over the seaweed, avoiding it completely if possible to prevent damage to both frongs and bladders.
Method:
I will use a belt transect divided into equal intervals of 2 meters to establish how the height to width ratio of Limpets changes with distance from the sea.
- The profile of the beach was established using two ranging poles tied together with a 1 meter length of string. Starting at the sea whilst the tide was out, I positioned the poles at a meters length so that the string became taught and was positioned on the correct mark on the ranging pole. Using a spirit level I adjusted the string on the second pole to make it level, and recorded the difference between the new position of the string and the original marker. This process was repeated until I reached the back of shore at the foot of the cliff (62 meters in length). I was then able to accurately replicate the beach profile which was proved to be useful when analysing my results, as ridges and troughs were determined, in which Limpet sizes and numbers differed.
- A measuring tape will covered the length of shore from the edge of the sea to the end of the beach. I then placed a 1 meter quadrat at the end of the tape nearest the sea, and recorded the height and width measurements of 4 Limpets nearest to the middle of the quadrat.
- Using 2 30cm rulers I will accurately recorded the height of the Limpet by standing one ruler vertically against the side of the Limpet and sliding the second horizontally downwards until it touches the tallest point of the shell, I will then able to read off the height to the nearest 0.5mm. This was a more accurate way of measuring the height of Limpets as the highest point of the shell is measured.
- The width of the Limpet was recorded using a calliper, the tips of which were adjusted to fit the width of the Limpet. The device was then removed and the width was recorded using the scale on the calliper which is accurate to 0.5mm.
- Measurements were taken of 4 Limpets in each quadrat every 2 meters. If there were an insufficient number of limpets to record information from within the quadrat, I worked horizontally at the same distance from the sea to obtain results.
Table of Results:
Results:
Statistical Test (Spearman’s Rank Coefficient Correlation):
A null hypothesis is established in order to support the original hypothesis. The null hypothesis will be presumed true until statistical produced from conducting the Spearman’s Rank Coefficient Correlation, indicates otherwise.
Null Hypothesis:
The height to width ratio of Limpets is not affected by the distance from the sea. (6)
The two variables that I intended to find a similarity between were how the height to width ratio of the Limpet varies with distance from the sea.
Method:
- A table was constructed which indicated the distances from the sea at which results were recorded and the average height to width ratio calculated from both repeats at each site. In the case of 4 sites, no results were recorded; therefore these were not counted in the statistical test. When distances were listed and ranked, only 23 were used. The height to width ratios were all rounded to one decimal place in order to make ranking the values easier.
- Both distance from the sea (rank one) and Height to Width ratio (rank two) were ranked in order (highest to lowest), if there was more than one result that had the same value, both results were added together and the total value was divided by the number of results concerned.
- I then found the difference between the two ranks (d). This was calculated by simply subtracting the first value of rank one from the first value in rank two. This method was repeated for the remainder of the results and produced both positive and negative results.
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Finally to discount the negative values, all values were squared to produce positive integers (d²).
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The total of all values in the final column represents the value of Σd².
Using this information, I then substituted the calculated data into the equation below. From this I was able to determine the statistical significance of my results taking into account the number of sites that were tested:
(15)
Subtracting 1 from the whole equation represents the degree of freedom, which accounts for the error in the calculation.
Data:
Σd² = 511.5
Statistical Result =1-(6 x 511.5)
233 – 33 = 0.931513
With reference to a statistics guide, I was able to find the critical values to 90%, 95% and 99.9% significance, correct for the number of sites I collated information at. This was used as a comparison against my final value to determine the overall significance of my results.
(6)
As a result, I can conclude that my results are 99% significant and consequently I can reject my null hypothesis as my original is supported.
Analysis:
It is evident that there is a positive correlation between the height: width ratio of Limpets and the distance from the sea. The average ratio found nearest the sea was 0.7 and as distance increased to 54 meters, height and width measurements of the Limpets also enlarged producing a ratio of 1.3. As indicated on the line graph displaying the average ratio every 2 meters from the sea, there are dips in trend which indicate either a change in environment, Abiotic factors or error in the accuracy of recording the results. When producing my line graph I did not include distances at which no results were recorded, therefore there are unequal intervals along the ‘x’ axis.
The height: width ratio begins to increase until distance from the sea reaches 4 meters. At this point the ratio decreases to 0.8 at 6 meters and 0.4 at 8 meters, this can be accounted for due to a small trough in the form of a rock in the beach profile. Limpet height and width increases further to 1.0 where it remains constant for 6 meters at 16 meters the ratio decreases for a second time to 0.8, this is also due to a larger trough in the beach profile. This trend continues to increase consistently into a third trough is reached at 46 meters where the ratio decreases from 1.1 to 1.0, from this point onwards the height and width measurements increase to 1.3 were they plateau.
Two anomalous results that I have identified are at 20 and 22 meters from the sea. There is no dramatic change in the beach profile; however, at this distance the beach became flatter and a large amount of Bladderwrack and Eggwrack was found to be covering the Limpets. My original method stated that I would work horizontally at the correct distance from the sea to obtain measurements, but this was not possible as the seaweed covered a large expanse of the flat shore. Therefore measurements were taken from Limpets that were covered in seaweed and consequently would be smaller in both height and width.
Abiotic factors on the sheltered rocky shore were observed and recorded on the first day of result collection. Temperature of the sea water was 10.1ºC and the temperature of the air was 13.9ºC, due to the time of the year the water was colder than the air. Humidity was recorded at 66.7% and light intensity measured 38,876 lux, both of which were expected when taking the weather conditions into consideration. The last Abiotic factor that was measured was the Ph of the water found in the sea (Ph 8.9) and in rock pools on the rocky shore (8.1). It was expected that water in the rock pools in slightly less alkaline due to Ph decreasing with distance from the sea. There was very little wave action due to weather conditions being favourable and the rocks on the shore reducing wave impact. Although these results were only collected on the first day of the investigation, weather conditions did not change considerably over night and were therefore not expected to differ largely, which confirms my previously discovered background information.
Limpets were not present higher then 54 meters on the rocky shore due to the splash zone not being submerged in water, and Limpets cannot successfully live in these conditions.
Discussion and Evaluation:
My investigation proved to be successful and my hypothesis was correct. The height: width ratio of Limpets does increase with distance from the sea and my results support this conclusion.
As a general trend the width of the Limpet shell will not exceed its height. Due to the rocky shore being sheltered, the height: width ratio increased which indicates that the shells are taller rather than wider. Limpets are able to grow taller as they are at less of a risk from predators such as Sea Gulls and therefore do not need to be streamlined to their substrate. Limpets found nearer the sea are expected to be smaller due to their age. Older Limpets migrate up shore with age, whereas the younger limpets are located within the sub-littoral zone as the larvae are suspended in the sea before securing themselves to a hard surface.
Due to the protection offered by the sheltered shores, the Limpets were not exposed to such consitions that their shell was wider rather than taller consequently lowering the hieght: width ratio, which is what would be expected on an exposed shore. Large rocks and other beach material acted as a break for previaling winds and destructive waves, consequently minimising the chance of becoming separated from their substrate.
Three anomilies identified are due to the profile of the rocky shore, troughs that followed large peaks contained limpets of smaller dimensions due to the absence of abiotic factors such as sunlight and warmer air temperatures. The two conistantly low results at 20 and 22 meters from the sea where the result of Seaweed covering the Limpets, consequently reducing their exposure to light intensity. The seaweed demonated the rocky shore in a relativly flat location within the littoral zone, a suitable location because of the hourly tidal pattern resulting in this zone being submerged in water.
Repeats were taken once and when analysing both sets of data, it was evident that they both indicated the same trend. My satitistical test and line graph were both produced using an average from both origional and repeated data. After conducting the Spearmans Rank Correlation Coefficient, I was made aware of my results statistical significance, and consequently I can reject my null hypothesis and conclude that my results are 99% significant.
VARIABILITY BETWEEN REPEATS – ACCURACY
The greatest limitation was measuring the limpets; using callipers
would normally give a very accurate measurement, however as the
limpets were all on rocks, I could not arrange the callipers in a way
that held the entire limpet. As a result estimation was involved when reading the correct width measurements. Another difficulty when concerning the measurement of the Limpet shell was measuring their heights. Two rulers were used as this was the most accurate method and equipment available, however due to the angle at which the Limpets are attached to their substrate at and the angle of the shell, reading an accurate measurement was almost impossible. Both of these methods are likely to have a certain degree of inaccuracy but the imprecision is only expected to be incorrect to the nearest millimetre and will not affect the reliability of my data greatly.
Another limitation that should be taken into consideration is the time period in which the information was collected. The original results and the repeats were collected on different days and weather conditions were not recorded on the first day of data collection. Therefore a change in most Abiotic factors that were observed is almost definite. However this too, is not likely to affect my results considerably as I was never able to control the Abiotic factors, I only planned to observe them and would not have been able to control their changes unless all results were collected on the same day. However, this would not be feasible due to the tide times and the time period needed to collect a sufficient amount of data.
When repeating the investigation, I may have measured the same Limpets as before, which would explain why some of my repeats were the same as my originals; therefore my repeats were not 100% accurate.
To improve this investigation, a third set of repeats would have been made in order to further increase the accuracy and reliability of my results. This would be made easier if the Limpets which were measured each time were marked in some way, so that they would not be included in any repeats but ethical implications would suggest that this would not be fair. Also by repeating the measurements at distances which did not produce consistent results, would indicate if there was an error of judgement or if there is an Abiotic factor affecting the lower measurements. I would also use a more accurate device to measure the shell height such as a specialised calliper, as this would ensure that the error of estimation is reduced.
By conducting the same investigation on an exposed shore, a comparison could be made against the two and conclusions could be drawn considering the different factors affecting the growth of Limpets. Also by analysing the differences in beach profiles I can determine how the absence of large rocks affects the Limpets d imensions and