An investigation into the distribution of adult and juvenile limpets on a rocky shoreline.

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A2 Biology coursework- Section A (Planning)                                       Crystal Tsui


An investigation into the distribution of adult and juvenile limpets on a rocky shoreline.


Limpets are animals that belong to the family Patellidae. They are commonly found attaching strongly to rocks. In this study, it will be possible to assess the effect of shore height on the distribution of adult and juvenile limpets. The biotic and abiotic factors will be taken into account on their distribution on different shore heights, i.e  lower shore, middle shore and upper shore. I am going to carry this investigation at Cullercoats Bay, North Shield.

On different shore heights, the abiotic and biotic conditions are varied which affects the distribution of adult and juvenile limpets.

Abiotic factor

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). 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.

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.

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 .

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. The wave action causes the shell muscles to contract vigorously, clamping the limpet on the rock, therefore, they must develop stronger feet, smaller and more streamlined shapes.

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. 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.

Biotic factors

Competition: It can either be interspecific  or intraspecific . 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 short as the conditions are better. Also, as there are more algae and seaweed on the lower shore which means a keen competition.

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.

Microalgae → Limpets→ Dog whelks

 As limpets feed on microalgae, they are likely to be fund where there is a greater percentage coverage of microalgae .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. A predator-prey cycle is shown as following.


H1: There will be a significant difference between the number of adult and juvenile limpets found on the upper shore and lower shore.

H0: There will be no significant difference between the number of adult and juvenile limpets found on the upper shore and lower shore.

H1: There will be more juvenile limpets found on the lower shore.

H0: There will be no more juvenile limpets found on the lower shore.

H1: There will be more adult limpets found on the upper shore.

H0: There will be no more adult limpets found on the upper shore.

H1: There will be more limpets found on the middle shore.

H0: There will be no more limpets found on the middle shore.

I am going to use the following equipments in my investigation.

Safety Assessment

  1. In order not to get cut off by incoming tides, I should check the tide time and to be aware of the sea ‘s position.

  1. I should place the quadrat down carefully and sensibly so as not to damage the limpets or other organisms. Do not move any limpets.

  1. Wear suitable footwear and clothing due to the rocky surfaces and weather fluctuations.

  1. I should always work in pairs so that I can contact/seek help once accident occurs.

  1. I should not push/trample over the limpets or their habitat and make sure I am not endangering any other plants/organisms.


Independent: Vertical height above chart datum (Lower shore, middle shore and upper shore)

Dependent: Number of adult and juvenile limpets distributed on different shore height.

There will have to be some factors that will have to be controlled to make this investigation a fair test and obtain valid data.

  • Temperature: This factor cannot be really controlled by me due to weather fluctuations in an outside environment, but the investigation procedures will be carried out on the same day and some tide period, this can ensure the temperature is as constant as possible.

  • Make sure the same person is holding the same piece of equipment so that any errors will be a fixed error and is cancelled out.

  • Make sure the cross staff and ranging pole is straight when holding on the shore, also, the surface should be flat but not a rock or a hole. It is because the would affect the independent variable – the shore height.

  • The tape measure should lie as straight as possible all the way along the same height. I will use some stones to make it fix. The purpose of it is to ensure the samples that I will be collected are on the same shore height level.

  • The amount of samples collected from lower, middle and upper shore will have to be the same. I will collect 30 samples at each shore heights so as to ensure a fair test.

  • The quadrat may not be lied very flat due to the rocky surface so I will count the limpets within the quadrat as accurate as possible. Also, if the sample area is a rocky pool or a big rock, I should skip that particular area to the next because there is a larger surface area for the rocky pool and smaller surface area for the big rock, the shore height level at these area would also be different which makes the data invalid.

  • I should also make sure I will not count the other organisms which look similar to limpets such as barnacle because this will make it an unfair test.



Definition of an adult / juvenile limpet

I need to make a valid cut off size foe what a juvenile or an adult limpet is before the investigation. I think 20mm is a fair cut off size to decide whether the limpet is an adult/juvenile. I am going to use a calliper to measure the base diameter of the limpet. Any limpets’ base diameter is < 20mm will be considered as a juvenile whereas >20mm would be considered as an adult limpet.


1. Once I get to the shore at about 11:30 am, it will be a period of low tide.  I am going to use the cross staff, ranging pole and meter ruler to measure my first shore height at the point where it is 1.1m above the chart datum which is a level so low that the tide will not frequently fall below it. The following diagram will help me to explain how this technique works.

2. From the above diagram, one person will be holding the cross staff, another person will be going up to the higher shore height with a ranging pole. Place the cross staff on the height of 1.1m above the chart datum and then looks along the cross staff, using the spirit level to ensure that it is on the eye level, the person holding the ranging pole will then move the hand up or down the pole until reaching the spoted point where  in  line with ‘ 1 meter ‘ , then use the meter ruler to measure the height between that point and the ground, this gives a value of  a ,then 1- a = b, therefore, the first shore height of a lower shore will be b + 1.1 m .

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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, ...

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