Blackfly larvae

Word count - 534

Once I have gathered all of my data, I will take use a statistical test. As this is a correlation investigation, the most ideal test would be the Spearman Rank. It is a technique that tests the direction and strength of the relationship between two variables.

Apparatus list and justifications

To carry out my investigation, I will need the following apparatus:

                                                                   

                           

                                                                 

This is the quadrat that I will use to keep the area that I sample constant. I will always place this in the river before I sample, and then carry out the kicking technique inside the quadrat.

     

                                   

Word Count - 809

  This is an example pf the kick sampling technique that I will be using. I will place the net in the river, and then kick the stones, to unsettle the blackfly larvae so that they float into my net.

             

 

                         

This is the FBA approved net that I will use to catch the blackfky larvae. As the larvae are small, the net will need to be small and suited to the size of organisms, so that I can catch them with the equipment available

In this picture, I was sorting through the water in my bucket, in preparation of pouring the contents of the bucket into the tray for closer inspection.

Here, I was standing on the side of my quadrat to ensure that it didn’t float too far downstream. I was about to move onto the other side of the quadrat so begin the kicking technique to dislodge the organisms.

Word Count - 967

Controls

Keeping all of my variables the same will ensure that I have a reliable experiment, and that no other external factors will affect my results. My dependent variable will need to change, as this is key to proving my hypothesis to be true or false.

Ethical considerations

I will also need to take into account the treatment of the blackfly larvae as I count the abundance of their species. It is important that I am ethically considerate, so I will need to take some precautions into account, to ensure that no blackfly larvae are harmed as I carry out my investigation. I will ensure that when I collect the organisms in the net, I will put them into a bucket of river water, so that their temporary habitats is similar to their permanent one in the river bed. I will also try o count them as quickly as possible, and I won’t use any instruments that may harm them as I count them. 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.

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 find a correlation from, so I decided to move my data from a pool, into a an are of mixed depths and velocities. I will measure in a deep area, a medium area, and the most shallow area of the river, so that there is variation. I think that there is a denser population of blackfly in riffles.

Word Count - 1668

Safety Considerations and Risk Assessment

I will undertake all of the above safety precautions so that I do not suffer from any avoidable injuries or incidents whilst carrying out my investigation in the river.

Word Count - 1779

Results

Raw data table:

From this data, there doesn’t look like there is a significant correlation, but I will need to put the information into a graph and then use a statistical test to scientifically test whether there is a correlation between the depth of the river and the abundance of the blackfly larvae.

Word Count - 1996

This graph shows a generally positive correlation, and while there are a few anomalies, it is clear that in the deeper parts of the river, there were more blackfly larvae.

This graph shows a similar correlation; the deeper areas of the river have a larger population of blackfly larvae. The anomalies still show a positive correlation.

There is a much weaker correlation in this graph, and from this graph alone, it would seem as though there is no connection between the depth of the river, and the abundance of blackfly larvae.

Word Count - 2087

Spearman Rank Co-efficiency Correlation Test

I will now carry out a statistical test to see whether I can accept or reject my hypothesis. If the values that I get are lower than the critical values within that range of pairs, I will have to reject my hypothesis and accept my null hypothesis. If the value is equal to, or higher than the critical value, I can accept my hypothesis.

This is the spearman rank correlation for the deepest line in the river

      Rs = 1 – 6 (Sum of D squared)

                         n ( n squared -1)

            = 1 – 6 (210)

                     15 (225-1)

            = 0.625                  

Critical value = 0.544.

Word Count - 2299

Spearman rank correlation for the middle line in the river

      Rs = 1 – 6 (Sum of D squared)

                         n ( n squared -1)

            = 1 – 6 (176.5)

                     15 (225-1)

            = 0.685

Critical value = 0.544.

Word Count - 2439

Spearman rank correlation for the shallow line in the river

      Rs = 1 – 6 (Sum of D squared)

                         n ( n squared -1)

            = 1 – 6 (163)

                     15 (225-1)

            = 0.709    

                                                   

Critical value = 0.544.

Word Count - 2579

 

The values that I obtained for all three parts of the river were above the critical value for the amount of data that I selected, which allows me to accept my hypothesis, and reject my null hypothesis. The chance that there isn’t a correlation between the depth of the River Conwy and the abundance of blackfly larvae is less than one in one hundred.

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.

Bibliography

I used the following sources of information in my coursework:

[1] Journal of the North American Benthological Society

[2] Journal - Hydrobiologia 

[3]

Final Word Count - 2998