3. Therefore, for every time to measure the next shore height , I am going to place the cross staff at the place where the previous ranging pole was, then repeat the same procedures, get the value of 1- x and add the previous height, this will give the next shore height.
4. I will have to lay out the 25m tape measure on the first shore height level. I will mark sure that the tape lies straight all along the same horizontal height using some stones.
5. In order to get 30 samples on that horizontal line, I will generate 30 random points using my calculator. Using the numbers, I will measure the limpets on these points on the tape.
Steps to use the random mode on a calculator:
1 .Type in 15,(l am going to set it as the maximum steps to flip the quadrat)
2. Press the Ran# button
3.Then press the = button
4.Use this number to measure the limpet on the tape
6. Now take the 0.25m2 quadrat and place it along the starting point of the tape measure, then use the previously generated number from a calculator to flip the quadrat to the left, if it reaches the end of the tape measure, I am going to flip back to the right, also, if there is a rocky pool or a big rock, I am going to skip that area to the next.
7. The number of adult and juvenile limpets within the quadrat will be counted and recorded. Also, if a limpet is 50% or more inside the quadrat, it will be counted, if it is less than 50% it will not be counted so as to give a fair test.
8. When a second quadrat needs to be done at the same station height it is important that the height is the same. Therefore, I shall flip the quadrat to the right so it is at the same height as the first quadrat. The left side of the second quadrat is were the right side of the first was.
Justification of procedures and analytic method
Though cross staff and ranging pole is a simple and fast technique to measure the shore height ,it relies on human accuracy which has a high chance of errors and anomalies. A more accurate equipment could be Theodolite, however, this is very expensive and quite dangerous for us to use as electricity is involved.
Random sampling will be used because it removes biased sample and I can have a lesser control over which areas to be sampled. It is because sometimes we might deliberately avoid areas which are undesirable such as wet and faeces .Therefore, random sampling provides an equal probability of all areas and thus provide more accurate results in terms of the distribution of limpets.
I am going to use chi squared test to analyse my data because it gives an indication to how significant and how accurate of the results are. The t-test can only suitable to be used when the data has a range of measurements, rather than a frequency which is the form of my data will be collected (number of limpets).The spearman’s Rank also could not be used because the data needs to be ranked. My investigation will only provide data of the number of limpets from three different shore height that is not ranked.
Record observations
I am going to use tables as following to record the numbers of adult and juvenile limpets on the lower shore, middle shore and upper shore.
Worked example at lower shore
Then I am going to calculate the mean of adult and juvenile limpets on the three different shore heights. In this example, the mean of juvenile limpet is 264/30= 8.8, the mean of adult limpet is 230/30= 7.7
The data will be represented in a bar chart :
A normal distribution is expected to be obtained, limpets are most abundant in the middle of their vertical range, where conditions are thought to be optimum.
B
Once I will have found the chi-squared number, I can compare it to a significant table in order to find out how significant the results are and either reject the null hypothesis showing that the abiotic and biotic factors affecting the distribution of limpets or I can accept the null hypothesis showing that there is no underlying factors affecting distribution of limpets along different shore heights.
Degrees of freedom
= (number of rows from observed-1)*(number of columns from observed-1)
= (2*1) –( 3*1)
= 2
The significant table below shows that for two degree of freedom, the chi-squared number is well over the 0.01 significant level, making it only 0.1% likely that the results are occurred by chance.
Chi squared test to show whether the distribution of all limpets on the rocky shore heights is random or whether there is an underlying factor affecting the distribution.
Null Hypothesis
There will be no significant difference between the number of adult and juvenile limpets on the lower, middle and upper shores.
O = Observed frequencies
E = Expected frequencies
Table to show the observed and expected frequencies of all limpets found on the three shore heights
E = (592+642+99) / 3 = 444.3
Chi squared test to show the significant of the results collected for the distribution of all limpets on the rocky shore heights
Probability table showing level of significance in comparison to degrees of freedom used
Degrees of Freedom = ( Rows -1 ) ( Columns – 1 ) = ( 2 -1 ) ( 3 – 1 ) = 2
Using a cut off point of 0.05 for two degrees of freedom, it is clear that the chi squared value determined from my results is well above any of the values on the probability table. My chi squared value is 391.65 above the level of 0.1 % significance and so far above the value, thus the results can be classed as being extremely significant. This allows me to reject the null hypothesis and my data has 99.9 % certainity that there is a significant difference in the distribution of limpets between the lower, middle and upper shores. l can therefore assume that there must be some underlying factors affecting the distribution of limpets on the rocky shore heights.
One such factor could be the control of temperature. Thermoregulation is very important for a limpet as if external temperatures are too high, evaporation could cause the cells of the limpets to dry out, and could result in desiccation. This may be one reason why the limpet chooses to habit the lower and middle shores rather than the upper shores. The upper shores are much more exposed to the sun during the day and are left uncovered by the seawater for the longest period of time. The limpet does hold a certain amount of water in its shell to use for respiration when it is uncovered by the sea and although limpets further up the shore are mostly adult and therefore have a much larger shell to hold the water, this water can only sustain them for a certain length of time. If the limpets water supply runs out then the limpet will no longer have sufficient oxygen for respiration enough water to keep the body cells turgid. lf respiration cannot take place then ATP cannot be produced in the Krebs cycle and it will not be able to attach itself to the rock as the ATP provides energy for the muscle contraction. If the body cells do not remain turgid then there will be no support or structure to the limpet's contraction, the orangelles within the cytoplasm of the cells may not function properly therefore not producing the ATP or the enzymes necessary for survival and so the limpet may die.
The limpet also has a strong muscular foot, which allows it to attach tightly to the rock and limit evaporation. The limpet can secrete a sticky mucus which acts as a seal, however this mucus is made from protein, which can denature at high temperature and would therefore become ineffective if the temperature became very extreme, but this is highly unlikely. lf water is lost then the mucus used to seal the shell and keep it watertight may become ineffective and the limpet will be unable to control water loss and will lose more water by evaporation and the limpet face desiccation.
The middle shore had the greatest number of limpets overall. The lower shore, however provided more protection from predators as there was a vast amount of seaweed cover for the limpets to live under, away from the site of birds and other prey and the lower part of the shore was covered by the water for most of the day which therefore limits the chances of desiccation. In this case there must have been a more dominant factor affecting the distribution, such as the wave crash. The strong waves from the sea could overturn rocks and make it difficult for the limpets to inhabit the sea. lf any limpets had managed to inhabit the area the rocks could crush the limpets due to the fierce action of the waves and therefore decrease their chances of survival.
The waves could also remove the films of micro algae, which the limpets feed on leaving them without food. This may be why the limpets have decided to dominate the middle shore.
Competition may also be a reason for this dominance. Limpets in the larval stage will need to inhabit the lower shore in order to receive sufficient food and have a longer coverage of water, therefore there will be less space for adult limpets to inhabit the lower shore and thus the adult limpets will move up the shore where there is less competition for food and space and settle where conditions are still suitable for survival.
The middle shore offers a more equitable range of factors in which to love, as the area does not remain uncovered by the sea water for a long time and when the tide does come, the majority of the power of wave has been lost when the waves break against the rocks on the lower shore. There is also a good coverage of algae and due to the lower exposure of the area to the sun the middle shore is also more moist than the upper shore.
From the raw data, it is clear that there is definite preference for limpets to inhabit the middle shore as 642 limpets were found on this shore during the sampling. The second preference is the lower shore as 592 limpets were found in the sampling but only 99 limpets were found in the upper shore making it the most undesirable part of the shore to inhabit.
Table to show the distribution of adult limpets found on the three shore heights
Null Hypothesis
There will be no significant difference between the number of adult limpets found on the different shore heights.
The chi squared value for adult limpet distribution is 112.819. This is an extremely significant value and is 99.0 above the significance figure fir 0.1 % significance for two degrees of freedom. It is clear that adult limpets are actively choosing to inhabit the middle shore. There is a relatively small difference between the lower and upper shore with a difference of only 34, which possibly suggests that the adult limpets only inhabit these two shores due to the level of competition on the middle shore.
Adult limpets prefer the middle shore due to the harsh conditions exhibited in the lower and upper shore. The upper shore is more exposed and increases evaporation and water loss, possibly resulting in desiccation in severely high temperature. The upper shore is uncovered for the longest time in comparisons to the middle an lower shore, as the sea is first to uncover it and last to cover it. This means that the limpets inhabiting this area need to be well adapted to cope. The adult limpet has a large shell, which contains water to sustain itself whilst the tide is out. However, if the tide is out for too long and the upper shore is left exposed for longer then this water will therefore not be able to used to provided oxygen to the Krebs cycle for respiration, no ATP will be formed and the limpet will be unable to attach itself securely to the rocks and will leave itself exposed to desiccation and predation from seagulls and other prey.
The adult limpet does not tend to favour the lower shore possibly because its large shell increases the chances of the adult limpets being crushed, as rocks are overturned when the tide comes in and out.
There is also a greater amount of competition from juvenile limpets on the lower shore therefore the adult limpets settle in the middle shore where there is less competition for food, space and resources from the juveniles.
The middle shore offers an environment, which is less exposed to the sun and predators, due to its increased density of seaweed in comparison to the upper shore. This seaweed can be used to hide under away from the view of aerial predators and used as a source of food.
Table to show the distribution of juvenile limpets found on the three shore heights
Null Hypothesis
There will be no significant difference between the number of juvenile limpets found on the different shore heights.
The chi squared value for the results collected on juvenile limpets is 419.93. This value is 406.11 above the value given for 0.1 % significance showing that juvenile limpets are actively choosing to inhabit the lower and middle shores over the upper shores.
The juvenile limpets may be inhabiting the lower shore more due to the fact that the breeding season and so the newly born limpets will not have had sufficient time to migrate up the shore. There are fewer juveniles on the upper shore possibly because the further up the shore the juveniles move the more chance there is of the limpets being affected by changes in salinity and increased exposure.
Limpets tend to settle in moist areas, which further up the shore may be areas such as shaded crevices in rocks. In times of heavy rain these crevices fill up with fresh water. An osmosis gradient will be established because of the differences in water potential between the water within the limpet and the water surrounding it. The fresh water will move in via osmosis as water moves from where it is less negative to where it is more negative. The limpet will be unable control the osmosis because there will be such a steep gradient for the water to move down and the limpet cells will increase in volume so much that the cells will burst and the limpet will die. The juvenile limpets also have a much larger surface area to volume ratio and so water is lost more readily via osmosis.
During high temperatures, the limpets may also be at risk of changes in salinity as the high temperatures cause surface water to evaporate, leaving behind the salt. The limpet can only tolerate a certain range of salinity.
Unlike adult limpets, the juvenile limpets cannot make a home scar because its shell is not properly formed, because of this there will not be a fully water tight seal to protect the limpets during high temperature.
The water contained with in the limpets shell and body cells will move out via osmosis into the surrounding saline environment in an attempt to dilute it. In doing this the limpet will be left without sufficient oxygen for respiration and the body cells will be unable to retain their turgidity. The cells will shrivel up, no ATP will be produced from respiration and the limpets will no longer be able to attach itself to rock and will be left exposed to predator attack.
Being further up the shore also exposes the limpets to predators and a lower food supply. Adult limpets can be uncovered for longer as they do not need as much food, because they are no longer growing and they have a larger shell to hold more water. This allows them to hold more oxygen for longer respiration without a renewed supply of water.
The juvenile limpets however needs to eat more often during the day because it has a much higher metabolic rate and the energy relieved from the food is used for growth and needs to be replaced to allow further growth. Therefore, the juvenile limpets need to inhabit an area which is covered by water more often and for a longer duration so they can feed for a much greater period of time.
Table to show the observed and expected frequencies of adult and juvenile limpets on the rocky shore heights
Null Hypothesis
There will be no significant difference between which zone heights adult and juvenile limpets inhabit.
Expected frequency for the lower shore
Adults
Juvenile
Expected frequency for the middle shore
Adults
Juvenile
Expected frequency for the upper shore
Adults
Juvenile
Chi squared test to show the significance of the results collected for the distribution of adult and juvenile limpets on the three different shore heights
The chi squared number is which is above the significance number given for 0.1 % significance indicating that adult limpets do prefer to inhabit different shore heights. Therefore l can reject the null hypothesis and determine that adult and juvenile limpets are occupying different shore heights.
Only a small number of juvenile limpets choose to inhabit the upper shore in comparison to the middle and lower shore. This may be because juvenile limpets could find osmoregulation much more difficult to control than the adult limpets and so may inhabit areas which have more moisture and are covered by the sea water for a much longer period of time.
Juvenile limpets have a much smaller shells in which to retain water for the periods of time which they are uncovered. They also have a much larger surface area to volume ratio and water is lost more readily via osmosis. Osmosis causes the water to move from where it is high in concentration to where it is low in concentration. The water therefore moves from where it is retained in the limpets shell to the surrounding less humid environment. This process becomes more likely as the time the limpets are exposed to the sun increases. Adult limpets can survive the harsh conditions in the upper shore and so can inhabit the area. This is due to them having a much smaller surface area to volume ratio. They have a much larger shell to hold more water and thus sustain themselves for much longer to cope with the time that they are uncovered by the sea.
Percentage of adult limpets on each shore heights
Percentage of juvenile limpets on each shore heights
Percentage of all limpets on each shore heights
Percentage of adult and juvenile limpets on each shore heights
Out of the adult limpets counted on all three of the shores, were found in the middle shore with only in the lower shore and in the upper shore. This shows a high preference for adult limpets to inhabit the middle shore and so the environment of the middle shore must be the best suited for adult limpets to survive.
Out of the juvenile limpets counted on all three shores, were found on the lower shore and were found in the middle shore, with only found in the upper shore. This therefore indicates that juvenile limpets prefer to inhabit the lower and middle shores, where conditions are probably better suited to their survival.
of limpets on the lower shore are juvenile limpets and as the height increased the number of juvenile limpets found decreased. These results might suggest that the juvenile limpets first settle in the lower shore and then begin to migrate up the shore. When they are smaller they are less at risk of being crushed between rocks due to their smaller size so can probably risk inhabiting the lower shore. The lower shore will also provide them with more food, which is needed for their growth. As they begin to need food less often and they grow larger in size they migrate to the middle shore where they are less at risk from being crushed when the tide comes in.
An amalgamation of these two results shows that the limpet prefer to dominate the middle shore. 48.2 % of all the limpets sampled in my investigation were found in the middle shore, with 44.4 % being found in the lower shore and only 7.43 % being found in the upper shore.
Overall patterns, trends and anomalies
Overall the limpets dominated the middle shore in number. Juvenile limpets preferred the lower shore and adult limpets preferred the middle shore with the upper shore being undesirable for both.
There are some anomalous results in my data. In the middle shore , the quadrat 11 contained 3 adult limpets and 2 juvenile limpets which compared to the rest of the results was unusual as the average number of adult limpets is 9 and that for juvenile limpets is 12, this may have been because there was a low seaweed coverage in that area and so there was little protection from the aerial prey and also a low food supply for the juvenile to feed on.
In the upper shore, quadrats 3 and 22 both had high numbers of adult limpets in comparison to the other results gathered. This may have been due to the fact that the area which was sampled fir these two quadrats was situated in the shade of a cliff. This limited the extreme effects normally experienced in the upper shore such as high temperature and lack of water, as the shade provided a much cooler environment which meant water did not evaporate as quickly and therefore desiccation was minimized.
These anomalies and the small scale of my investigation prevent me from making any firm conclusions from the data.
Evaluating Evidence and Procedures
The times of the tide limited the number of sample areas l could do. I had originally planned
to sample 40 areas on each of the three shore heights but had to reduce this number to 30 so I didn’t run out of time. Reducing the number of samples gave me less pf a true representation of the data and provided less data to analyse.
To calculate the height of each shore heights, l used a cross staff and ranging pole. This apparatus does not give a true representation of the shore height because along any one transect line the profile of the land alters. The cross staff does not take this into account and only measures the height of one point. Ideally should have taken the height at each quadrat but this would have been extremely time consuming and I would have been unable to collect all my result before the tide came in.
Discrepancies could also occur if the ranging pole was placed in a crevice or on an out cropping piece of rock, as this would alter the height measurement. This would give an inaccurate height for the three shore lines and may result in samples being conducted in the wrong shore and this would therefore not give an accurate indication of the distribution throughout the three shores. Greater accuracy could be achieved using a more accurate measuring instrument, such as a theodolite. This was not available to me as it is an expensive piece of equipment.
The random sampling technique used very successful. The technique minimised human bias and helped to five a more accurate representation of limpet distribution on each shore height. I decided l would only count the limpets inside the quadrat and those of which half or more of the length of the shell were inside the quadrat. This gave me a strict rule to follow and ensured hat the method was the same all the way through the investigation. However when determining whether to include or exclude a limpet from the count I took a rough estimate using my own judgement, it would have been more accurate way of determining the length of a limpet would have been to taken three or four measurements such as the ones shown in the picture below and then to have taken an average, this average could then have been used to determine whether the limpet was to be counted or not.
Another alternative could be to use the method used for haemocytometer readings. Any limpets on the borders of two sides of the square quadrat would be counted, regardless of how far over the side, and any limpets over the border of the other two sides would not be counted in the sample. The only requirement to this method is that two sides chosen to be included in the sampling must be used throughout the whole of the investigation.
A quadrat is a good piece of equipment to use as it provides you with a fixed sampling area, however some areas which were sampled were not flat and so when sampling a rocky area a grater overall surface area would have been sampled in comparison to a flat surface, it would therefore have been much better to use a square net of 0.25m 0.25m the net would lie over the rocks and take into account the different shape of the land. The following diagrams would explain more clearly.
In order to differentiate between adult and juvenile limpet , I used a 1 cm cut off point. I measured each limpet on its longest side and if it was smaller than 1cm it was classified as a juvenile. The callipers were not particularly accurate as it was difficult to measure the limpets which were under rocks or in small crevices. A smaller instrument would have been better as this would have fitted into the tiny cracks and provided more accurate measurements.
Another more accurate measurement to use could have been the classification of limpet age by volume. This would have taken into account the different shape of limpets, as a longer flatter limpets would have been classed as an adult using length measurement when it could have been the same length as a taller and thinner limpet which would have been classed as juvenile. A piece of plasticine could have been used to find the volume by moulding it over the shell of the limpet and then finding how much water would fit in the area created when the plasticine was lifted off.
Furthermore, it would have been better to have conducted the investigation every month for a year. This would have allowed for a whole year ’s cycle in a limpet ’s life and therefore would have taken into account the breeding season and all four seasons during the year, which may all have an influence on distribution. My investigation was conducted on one day out of the whole year and so no reliable conclusions can be drawn from the results as the conditions on that one day may have influenced the distribution. The areas where the limpets were found on that day mat not be their true habitat.
Extensions to the investigation
The percentage cover of different species of seaweed, such as the Fucus species of seaweed could be calculated. Here the same method of random sampling could be used, but instead of counting the number, the area covered by each species would need to be estimated using the small squares in the quadrat as a guide, as one square equals 1% in a 0.5m 0.5m quadrat. Seaweed provides a source of food for limpets but also provides a moist environment and a shelter away from the view of predators, so you would expect that a high percentage cover of seaweed would attract a high number of limpets, however too much seaweed could out compete the limpets for space, therefore this factor will probably have a high influence on the distribution of limpets on the rocky shoreline.
The pH of the sea and salinity could be calculated by using litmus paper to test the pH of the surrounding water and by taking a sample of water and later evaporating off the water and weighing the left over salt to calculate the salinity. Limpets can only tolerate a small range of salinity and pH changes, as pH will affect the activity of the enzymes within the limpet, therefore the limpet will probably settle in areas where there is not too great a range of salinity and pH changes.
The distribution of other species of marine animals could be calculated such as barnacles, periwinkles and dogwhelks as these species actively compete with the limpets either for food, space or other resources. Barnacles would need to be counted using the percentage cover method as they appear in vast quantities and live close together, but periwinkles and dogwhelks could be counted using the same method used for limpet distribution.
It is clear that there is an inter-relationship between these factors and the shore heights. It would be interesting to discover if one of the above factors was dominant in its affect on limpet distribution. For example of a high food supply was found in the middle shore but the majority of limpets were settling in the upper shore, the investigation may show that there was a high salinity level in the middle shore, and that this factor had a stronger influence on the distribution than food supply.
Analysis of the Bar Chart
The value of the standard deviation quantifies the spread of the data around the mean. The
larger the number, the greater the spread of data around the mean. Therefore the juvenile limpets on the lower shore had the greatest standard deviation having a greater variation about their mean. This means that the environment they live in supported a greater range of limpet sizes.
As can be seen from the bar chart, there is only a small overlap region between the data of adult and juvenile limpets on the lower and upper shore, whereas there is a relatively larger overlap region between the data of adult and juvenile limpets on the middle shore, this indicates that the result of the lower and upper shore is more reliable than that of the middle shore. Also, the smallest range of +/- Standard Deviation is found on the data collected for the juvenile limpets on the upper shore, thus the data on this is the most reliable.
The bar chart shows that a high preference for adult limpets to inhabit the middle shore and so the environment of the middle shore must be the best suited for adult limpets to survive, whereas juvenile limpets prefer to inhabit the lower and middle shores, where conditions are probably better suited to their survival. Most of the limpets found on the lower shore are juvenile limpets and as the height increased the number of juvenile limpets found decreased. These results might suggest that the juvenile limpets first settle in the lower shore and then begin to migrate up the shore.
Only a small number of juvenile limpets choose to inhabit the upper shore in comparison to the middle and lower shore. This may be because juvenile limpets could find osmoregulation much more difficult to control than the adult limpets and so may inhabit areas which have more moisture and are covered by the sea water for a much longer period of time.
The adult limpet does not tend to favour the lower shore possibly because its large shell increases the chances of the adult limpets being crushed, as rocks are overturned when the tide comes in and out.
From the data, it is clear that there is definite preference for limpets to inhabit the middle shore as most limpets were found on this shore during the sampling. The second preference is the lower shore but only 99 limpets were found in the upper shore making it the most undesirable part of the shore to inhabit.
Section E – Synthesis of principles and concepts Crystal Tsui
Limpets are animals that belong to the family Patellidae, they have a strong conical shell, the limpet foot which allows limpets to adhere to the rock surfaces. Both biotic and abiotic factors will determine the distribution of adult and juvenile limpets across different shore height. Biotic factors involve all the other organisms living in the same habitat and interacting each other. Abiotic factors are the non-living factors that will affect the limpet density across the different shore height.
Abiotic factors
Temperature: There is an increasing temperature fluctuations from the lower shore to the upper shore. As land absorbs and releases heat quicker than water does(water has a high specific heat capacity and thus have a constant and stable temperature). Limpets should be able to have adaptation to control the problem of temperature fluctuation on the upper shore so that their enzymes will not be denatured and failed to function properly. A juvenile limpet would not have the ability to withstand the harsh temperature fluctuation on the upper shore due to its high surface area: volume ratio. It would lose heat a lot quickly than a adult limpets. Therefore, it could be a reason that more juvenile limpets will be found on the lower shore where it is exposed for the least length of time and have a better chance of survival in the more constant temperature of the sea water.
Desiccation : The lower shore gets covered by sea water for a long period for time (about 80% of the year ).Therefore, the risk of desiccation is far less on the lower shore. If water is lost by osmosis from the limpet body to the surrounding, gaseous exchange could also be reduced as there is less oxygen availability which is composed by the sea water, the limpet might dry out and die. It is the reason why more adult limpets will be found on the upper shore than juvenile limpets Adult limpets have bigger shells and therefore have bigger capacity to hold(conserve) a greater volume of water than juvenile limpets and thus they can stay out of water for a longer period of time without drying up and use the oxygen available from the sea water for respiration, this making the adult limpets have better adaptation to survive on the upper shore than juvenile limpets. The adult limpets have a higher tolerance level of desiccation ,on the contrary, juvenile limpets are fairly less tolerant to desiccation, Also, for adult limpets ,they have a strongly feet and muscle to clamp to the rock tightly and better seal , this could reduces water loss during the period of emersion. Juvenile limpets must therefore inhabit the lower shore where it is covered by sea water for longer whereas adult limpets have a better ability to survive on the upper shore than juvenile limpets.
Salinity: When the shore is covered by the sea, the conditions are better as the salinity of the sea is constant leaving the water potential of the limpet and the surrounding water at equilibrium. However, on the upper shore, there is a higher probability to be covered by rain water, then a water potential gradient will exist. Water will travel from the surrounding rain water to the limpet cell which might eventually burst .
For this reason, fewer juvenile limpets would be found on the upper shore than lower shore because of their larger surface area: volume ratio.
Wave crash: On the lower shore, there is a higher chance of waves hitting the shore strongly, limpets on this shore are often being hit by the strong waves. However, on the lower shore there are more small boulders and stones whereas on the upper shore and middle shore, there are mainly flat bedrock. Limpets attached to smaller rocks have more chance of being crushed as the boulders get tumbled by the wave crash. Juvenile limpets which they are smaller in size and therefore can fit better into crevices and are less at a risk of being crushed ,thus avoid the wave exposure. Therefore, they have a higher chance to survival on the lower shore than adult limpets do.
Food availability: There is more algae on the lower shore as the wave brings the food to the shore and the moist condition. The limpets would move over the rock taking the algae when the tide comes over. If not, the chance of water loss would be too great and they would dry up. Therefore, limpets must make their home scar in an area that will be covered by the tide for long enough to feed. Although there are more algae and seaweed on the lower shore which also means there is higher competition for food and space ,this could account for the reason why there are less adult but more juvenile limpets on the lower shore. However, on the other hand, since there is more sun light available on the upper shore, this would be benefit the process of photosynthesis of the algae that convert sun energy into chemical energy, algae store this energy as carbohydrate through the process of photosynthesis. As a result, the growth rate of limpets on the upper shore would be faster than the lower shore resulting a higher proportion of adult limpets on the upper shore.
Thermoregulation is very important for a limpet as if external temperatures are too high, evaporation could cause the cells of the limpets to dry out, and could result in desiccation. This may be one reason why the limpet chooses to habit the lower and middle shores rather than the upper shores. The upper shores are much more exposed to the sun during the day and are left uncovered by the seawater for the longest period of time. The limpet does hold a certain amount of water in its shell to use for respiration when it is uncovered by the sea and although limpets further up the shore are mostly adult and therefore have a much larger shell to hold the water, this water can only sustain them for a certain length of time. If the limpets water supply runs out then the limpet will no longer have sufficient oxygen for respiration enough water to keep the body cells turgid. lf respiration cannot take place then ATP cannot be produced in the Krebs cycle and it will not be able to attach itself to the rock as the ATP provides energy for the muscle contraction. If the body cells do not remain turgid then there will be no support or structure to the limpet's contraction, the organelles within the cytoplasm of the cells may not function properly therefore not producing the ATP or the enzymes necessary for survival and so the limpet may die
Biotic factors
Competition: It can either be inter-specific or intra-specific. Organisms on a rocky shore habitat are most likely competing for food and space. It may be possible that the majority of organisms will compete for space on the lower shore as the conditions are better. Also, as there are more algae and seaweed on the lower shore which means a keen competition. Adult limpets can be uncovered for longer as they do not need as mush food as juvenile limpets which are at a higher metabolic rate. The adult limpets no longer growing and have a larger shell to hold more water, therefore, they are being moving towards to the upper shore where there is less competition. Limpets in the larval stage will need to inhabit the lower shore in order to receive sufficient food and have a longer coverage of water, therefore there will be less space for adult limpets to inhabit the lower shore and thus the adult limpets will move up the shore where there is less competition for food and space and settle where conditions are still suitable for survival.
Predation: The size of a population inhabiting a particular ecosystem will be affected by what the prey and predator is. The following can be a food chain to show the organisms affecting limpets.
Micro-algae → Limpets→ Dog whelks
As limpets feed on micro-algae, they are likely to be fund where there is a greater percentage coverage of micro-algae .If there are many dog whelks in an area it would be expected that the population of limpets will be decreased as there is high predation. However, due to the low population the number of dog whelks will decrease and then the limpet population will increase again. Also, on the upper shore, there is low seaweed coverage thus there is little protection for prey and more exposure to predator as well as lower food supply, juvenile limpets are less likely to be found on this shore.
Summary
There are relatively higher proportion of adult limpets than juvenile limpets on the upper shore, however, most limpets are dominated on the middle shore because of the optimum condition there. The harsh conditions exhibited in the lower and upper shore making them undesirable for limpets. The middle shore offers an environment which is less exposed to the sun and predators as well as less at a risk from being crushed when the tide comes in. The middle shore had the greatest number of limpets overall. The lower shore, however provided more protection from predators as there was a vast amount of seaweed cover for the limpets to live under, away from the site of birds and other prey and the lower part of the shore was covered by the water for most of the day which therefore limits the chances of desiccation. In this case there must have been a more dominant factor affecting the distribution, such as the wave crash. The strong waves from the sea could overturn rocks and make it difficult for the limpets to inhabit the sea. lf any limpets had managed to inhabit the area the rocks could crush the limpets due to the fierce action of the waves and therefore decrease their chances of survival.
