Adult freshwater shrimps

This project was carried out to compare the number of adult and juvenile freshwater shrimps at the edge and the middle of the river Mole in southern England. Twenty kick samples were carried out, with 10 at the edge and 10 in the middle. The results showed that there were more juveniles at the edge and more adults in the middle where the flow rate was higher.

Hypothesis

The number of adult freshwater shrimps will be greater in the middle of the river, and more juveniles at the edge of the river. The flow rate will be greater in the middle than at the edge.

Research and Rational

Freshwater shrimps are transparent, with a thin outer shell that is shed in cycles. They have a large spine, ten legs, are excellent swimmers and have a body that is flattened sideways [6]. Their legs circulate fresh, oxygen rich water over their gills [7].The results of this investigation can be used to give an idea of the adaptations of similar freshwater invertebrates with similar characteristics.

Unpolluted water contains stonefly and mayfly nymphs, freshwater shrimps and caddis fly larvae. Freshwater shrimps are intolerant of polluted waters, as it can damage the delicate gills which they use to breathe and can therefore be used as an indicator species for the quality of water [6][1]. This means that freshwater shrimp can be used to measure pollution by using the Biotic Index. Biotic index is a scale for measuring the quality of an environment by indicating the types of organisms present in it. It can show that certain species tend to disappear and the species diversity decreases as pollution in water increases. It is measured on a scale of 1 to 10 where organisms intolerant to pollution have a higher number. Pollution may be different at the edge compared to the middle; therefore it might affect the results [2].

Eutrophication is a process in which an ecosystem accumulates mineral nutrients. It is usually linked with human activity that releases nutrients into the environment. Excess fertilisers used in farming can move into rivers, releasing nutrients. This can lead to explosive growth of algal. Biomass produced, excludes light from the water and results in the deoxygenating of the water, killing invertebrates [3].

"Young freshwater shrimps are small enough to be eagerly accepted by most fish" [5]. According to this quote, juvenile freshwater shrimps are a food source for fishes, which is why they should be conserved. This can mean that there will be more adults in the river; as fishes will eat more of the juveniles. People who keep fishes as pets should know about which part of the river (edge or middle) to look in, to find juvenile freshwater shrimps.

Trout is a water bird which lives on tiny creatures found at the water's edge, which may affect my results. The experiment will be carried out in September, which is the trout fly fishing season. 40% of their feeding consists of freshwater shrimps during this season [4]. The results from the investigation can be used to indicate the health of the ecosystem by looking at how freshwater shrimps support the primary and secondary consumers.

Planning

A trial experiment will be carried out to see how effective my method is. I will use systematic sampling and will take twenty samples. Ten samples will be taken at the edge and middle. I will take ten samples to get reliable results.

My independent variable is in which part of the river I will take my sample (middle or edge). Flow rate will be measured using a hydro prop flow meter and will be measured in ms-1. To set up the hydro prop I will attach the impellor to the hydro prop stand and place against the flow of the water. The rate will be measured before each of the 20 samples, where I will perform the kick samples. I will use a stopwatch to see how long it takes for the impellor to reach the end. A stopwatch will give me more accurate results and reduces the risk of human errors. Before I start my kick samples I will also measure the pH and temperature using a temperature probe which measures both pH and temperature. It is important I measure both of these variables as they may affect the results. To set up the temperature probe I will place the probe in the water to collaborate and wait for the results to show up. Both variables will be measured before each of the 20 kick samples and the temperature will be measured in oc. It will also be important to measure the concentration of oxygen, as it may affect the results. It will be measured in mgl-1 using an oxygen meter, which will have to be collaborated using the instructions provided. Oxygen will be measured before each of the 20 kick samples. Next, I will place the D frame standard net up right making sure the water flows in. A stopwatch will be used to time my kick samples to 25 seconds. Once the kick sample is complete, I will transfer all of the invertebrates collected into a tray filled with water. Using a pipette, I will transfer all the freshwater shrimps into a pot filled with water and count the numbers of juvenile and adults, which is my dependent variable. I will then empty out the tray and repeat these steps again.

It will be very difficult for me to control some variables but it is possible to reduce their effect on my results. I will carry out and complete the experiment on the same day, as it will be likely that the oxygen concentration, pH level and temperature will not have changed drastically in that time
Mann Whitney U Test is going to be used to analyse the data, which will compare the median of the data for:

1) The flow rate of the river in the middle and at the edge.

2) The number of adult freshwater shrimps in the middle and at the edge of the river.

3) The number of juvenile freshwater shrimps in the middle and at the edge of the river.

The trial results from table 2 suggest that there are more juveniles at the edge and more adults in the middle. Sample 3 at the edge is an anomalous result, as no juveniles were found. The results cannot be seen as reliable, as more repeats are needed. So far the results show that the temperature, pH and oxygen levels do not affect the number of freshwater shrimps.

Modifications

I could only complete 6 out of the 20 trials because I spent too much time looking for the freshwater shrimps in the tray. Therefore, I have now decided to spend no more than five minutes each time I carry out this step. I have also decided to apply an elastic band around the point at which the flow meter is inserted into the stream, so in each sample the same depth of the flow meter is inserted. I have also realised that light intensity may also affect my results but I do not have a light meter available, therefore I will try to reduce the effect by completing the investigation before light fades so most of the results are taken near enough in the same light intensity. The stream I was using had lots of areas which were shaded by trees, so I have decided to change my spot to a place where there are fewer trees.

Ethical issues

It is possible that invertebrates died or got injured during kick sampling. This is why I will let the invertebrates back into the river after recording my samples.

Conclusion of results

It is clear that the flow rate does have an effect on freshwater shrimps. The number of adults is more in the middle with a total of 127 but is not a great deal higher than the total of 118 at the edge. The table suggests that there are more juveniles at the edge and less in the middle with 75 more juveniles at the edge. It seems that oxygen, temperature and pH have not affected the number of freshwater shrimps.

It seems that juveniles prefer the edge as they are more likely to be eaten by fish in the middle. The results show that there are more adults than juveniles in the river. "Parasite-induced changes in behaviour and colour make a freshwater shrimp more prone to fish predation" [9]. This may be a reason why there are fewer juveniles, as they will be less able to protect themselves like the adults do, therefore more juveniles get eaten. Research by J.Quirt and D.Lasenby has shown that adult freshwater shrimps can sometimes eat juvenile freshwater shrimps which can also affect the total number of juveniles [10]. Freshwater shrimps have the adaptations making them more suited to slow flowing water [6]. Adult freshwater shrimps can survive in fast flowing water, which is why they are everywhere [1]. It looks as if juveniles are not physically capable to cope with fast flowing streams at a young age.

Analysis of tests

Test 1 showed that there are more juveniles at the edge compared to the middle, because at the 5% probability level, the smaller U value of 5.5 was lower than the critical value of 23. Thus, there is more than 95% chance that the results are significantly different. This supports the experimental hypothesis that there is a significant difference in the number of juvenile freshwater shrimps in the river at the edge and the middle.

Test 2 showed that there is not much difference between adults at the edge compared to the middle. This is because at the 5% probability level, the smaller U value of 41.5 was larger than the critical value. Consequently, there is more than a 95% chance that the results are not significantly different. This supports the null hypothesis that there is no significant difference in the number of adult freshwater shrimps in the middle and edge.

Test 3 showed that the flow rate is greater in the middle compared to the edge, because at the 5% probability level, the smaller U value was lower than the critical value. Therefore, there is more than a 95% chance that the results are significantly different. This supports the experimental hypothesis that there is a significant difference in the flow rate at the edge and the in the middle.

Evaluation

I have realised that no matter how carefully I carry out this investigation, it will be difficult to keep account of all the factors which will cause variations. The number of stones under water could have been a limiting factor, since freshwater shrimps are normally found under stones [6]. It was not possible for me to find a section of the river where the stones were even in the middle and edge. To reduce the effect of stones, I should have noted down if I thought a sample position was stony, less stony or not stony at all. Further research should be carried to see how stony rivers affect the number of freshwater shrimps. It was possible that I did not count some of the freshwater shrimps, as I was following a strict 5 minute rule. If this investigation was done in a group then it would have been possible to spend more time counting. I carried out 20 kick samples for 25 seconds. I noticed that the number of kicks for each sample was different. I should have set up a rule, such as one kick per second for 25 seconds. Pollution level could have been different at the edge and in the middle, affecting the results. A procedure could have been used to find the Biotic Index score for samples of freshwater invertebrates.

From table 3, the tenth oxygen reading in the middle is anomalous which could have been a systematic error. I had some problems collaborating the oxygen meter, as the instructions provided were not clear. The third reading of the flow rate in the middle is also anomalous and could have been caused by me not inserting the flow meter at the point of the elastic band.

Source 1 was a well known book, when it was first published. It was published in the year 2000, so may be out of date. Source 2 is a worksheet directed at students, so must have been proofread for errors. Source 6 is a booklet written by the NSW Water Bug Survey who check the health of rivers. Schools use the survey for educational purposes, so this source can be relied on. Source 3 is from a university in the UK. Source 4, 5 and 8 are websites which contain many articles written by experienced researchers. Source 10 is NRC Research Press and is one of the most advanced publishing services. Source 11 is a website which collects photographs of Great Britain. Source 7 is a journal and has been released annually since 1932. I would not regard this source as reliable; as the volume I used is from 1974. Source 9 is a journal which publishes research conducted by experts. This source can be regarded as reliable.

Bibliography

1. Pollock S. (2005) Eyewitness Ecology. New York, United States: Dorling Kindersley Publishing, Inc.

2. Unknown author (2008), Estimating environmental damage in fresh water, Advanced applied science: GCE A2 UNITS, The Nuffield Foundation, 1-2

3. The Open University (date not available). Science and nature. http://openlearn.open.ac.uk/mod/resource/view.php?id=171975 [Accessed on 26 November 2009]

4. Fishing in British Columbia (date not available). Article by Ron Newman. http://www.bcadventure.com/adventure/angling/bugs/shrimp/shrimp.phtml [Last accessed on 24 November 2009]

5. Torrens family (2008). Natural history: Fresh water shrimps. http://www.torrens.org.uk/NatHist/Aqua/Gammarus.html [Last accessed on 24 November 2009]

6. Unknown author (date not available), Fresh water shrimp, NSW Water Bug Survey: Buglopedia Index, p.17

7. Martin A.W. (1974) Circulation in Invertebrates. Annual Review of Physiology, 36(n/a), 171-186

8. Teifi Rivers Invertebrate Monitors (2009). Gammarus Pulex. http://www.riverfly.co.uk/interesting.htm [last accessed on 26 November 2009]

9. Theo C. Bakker, Dominique Mazzi, Sarah Zala (1997), Parasite-induced changes in behaviour and colour make Gammarus pulex more prone to fish predation, Ecology

10. Canadian journal of zoology (2009). Freshwater shrimp: Mysis relicta. http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?journal=cjz&volume=80&year=&issue=&msno=z02-084&calyLang=eng [Last accessed 22 November 2009]

11. Geograph British Isles. Stepping Stones. http://www.geograph.org.uk/photo/158891 [Last accessed 20 November 2009]

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