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Blackfly larvae

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Contents Page Page One --> Aim Hypothesis Research and Rationale Method Page Two --> Apparatus list and Justifications Page Three --> Pictures of apparatus Explanations of investigation technique Page Four --> Controls Ethical Considerations Page Five --> Pilot Study Page Six --> Safety Considerations and Risk Assessment Page Seven --> Raw Data Tables Page Eight --> Graphs showing correlation Pages Nine, Ten & Eleven --> Spearman Rank Correlation Test Page Twelve --> Evaluation Bibliography Aim In this coursework, I will investigate how depth affects the density of simuliidae (blackfly) larvae along the transect of a river. Hypothesis I hypothesise that in deeper transects of the River Conwy, there will be a lower density of simuliidae larvae. Null hypothesis - There will be no correlation between the data that I find. Research & Rationale The larvae and pupae are aquatic but are confined to shallow, running waters where they attach themselves to firm, usually smooth, substrates. The outlets of ponds and lakes are particularly favoured and productive habitats [1]. When carrying out a preliminary investigation in the river, I noticed that there was an abundance of blackfly larvae in the faster streams of water. As this was the only transect of the river that I took measurements from, it raised a curiosity, in which I wanted to know whether they preferred these conditions. After conducting some research, I found information which suggested that the larvae preferred fast flowing water, but much less on how the depth of water affected their abundance. Larvae selected areas with suitable water velocities and aligned with the flow, providing flow visualization of micro-current speed and direction [2]. Different types of larvae prefer different conditions and I want to establish and prove the habitats that the simuliidae larvae prefer, with my investigation. The larvae have no true legs, though in some, small swellings under the body serve as legs. Antennae, with one to six joints, are usually inconspicuous I have decided to carry out my investigation in the River Conwy, Wales, as there was an abundance of the species when I tested it previously. ...read more.


Once I have counted them and double checked the number of blackfly larvae in the tray, I will pour the contents of the tray straight back into the river, so that they can quickly find a new habitat to live in. I hope not to disturb them too much, and will make sure that I take their requirements (as living creatures) in consideration. I now have enough information to carry out a pilot study, where I will test my method and then make any adjustments that are necessary. Word Count - 1360 Pilot Study I began in a pool of water that was mainly above 20cm deep, to discover how long I would need to do the kicking technique for. I will choose a random co-ordinate and assess the different options that I have. Length of time /seconds Black fly larvae in test one Blackfly larvae in test two 30 60 90 120 1 5 4 2 0 6 5 4 There is a fractional advantage to using the technique for 60 seconds, so I will alter the amount of time that I do the kicking sample for. For the next test, I went to the following points to receive data: 12cm (both of which were selected randomly) 18cm As I need to find out the number of repeats that are necessary in my investigation, I will carry out a trial, for 60 seconds, at the two co-ordinates specified earlier, and I will use a running mean so that I am as accurate as possible. 12cm for 1 minute 1 3 1.67 1 2.5 2.4 5 2.4 2 0 This running mean shows that three repeats are likely to find me the most reliable results. 18cm for 1 minute 1 1 0.67 0 0.5 0.6 0 0.5 1 0 This confirms that I will carry out 3 repeats on each co-ordinate. I have also decided from this pilot stuffy that the area I was investigating was not giving me substantial data that I could ...read more.


Evaluation In my pilot study, I noticed that when I tried to carry out my investigation in the deeper pools of the River Conwy, there were very small numbers of blackfly larvae that I was finding. It was very difficult for me to see a correlation, because it was quite rare foe me to actually find any blackfly larvae. Eventually, once I had moved from the pools, into areas of varying velocity and depth, I found a much wider range of values, upon which I could base my investigation on. Typically, the larvae of the black fly can be found in and around aquatic habitats such as fast and slow flowing streams, shallow ponds or standing water sources during certain times of the year. The larvae attach to various substrates in the aquatic habitat such as logs and rocks where after a period of time, they pupate and eventually hatch [3]. My choices of method were definitely advantageous to the investigation I was carrying out, and I think that the equipment was also of the best quality, and use to me. Current published theories state that blackfly larvae do prefer to live in shallow fast flowing water, and yet my experiment clearly shows that this may not be the case. Some of the deeper areas that I measured were also quite fast flowing, so I think it is the velocity/speed of the water that the larvae are attracted to, and not actually the depth. When I tested still deep water, there seemed to very few larvae there. The validity of conclusions is dependent on the experimental method used and the quality of the results obtained. My investigation proved that the black fly larvae do tend to prefer deeper, but fast moving rivers. I haven't yet found out why, but perhaps if I were to do a similar experiment again, I could examine the difference between deep and shallow areas, and see whether there was any new information gathered in these. ...read more.

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