How does the temperature of the water in rock pools affect the distribution of dog whelks and does the change in temperature reflect the change in oxygen levels?

The other thing that temperature affects is oxygen levels; this was going to be my study but would have been too difficult to measure, due to lack of equipment. At high temperature levels (30°C) a study shows mortality rates increase (to 40%); however when given additional oxygen the mortality rate decreases, showing that it is the impact of oxygen which affects the distribution. The protein profiles from dog whelks exposed to increased water temperatures differ from those of the control, but increased oxygen availability alleviates these differences thus increasing the similarity between heat-shocked and control animal protein pattern. This implies a more stable protein metabolism and might explain the increased survival of heat-shocked individuals when extra oxygen is supplied.

Hypothesis and rationale

I predict that temperature will affect the dog whelk and there may be some positive correlation between temperature (of the rock pool) and distribution (the number of dog whelks in the rock pool). ‘However whereas it is commonly reported that the distributions of organisms are correlated with temperature, the causality of the phenomenon is not always clear’  There are several reasons for this, including a change in feeding and a possible reaction to change in oxygen levels. The latter sadly I will have difficulty in determining due to a lack of equipment, and the likely limited variation in temperature.

Due to my research I would expect there to be more dog whelks on middle shore, which means I may need to change my plan after a preliminary experiment. The dog whelk can only survive out of water for a limited period, and it will gradually become desiccated and also die if immersed for too long (it lives in and out of water). I imagine also that the distribution would be a normal distribution (with a peak in the more medium weather conditions) but I don’t think I will be able to test this as we will not be operating under harsh weather conditions (and therefore will not be able to test for extreme cold or heat). Due to the sun I will be able to test if cooler water is preferable to warmer water, but I will not be able to test if cold water or hot water has a detrimental effect.

Plan

Apparatus

A quadrat - used to mark out the area being used for one transect (see above). This is necessary because otherwise the transects would be unreliable, and more dog whelks may be counted than necessary.

A thermometer – to measure the temperature of the rock pool.

Something to record the data on (pen and pencil) – I need to ensure that all my data is recorded accurately and that I can understand it later.

Initial plan

I will adapt what I do depending on the results of the preliminary test, but I intend to take fifteen transects in each area, so that my results are as reliable as possible. These transects will be as random as possible, but they must be in rock-pools for me to assess the temperature and therefore the reliability of the results will be jeopardised somewhat. I will count the number of dog whelks in each pool. The transects were chosen using a random number generator, walking the number of metres shown, and then choosing a rock pool nearest to where we were. There is a high degree of unreliability in this method, but it was difficult to find an alternative.

Variables I cannot control include salinity of water, shadows made by rocks causing cooler water, prey or lack of it, the weather conditions on the day chosen. I cannot control many variables, but I am measuring temperature and number of dog whelks, so these do not need to be controlled.

2 Shows zonation of shore

Preliminary Test

I will go to the rocky shore (Bracelet Bay, the Gower) on Monday 29th June to carry out my experiment. The first thing I will do (using a quadrat) is conduct a preliminary trial to see if my experiment is appropriate. This I will do by taking three random transects of each area of shore-line and counting the numbers of dog whelks in each. The transects give me an area which will be the same wherever I place it, meaning it is fair and reliable. I can make them random by using a random number generator and walking that many metres from a given point.

Change to plan

The results of our preliminary test show it is pointless to measure the distribution of dog whelks on the upper shore, as there are no dog whelks, and no water to measure the temperature of. Lack of water (as mentioned earlier) can cause the dog whelk to desiccate, and therefore no dog whelks would be found here anyway. This could have been anticipated, and the upper shore is mainly dry.

        

Risk assessment

It will be windy on the beach, meaning the walking conditions will be difficult. Also the rocks are slippery due to the seaweed; meaning appropriate footwear must be worn, and due care must be taken. The tide will be coming in, so this is something we must consider, as it will be dangerous, and someone could become trapped. It is also scheduled to be hot and sunny, so we must wear sun-cream, and be sure to drink lots of water.

Results

There are no visible anomalies in the data.

Spearman’s rank

I am going to use Spearman’s rank because I am looking for a correlation (between temperatures of rock pools and distribution of snails), and this is the most efficient statistical way of doing this. I can discount using T-test because no normal distribution can be seen, although if I had a wider range of data this may change. The same applies for the other tests.

Spearman’s rank correlation coefficient

Null Hypothesis: There is no correlation between temperatures of rock pools and distribution of snails.

p=1-(6Σd²÷n(n²-1))

p=1-(6(627.25)÷n(n²-1))

p=0.86

This suggests strong positive correlation and we can therefore disregard our null hypothesis and establish that there is correlation between the temperatures of rock pools and the number of snails found there.

Our degrees of freedom value is 28.

We will use a significant level of 5%, which means the hypothesis must be accepted if the significance levels are greater. The correlation is 95% reliable, as 5% are rejected; this is the value of reliability that all scientists work from. Since our significant levels are greater than 5, we accept our hypothesis.

Conclusion

My results suggest my earlier hypothesis was accurate. There was a positive correlation between size of dog whelks and temperature. This would have been because warmer temperatures are preferred by dog whelks. As explained previously, this could be due to a number of reasons, including the temperature affecting oxygen levels, the amount of prey, the salinity of the water and the amount of water.

A secondary conclusion to make would be that the results taken on middle shore were warmer than lower shore. This would be because water on middle shore had longer to warm up. This also means that from my graphs it can be seen that higher numbers of dog whelks were recorded.

However, with a larger range of temperatures, we would have found a normal distribution, with the larger numbers favouring mid-range temperatures. In this case, I would use the T-test rather than spearman’s rank, as it is more useful at testing a normal distribution. This signifies a drastic issue with my experiment.

Evaluation

I think my experiment was fairly successful as it did provide me with the results I expected. However, there were problems, and conducting a larger scale investigation would result in more accurate and reliable data. This would involve experimenting in various different environments, although remaining on rocky shores, as that is the preferred habitat. I would try and take a bigger sample size, and obtain more accurate equipment.

Ideally, I would also do another experiment, on a different rocky shore, to see if the same things were found in different places. I would want to repeat the experiment in various weather conditions to test whether there is a normal distribution curve. By this I mean dog whelks will die in extreme hot or cold conditions.

More dog whelks were found on dry land but the temperature could not be measured, because the thermometers did not seem to measure air temperature as accurately. Also, the equipment (the ruler and thermometer) were not accurate enough. We definitely would have needed a more accurate thermometer were the experiment to be repeated.

I learned a lot from my experiment, including various aspects of safety. Unfortunately, the safety aspect of it could have affected the results, but we had to make sure we didn’t injure ourselves clambering over sharp and slippery rocks, or wading through water that was too deep.

I enjoyed this experiment as I liked monitoring living things and the way they are affected by conditions. I enjoyed working on the beach; as a site for the experiment it was good.

Bibliography

Non-web-based - The influence of water temperature on the life of the dog whelk Thais Lapillus (Gastropoda: Prosobranchia) M J Largen Department of Zoology, Queen Mary College, London. About how temperature affects the dog whelk, a study written by a professor of zoology and therefore quite reliable as his reputation would be ruined if he was wrong. Reading through it some of the information seems badly supported so I only used the bits I felt he had evidence for.

Non-web-based – Behavioural response of the dog whelk to a temperature gradient Martha Elizabeth Casterlin and William Wallace Reynolds Also about how temperature affects a dog whelk. This study seems sometimes too reliant on theory as proof of what they are trying to say and I think this shows a weakness. Some of the information however is very valid and useful to some extent.

Non-web-based – Feeding habits and zonation in some intertidal snails K Bakker This is a very useful study as it is thoroughly backed up by experiments. Whilst most information regarding feeding habits is mainly speculation, this is supported and in depth.

www.wikipedia.com – As everyone knows there is a certain amount of controversy over how useful Wikipedia is. However, this article seems to be very well structured and thought out, with lots of evidence to back up the main points.

http://www.marlin.ac.uk/biotic/browse.php?sp=4288 – This study talks about how temperature affects feeding habits. It seems well researched. It also makes good use of the information to draw valid and useful conclusions and is concise.

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