# Investigation on the shape and size of limpets on a sheltered rocky shore called Frenchman's steps beach.

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Introduction

Rukjit Randhawa

A2 Biology Coursework

Investigation on the shape and size of limpets on a sheltered rocky shore called Frenchman’s steps beach.

PLANNING:

Aim:

To investigate the height and base of limpets at two different vertical heights from chart datum, on a sheltered rocky shore.

Introduction:

The aim of this experiment is to determine whether there is a difference between the height and width of the limpets, at 2 different points on a beach profile in their vertical range. Limpets are distinctive animals, which have oval shaped shell; with the peak more-or-less near the centre they are best known for their ability to cling onto rocks.

Limpets are species, which come from the super kingdom, called Eukaryotea, and followed by the kingdom called Animalia down to the phylum called Mollcusca and finally it is part of the class called Gastropods, (14.4).Gastropods, which are shelled animals with a single large foot that encases the animal's stomach. The limpet has a soft body, with a large foot and a small head with two antennas. They have a brown and white coloration on their shells, which are hard and cone-shaped with a rounded, off-centre point. Special muscles attach the limpet to its shell at the base of the point. The colour of the limpet changes as you go from the upper part of the shell to the middle of the limpet, the underside of empty shells are bluish white with a dark brown centre.

Below is a diagram of the underneath view of a limpet.

Limpets are able to cling to the rock very tightly, they do not have suction, but their strong muscular foot can grab small imperfections in the rock surface, and grasp very strongly.

Middle

17

26

0.65

17

26

0.65

14

8

29

0.28

34

45

0.76

15

5

12

0.42

23

25

0.92

16

6

10

0.6

23

32

0.72

17

6

18

0.33

14

24

0.58

18

12

45

0.27

20

35

0.57

19

10

30

0.33

17

28

0.61

20

12

30

0.4

16

21

0.76

21

10

27

0.37

19

27

0.70

22

5

20

0.25

31

34

0.91

23

12

27

0.44

22

16

1.38

24

8

31

0.26

29

37

0.78

25

10

49

0.33

30

44

0.68

Total

240

668

9.51

563

833

17.28

Above I measured the height and base of 25 limpets I then used that information to work out a height: base ratio, which I did by dividing the height by the base. This tells me for every 1mm the height increases the base increases by the number in the height/base ratio column.

Example: for sample number 1 in the table, the height/base ratio is 0.43:

Height = 10 Base = 23

10 = 0.43

23

Now I have found the height/base ratio for each limpet, I can use this to find if there is a statistical difference between the height and base of limpets at 2 different height on a sheltered rocky shore. To find a statistical difference I will be using the T-Test, I choose this test because a T-Test is used when you want to see if 2 means are significantly different. I will be looking at the means of the height/base ratio of limpets at 3m and at 6m. I will also be using the result of the T-Test to accept of reject the null hypothesis.

The following equation is used to work out the value of the T-Test

t = X1 - X 2

√ S1 ² + S1 ²

n n

X1 : stands for the mean for the first set of data which is the mean of the limpets at 3m.

X2 : stands for the mean for the second set of data which is the mean of the limpets at 6m.

The equation to work out the mean is

Mean = Σx/n

S1 ²: stands for the variance for the first set of data which is the variance of the limpets at 3m.

S2 ²: stands for the variance for the second set of data which is the variance of the limpets at 6m

The equation to workout variance is

Variance (s²) = Σx² - (Σx) ²

n

n – 1

I am now going to work out the t value using my results above in the table, to do this I need to work out the Σx² for both sets of data, which is required when the variance needs to be calculated, which I will do in the table below.

N | X1 | X1² | X2 | X6² |

1 | 0.43 | 0.1849 | 0.68 | 0.4624 |

2 | 0.42 | 0.1764 | 0.66 | 0.4356 |

3 | 0.38 | 0.1444 | 0.66 | 0.4356 |

4 | 0.29 | 0.0841 | 0.48 | 0.2304 |

5 | 0.42 | 0.1764 | 0.51 | 0.2601 |

6 | 0.3 | 0.09 | 0.64 | 0.4096 |

7 | 0.54 | 0.2916 | 0.61 | 0.3721 |

8 | 0.35 | 0.1225 | 0.61 | 0.371 |

9 | 0.43 | 0.1849 | 0.44 | 0.1936 |

10 | 0.33 | 0.1089 | 0.64 | 0.4096 |

11 | 0.3 | 0.09 | 0.62 | 0.3844 |

12 | 0.39 | 0.1521 | 0.71 | 0.5041 |

13 | 0.65 | 0.4225 | 0.65 | 0.4225 |

14 | 0.28 | 0.0784 | 0.76 | 0.5776 |

15 | 0.42 | 0.1764 | 0.92 | 0.8464 |

16 | 0.6 | 0.36 | 0.72 | 0.5184 |

17 | 0.33 | 0.1089 | 0.58 | 0.3364 |

18 | 0.27 | 0.0729 | 0.57 | 0.3249 |

19 | 0.33 | 0.1089 | 0.61 | 0.371 |

20 | 0.4 | 0.16 | 0.76 | 0.5776 |

21 | 0.37 | 0.1369 | 0.70 | 0.49 |

22 | 0.25 | 0.0625 | 0.91 | 0.8281 |

23 | 0.44 | 0.1936 | 1.38 | 1.9044 |

24 | 0.26 | 0.0676 | 0.78 | 0.6084 |

25 | 0.33 | 0.1089 | 0.68 | 0.4624 |

Total | 9.51 | 3.8637 | 17.28 | 12.7366 |

Conclusion

To extend this investigation or to provide additional evidence for the conclusion and to overall make my investigation more accurate I could. Compare the abundance of Limpets on a sheltered and exposed rocky shore, 3m and 6m above chart datum. I could compare the size of Limpets 3m and 6m above chart datum, with distribution of green algae, on the exposed and sheltered rocky shores. This will show me how important food which is green algae was for the growth of limpets. I could also compare the density of Limpets at different vertical height above chart datum, with another animal such as barnacles, on the exposed and sheltered rocky shores. Since barnacles can be found on the limpets outer shell.

Overall I am pleased with my investigation, and pleased with my results and conclusion, and am happy to reject my null hypothesis and conclude that limpets present on the vertical height of 3m are smaller than the limpets present on the vertical height of 6m. However there is always room to extend and improve my investigation which will increase the reliability of my results and conclusion.

BIBLIOGRAPHY

I used the following books and websites whilst doing my investigation on the shape and size of limpets on the rocky shore:

- Further studies in biology,

by Margaret Baker

Bill Indge

Martin Rowland

- Understanding biology for advanced level,

by Glenn Toole

Susan Toole

- Biology,

by Ann Fullick

- www.wildlife.shetland.co.uk/other/algae_limpets.htm

- www.ourworld.compuserve.com/homepages/BMLSS/Limpets.htm

- www.mesa.edu.au/friends/seashore/limpets.html

- I have used blue highlighted numbers in my investigation to indicate which part from the AQA 2004 biology specification A. course I have included in my investigation.

This student written piece of work is one of many that can be found in our GCSE Height and Weight of Pupils and other Mayfield High School investigations section.

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