Before deciding on what to do for my main investigation, I decided to carry out a preliminary investigation on two different beaches. One was sheltered and one was an exposed beach. This preliminary investigation will give me some knowledge of the variety of species on the beaches from which I will choose one to concentrate on in my main field study.
I chose a site close to Mumbles, which is near Swansea in Wales as the site for the investigation because there is a sheltered and an exposed beach very close to one another in that area. One is exposed to the powerful waves of the Atlantic Ocean while the other is sheltered by a bay. I will also observe the changes in species abundances to give me an idea of where the different zones on the beaches are and so help me further with choosing my main investigation.
I will be using a transect technique to record my data, this way the investigation could be repeated easily as the method is simple and allows for a margin of error. There are three types of transect but I have decided to use a belt transect for the following reasons. A line transect involves recording data along the whole length of the beach, from upper shore to lower shore, which is impractical given our time limit of between five and ten hours to record our data. A point transect is the recording of specific points along the transect line, and this is impractical as it will not produce enough data for useful statistical tests or to draw sufficient conclusions from. However, a belt transect divides the line going down the beach, and readings are taken using a quadrat at equal spaces along the line.
Quadrats – A quadrat is a simple square that has a grid inside it. This grid makes it easier to accurately approximate a percentage cover within the quadrat. I found the optimum quadrat size by starting with a small quadrat, counting the cumulative number of species found in it, then replacing that quadrat with a larger one, counting the cumulative number of species found within that area and so on until the cumulative number of species stopped increasing dramatically.
I found the optimum size in this case to be 0.5m2. Other than the quadrat, the only apparatus needed was a 10m long piece of rope. I decided to take readings at ten metre intervals by the same I way I chose the size of quadrat used. I found that taking readings at longer intervals would my results too vague and that if I took the readings at shorter intervals, I would be wasting time.
During the preliminary investigation, I decided that I would only record the presence of certain known species that live under certain conditions. This way, if found I could assume that these conditions are present in the areas that these species have been found. I chose these species on the basis of the knowledge that they were present on the beaches I would be taking readings from. The ten species I recorded abundance of were:
Lichens (in general)
Fucus Ceranoides – Seaweed
Fucus Serratus – Seaweed
Fucus Vesiculosus – Seaweed
Patella Vulgata – Limpet
Barnacles (in general)
Littorina Saxatalis – Periwinkle
Littorina Littorea – Periwinkle
Littorina Littoralis – Periwinkle
Ascophyllum Nodosum – Seaweed
For species such as the various seaweeds, it is difficult to give an approximate percentage of cover and so the ACFOR scale had to be used. Between 100% – 80% was recorded as ‘Abundant’, between 80% – 60% was recorded as ‘Common’, between 60% – 40% was recorded as Fair, between 40% – 20% was recorded as ‘Occasional’ and between 20% – 0% was recorded as ‘Rare’.
However for species whose numbers could be easily counted such as the Limpets, a definite number is given and for those species such as the lichens and the barnacles, an approximation for percentage abundance was made by three individuals and the average was taken to make the estimation fair.
The data from the readings can be found in the attached appendix. When looking at the results, I took into consideration the different variables that affect the growth the different species. These variables include the amount of light, wave action, and number of people certain areas of the coast are exposed to, as well as predators, wind speed.
Main Investigation on Ascophyllum Nodosum
When carrying out the preliminary experiment, I noticed a particular type of seaweed that seemed to have air bubbles along its length. This was what first caught my attention and then upon further inspection I found that the frond length and the number of air sacs that these plants held differed up and down the coast. With this in mind I have decided to investigate what may cause these differences in frond length and number of air sacs.
I will divide the beach into two specific zones, the upper – mid zone and the lower zone. The lower zone is the area below the mid-shore point and the upper – middle zone is the area above the mid-shore point to where the splash zone ends. The mid-shore point is the line directly in the middle of the end of the splash zone at high tide, and where the water is at its lowest at low tide.
In these two areas I will take random readings at unspecified areas of the lengths of the Ascophyllum Nodosum fronds and also the number of air sacs or bladders on these fronds. I will use a thirty-centimetre ruler to measure the lengths of the fronds to the nearest centimetre and count the number of air sacs using my hands to feel for the lumps. I have decided to use a thirty-centimetre ruler for convenience as a metre rule would be too long to carry around on the rocky shore and because anything smaller would make it hard to determine an accurate length of long fronds. In the preliminary experiment, I found that the lengths of the fronds varied so greatly that taking measurements to the nearest centimetre will be sufficient to gain data that will show a variation.
I will take sixty readings for both frond length and number of air sacs from each area, giving me two hundred and forty readings in all. Anomalous readings are always inevitable, however by taking so many readings, any anomalous values that will be recorded will make little difference to my final statistical data and so will not affect my conclusions.
Through research on the Internet, I have discovered that the Ascophyllum Nodosum plants do not begin to grow air sacs until their fifth year and then only grow one each year after reaching that stage of maturity and so the age of the plant can be determined by knowing the number of air sacs on one of its fronds. However, this can also be misleading due to the fact that fronds can be torn off by rough conditions such as constant wave action and so an accurate age of the plants cannot always be established.
In this case, the apparatus is not hazardous, but the environment in which I will be carrying the investigation will be. I will be taking readings from rocky beaches and to avoid harming myself by slipping on the wet rocks, I must pay attention to where I step. As a safety precaution I will be near at least two other individuals at any given time, so if I do happen to fall, help will not be far away. This will work mutually as I will also help either of the other two if they happen to fall. Common sense will be key to safety. Also wearing sensibly clothing will help. I will wear shoes with a good tread that has not worn away to help avoid slipping on the wet rocks.
I believe that the frond lengths and number of air sacs will be lower, below the mid-shore line than those above the mid-shore line. This may perhaps be due to the fact that the plants above the mid-shore line will be exposed to sunlight longer than those plants below the mid-shore line, which are submerged by water longer.
The method I used was the same as I had planned. I managed to not fall and hurt myself and I thank the safety precautions I had planned for this. I found that the wet rocks were very slippery and at times it was difficult to avoid tripping.
The data I collected can be found in the attached appendix. Before carrying out the Student’s T test I had to first confirm that I had a wide enough range of readings by comparing the running averages against the actual readings. I plotted these points on a graph to see if my running averages made a fairly level horizontal line, which would prove I had a natural distribution. The data used to produce the graphs below can be found in the appendix.
These graphs show that the running averages level off nicely and so I know that there is a fair distribution of results from both sets of readings. Now I know that there is a good distribution, I can carry out the Student’s T test to see if I can confidently conclude whether or not there is a distinct change in the average frond length in the two different areas. The Student’s T test takes anomalous points into consideration and the result of the test gives you a definite probability of whether chance alone could cause the difference in frond lengths rather than there being a significant reason.
I found my T value for the frond lengths to be 12.34 (2dp), which is much higher than the critical value of 1.66 at 118 degrees of freedom. This shows that I can be 95% sure that the differences in the two sets of readings are not due to chance, but because of differences in the plants environments.
I found my T value for the number of air sacs to be 5.67 (2dp), which again is much higher than the critical value of 1.66 and again shows that that I can be 95% sure that the differences in the two sets of readings are not due to chance, but because of differences in the plants environments.
My results show a definite difference between the frond lengths and number of air sacs between the zones above and below the mid-shore point. They show that below the mid-shore point, the frond lengths and the number of air sacs on each frond are significantly lower than above the mid-shore point. This disproves my hypothesis, which stated that the overriding factor would be the exposure to wave action.
There are many factors affecting the growth of the Ascophyllum Nodosum plant, and now in hindsight I can look back and logically explain why the wave action would not be the deciding factor of frond length and number of air sacs on each frond. The main reason for this would be that I did the investigation on the sheltered beach, and so the wave action would not be harsh enough to tear the fronds off the plants and therefore would not be a limiting factor to the growth of the plants. With this in mind I can now try to understand which factors would be key.
Growth of the plant can only occur in the presence of light, as photosynthesis must happen for any growth to take place. The area below the mid-shore point is submerged by water almost twice as much as the area above the mid-shore point. This means that the Ascophyllum Nodosum plants which are rooted below the mid-shore point have around half as much time as the plants which are rooted above the mid-shore point in which to photosynthesise during the hours of light. This would mean that the growth rate of the plants in the middle to upper zone would be much higher than the plants in the middle to lower zone.
Through research I have found that it normally takes five years for the Ascophyllum Nodosum plant to reach maturity and only then does it begin to produce air sacs and reproduce. If the conditions are unfit, then the time taken to reach maturity can increase and so even though the plants on the beach may be of the same age, they can have different numbers of air sacs.
Desiccation can also be a limiting factor in the growth of the plants. If it were a major factor, then I would have found that the plants above the mid-shore point would also have short frond lengths and a low number of air sacs. However, this was not the case, and this can be explained by the fact that the productivity of the plants is only affected if water loss exceeds 50% as Bruinkhuis discovered.