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Seaweed Desiccation

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When looking out onto the beach, there are various sections that are visibly different from one another. These zones are due to seaweed, the size, density and more obviously colours. The most common colour seaweeds are browns, from the phaeophycae family. During the day, as tides come and go, the seaweed becomes saturated and then starts to dry out, called desiccation.

This coursework will look at the adaptations of seaweed?s to reduce desiccation, and also the factors that cause the desiccation of seaweed. To begin with, the actual method will have to be looked at to determine a good way of retrieving the data, and then how to interpret the results to produce useful data.

The seaweeds I will be looking for to test will be brown algae (phaeophyta), in particular, I will be looking for seaweed?s from all areas of the shore, starting by the waters edge and moving to the areas of high tide, the furthest extreme from the waters edge.


Channel Wrack: Channel wrack is found at the high water mark. This is a small seaweed, about 10-15 cm in length. It has a distinct channel running down one side of the frond. It is held onto the rocks by it?s holdfast to prevent it being washed away during high tide. Channel wrack spends about 70-90% of the time out of water, due to the fact that it lies above the high water mark of neap tides.

Spiral wrack: In the zone below the channel wrack, spiral wrack grows to be between 12-35 cm in length and is uncovered for about 60-70% of its life. The fronds of the spiral wrack are broader and flatter than those of the channel wrack, and have a distinctive mid rib as opposed to a channel or groove. The fronds are twisted into a spiral, hence the name.

Knotted wrack/Egg wrack: This seaweed covers a large amount of the beach, and can grow to be up to 2 metres in length. The top part of this section can be out of the water for about 55% of its life, while some of the bottom seaweed can be out of the water for just 15% of its life. The knotted wrack has ?bubbles? all along its fronds, which act as buoys to keep the seaweed in the sunlight whilst it is submerged.

Bladder wrack: This seaweed can grow to be about 1 metre long, and exists alongside the egg wrack. It too has bladders of gas along its fronds, which help to separate the fronds when in the water, and therefore allowing all parts of the plant to photosynthesise. The fronds are broad and flattened, and possess a mid rib.

Serrated wrack: This species generally grows to be about 60cm long, and spends most of its life submerged in the zone below the egg and bladder wrack. This zone is exposed at low water during spring tides.

Oarweed/Laminaria saccharina: Sub-tidal. Large brown algae rarely out of water except at low tide. Large fronds, and holdfasts ?sticking? the seaweed to rocks below the water. Mucilaginous to help retard water loss. Fronds are thick, with a large surface area.

Amongst the seaweeds I will be using, there will also be examples of green and red algae as well as small animals. I will be careful not to disturb the habitat, and so not unbalance the ecosystem. This will be taken into account at all times during the investigation, and all of the seaweeds will be returned to the beach after the practical to provide habitat and food for any other organisms.

PLAN: I will collect small amounts of each of the above seaweeds as my sample. The seaweeds will be taken from along a single transect to reduce the number of discrepancies in my final results. I will also only use seaweeds that are normally found in that zone, as this will reduce the number of seaweeds being used that could have been washed away from their actual position, and therefore already be dead which would affect my results. The seaweeds will then be placed in a bucket of seawater to reduce any desiccation prior to the experiment. I will need to use seaweeds from all over the beach to allow me to obtain results showing adaptations against desiccation, if there are any. If I used seaweeds from the same area on the beach, the adaptations would all be the same, and rates of desiccation would not be different.

The seaweeds will be kept in the bucket of seawater for 24 hours to allow saturation. To actually carry out the process of testing desiccation, I will prepare a line to hang the seaweeds off. The seaweeds will then be weighed, and hung on the line. The weighing will allow the results to be used to see how much water has been lost from the seaweed during a set time period. The seaweed will be spread out along the line however so that water molecules from one seaweed does not diffuse into the one next to it. I will use paperclips, shaped as hooks to hang the seaweeds with as I feel these would be the best things to use to restrict the damage done to the seaweeds.

The seaweed will not need to be a certain weight to begin with, as it is the percentage water loss that will show the desiccation rates, from which various graphs can be drawn to show comparisons between the seaweeds. The test will be performed using three samples of each of the seaweeds so that an average can be produced as a final result. To hang the oar weed, I will need to cut it down so that it is a suitable size for on the line. To reduce any water loss through cutting I will seal the edges with petroleum jelly, although I will acknowledge that this could give an unfair advantage to the oarweed in staying saturated. (The other seaweeds will not need to be cut and therefore will not have the extra sealing agent around the fronds.) Throughout the experiment I will need to ensure that some variables are standardised. The temperature of the room will be the same for all of the seaweeds, as will the light. This means that although the light and temperature may change throughout the day, the actual seaweeds will all have experienced the same conditions. The length of time in the bucket of seaweed and the times between recordings of masses will also be the same. This is to try and reduce any anomalous results, and also to ensure that the results are as close to being a true representation of desiccation as it would be on the beach.

The mass of the seaweeds will be taken at various intervals during the day, although at night it will be difficult to take the results. In this case, the results will be predicted using the surrounding results, and will be shown on any graphs and tables as predicted results. Again this could lead to discrepancies in my final results, and this will have to be addressed. The last result will be taken when changes in weight have almost reached a constant mass. However there is a chance that the experiment will not have stopped by this point, so again this will be referred to in my conclusions, if any problems do arise. Also, throughout the experiment, it will be assumed that loss of weight is loss of water, another point that will need to be addressed in my conclusion.

DIAGRAM METHOD: 1. Collect 7 sorts of brown seaweed from shore , and transport to lab in a bucket of seawater.

2. Leave the seaweeds in the bucket of water for 24 hours to ensure saturation.

3. Record the mass of each seaweed.

4. Hang seaweeds onto line (see diagram) 5. Record the masses at various intervals during the day, ensuring that all seaweeds are weighed, and the scales are set at 0 for each measurement 6. Try to keep light and temperature as constant as possible, and ensure that all seaweeds are kept in the same conditions for the duration I believe that my results will show that seaweeds from different zones on the shore do have adaptations that reduce the rate of desiccation. This is due to the varying times that the seaweeds are left out of the water when they are on the shore. The difference in surface area:volume will also have an effect on the results. Ficks Law will become important here in assessing the relation between surface area, volume and water loss.

ALTERNATIVE HYPOTHESIS: Seaweeds nearer to the water?s edge will have a faster desiccation rate than those further up the beach.

NULL HYPOTHESIS: There will be no correlation between distance up the beach and desiccation rate.

Once my results have been collected, I will produce a table showing the masses of each seaweed samples, the averages and the times that the weights were measured. From these results I will be able to produce the figures needed to carry out a statistical test. I will use Spearmans Rho as this will show whether my alternative hypothesis was correct or not. Spearmans Rho shows correlation between results, so will be useful in drawing conclusions about whether or not distance from watermark is an important factor in desiccation.

Throughout the experiment I will need to observe various safety aspects. For instance, on the shore I will need to ensure that I wear suitable clothing and footwear. For example, walking boots will allow improved grip on the rocks, which will be slippery due to the seaweeds living on them, and will also offer support to my ankles if I do slip. Safety for the organisms will also need to be observed. In this case, any rocks moved will be replaced in the exact place, whilst observing any animals or plants that may become injured when the rock is returned. All organisms and/or other things removed from the beach will be returned at the end of the field trip. In the lab, extra care will be taken when moving around the lab, due to the wet conditions that will arise from working with seawater. When cutting the seaweed, care will be taken with the knife and also hands will be washed regularly to stop any seawater being consumed which could cause illness.

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