Algae Of The Upper Shore Rock Pool example essay topic

Comparisons of Upper and Lower Shore Rock Pools In the following study, rock pools from the upper and lower shore of Bracelet Bay, were examined and the organisms within noted. The contents of the two pools were compared. The abiotic variations of the pools were recorded and examined in an attempt to understand why the contents of the pools differed. A greater abundance and variety of organisms was present in the lower shore rock pool, this was due to the lower rock pool being a more benign environment than that of the upper shore. This was related to the exposure time of the two pools. The rock pool of the upper shore was exposed for longer and therefore suffered greater from variation of abiotic factors, as a result, the organisms of the upper pool had to possess special adaptations to coloni se the area.

The lower rock pool generally contained different species which could out compete the organisms of the upper pool when in a more benign environment. The rock pools studied should both contain organisms specially adapted to live in the intertidal environment of the rock pools. The organisms need to be adapted to the micro environment of the rock pool, as conditions are considerably different to those of a 'normal' marine environment. The rock pools spend some of their time completely submerged by the sea and other times exposed to the air. When exposed the organisms of the rock pool are part of a much smaller body of water than normal. This smaller volume of exposed water is likely to be changed significantly, mostly as a result of heating by the sun (Brehaut, 1982).

Heating of exposed rock pools mean that the organisms within have to cope with considerable abiotic variations There are three major factors which fluctuate in rock pools: 1. Temperature- this changes as a small body of water changes temperature quickly. Temperature also changes due to flooding by waves of different temperatures; 2. Salinity- this increase due to evaporation and decreases if the pool is diluted by freshwater e.g. rain. Salinity also changes like temperature, through flooding by the sea. 3.

Oxygen- this decreases with increased temperature and can also come in short supply if the pool is crowded (more of a problem at night when plant life respires as well), (Nybakken, 1988). As well as the above, carbon dioxide and pH vary. Carbon dioxide increases usually as a by-product of respiration, leading to a decrease in pH. Hence the organisms found in the rock pool should be able to tolerate changes in O 2, CO 2, temperature, pH and salinity. Such organisms include Balanus, Actinia, Patella, and Littorina who are all able to reduce their metabolic rate when the rock pools are exposed and so conserve limited oxygen, (Brehaut, 1982). Because of the changing salinity, the organisms should also be able to maintain a suitable osmotic potential even if the pH is far from optimal.

Such organisms include Carcinus maen us which can increase water loss at low salinity (Brehaut, 1982). The lower shore is not exposed for as long as the upper. As a direct result of this, all the above factors change to a greater degree in the upper shore. Temperature reaches greater extremes of both high and low as does pH.

Naturally, desiccation is also a greater problem in the upper shore. Because of this, the upper shore can be considered a significantly harsher environment than the lower shore. Hence, even more specialization would be needed for organisms in the upper shore, i.e. they should be even more tolerant. Also, because the conditions of the upper shore are harsher, there should be fewer numbers of organisms and less diversity, (Brehaut, 1982). As the rock pools are wave-beaten, the organisms within them have to attach themselves to the rocks. Such mechanisms include strong attachment e.g. algal holdfasts, cementation e.g. barnacles and adhesive feet e.g. gastropods such as limpets.

METHOD: One rock pool from the upper shore and lower shore were chosen. The physical features of the rock pools were recorded. The shape of the pools were drawn, the surface area of the rock pools worked out by measuring the dimensions of the rock pool with a metre rule and string. Pool volume was calculated using the measurements for the pool depth and surface area. Abiotic factors were recorded: -pH was recorded using a pH meter, which was calibrated before use; salinity was recorded using a conductivity meter, the reading from which was converted to salinity, (parts per thousand), using a conversion chart; oxygen levels were recorded using an oxygen meter; temperature at the waters surface and 20 cms below the surface was recorded using a thermometer. The measurements for oxygen, salinity, and pH, were repeated for the upper shore at the end of the study.

Using identification sheets, the organisms present in the rock pools were identified. The position of each organism was noted on a map of the rock pool, with each species being represented by a different symbol. The relative abundance of each species was worked out using the numbers recorded and a relative abundance key. RESULTS: Species present in the upper rock pool and their relative abundance; -Enteromorpha intestinal is- Fucus serratus- +Ulva - +Patella depress a- +Patella vulgate- +Littorina litt orea- ++Gibbula cineraria- +Carcinus maen us- +Species present in the lower rock pool and their relative abundance: -Coralline officinal is- +Ahnfeltia plica ta- +Fucus serratus- +Ulva - +Gibbula umbilical is- +Nucella umbilical is- +Littorina litt orea- +KEY: abundant, ++ common, + present. Abiotic data for the upper rock pool: -1st Recording Temperature at surface - 24.2 OCTemperature 20 cm below surface - 22.0 OCSalinity - 28 p. p/1000 pH -9.1602 concentration - 153%2nd Recording Temperature at surface - 24.5 OCTemperature 20 cm below surface - 22.1 OCSalinity - 32 p. p/1000 pH - 9.10 O 2 concentration - 140.6%Abiotic data for the lower rock pool: -Temperature at surface - 24.3 OCTemperature 10 cm below surface - 23.6 OCSalinity - 29 p. p/1000 pH - 9.11 O 2 concentration - 249.6%DISCUSSION: Results showed variation in the type and abundance of organisms found in the rock pools of the upper and lower shore. One of the most striking differences in the rock pools' contents is the dominant algae.

Enteromorpha was clearly the presiding algae of the upper shore rock pool, yet it didn't feature at all in the lower shore rock pool. The main reason for this, is that Enteromorpha is better adapted to the conditions found in the upper shore rock pool than the other sea weeds. The importance of these adaptations is amplified by the large contrast between the conditions of the upper and lower shore. Inhabitants of the upper shore have to be able to cope with the considerable variation in abiotic factors.

Such variations generally occur to a much lesser extent on the lower shore. One feature of rock pools which has increasing variance as you move up the shore, is salinity. This change in salinity, is related to the length of time the pools are sub tidal and therefore exposed to the elements. As a result of exposure the pools can lose water through evaporation, resulting in an increase in salinity. Conversely, introduction of freshwater from rainfall or run-off, will decrease the salinity, (Raffaelli and Hawkins, 1996). This was reflected by the results from the study, with the salinity of the upper rock pool at the end of the study being 3% greater than that of the lower rock pool.

This suggests then, that one possible reason for Enteromorpha's success in the upper shore is that it is able to tolerate significantly larger fluctuations in salinity than most other algae. This conclusion is backed up by experiments where Enteromorpha has been subjected to rapid transfer from normal, to diluted seawater. The Enteromorpha experimented on showed no increase in metabolic rate. Further experiments with Enteromorpha and increasingly variable salinity also showed no increase in metabolic rate. In fact, it is thought that Enteromorpha cells are extremely efficient at controlling their osmotic pressure, (Boney, 1969). It would be wrong though, to state categorically that the sole reason for Enteromorpha's dominance of the upper shore rock pool was due to it being better suited to coping with greater variance in salinity.

After all, Fucus serratus, Ulva and others, are only slightly less efficient in maintaining osmotic balance. So what other factors are of the upper shore rock pool may lead to Enteromorpha being able to "out perform" the other seaweed? Well, due to the previously mentioned increase in exposure to the elements, another important abiotic factor comes into play - temperature. Being a vast volume of water, the sea maintains a relatively uniform temperature.

However, rock pools are comparatively tiny volumes of water. Hence, when exposed, temperature is affected by the surrounding environment. As a pool high up on the shore is exposed to the open air for longer periods, its temperature is affected by the air temperature, and direct heating from the sun, more than a lower shore rock pool. This results in inhabitants of the upper shore rock pool having to withstand more extreme temperatures. Not only do they have to cope with the higher extremes, but also the rapid changes in pool temperature which occurs when the pools are covered or splashed by the sea, (Brehaut, 1982). However while experiments have shown that Enteromorpha is reasonably tolerant of temperature changes, They have also shown the same for Fucus serratus, (Boney, 1969).

There was one significant difference though, at temperatures above 30 OC, the respiration rate of Fucus serratus greatly increased, (Boney, 1969). It should also be noted though, that the temperature recorded for the upper shore rock pool was less than 25 OC, and this was in the middle of an unusually hot day, with little cloud cover. So it is unlikely that submerged Fucus serratus at Bracelet Bay would have to cope with temperatures above 30 OC long enough for it to be a serious problem. But, what about high temperatures at times of exposure? There are two main problems associated with exposure - resisting desiccation and maintaining photosynthesis. Fucus serratus and Enteromorpha are both able to survive substantial water loss (60% - 90%), Nybakken, 1988).

Fucus serratus though, suffers a much more significant loss in rate of photosynthesis, (Boney, 1969). Ulva suffers greatly from drying out due to little morphological adaptations to retain water (c. f. F. serratus and particularly Enteromorpha intestinal is), (Boney, 1969). When looking for reasons why F. serratus and U. are less prominent further up the shore, their relative abilities to coloni se the pools should be considered. F. serratus struggles to efficiently coloni se the upper shore because the spore lings growth is inhibited with excessive exposure, (Boney, 1969), and young fucoids are more likely to be dislodged by wave action, (Raffaelli and Hawkins, 1996). It is also likely that Ahnfeltia corral ina can't survive prolonged periods of insolation.

Green algae is generally thought not to prosper when greatly submerged, as less red and blue light is available, resulting in a decrease in photosynthesis rates, (Begon et al 1986). IN fact, green algae spore lings show much reduced rates of growth, when subjected to low light intensities. Contrastingly, red algae spore lings showed an increase growth rate at low light intensities, (Begon et al 1986). The results reflected this fact to a degree, as, in the intertidal region studied, green (and blue) algae dominated, with red algae only being found in the lower shore. The lower shore rock pool was much shallower than the upper, but the overwhelming presence of green and blue algae in the deeper rock pool suggests that, the time the pools are covered by the sea, may be a more important factor when it comes to rates of photosynthesis. It is often the case that fucoids need an already existing layer of green algae present before it can coloni se.

This is due to the protection the green algae gives the Fucus from limpets and periwinkles, (Nybakken, 1988). Grazing by periwinkles and limpets is thought to be an overriding factor in determining whether algae colonies an area, (Nybakken, 1988). Limpets, when present, have been shown to decrease the amount of Fucoids in relation to the other sea weeds, (Boney, 1969). Both Patella depress and Patella vulgate were found in the upper shore rock pool but not the lower. This is perhaps reflected by F. serratus being in relative greater numbers in the lower shore rock pool. But if it is so difficult for F. serratus to coloni se the upper shore, how come it was still found the rock pool?

Perhaps the fact that Littorina prefer to feed on U. and Enteromorpha than Fucoids gave F. serratus a slight advantage. And also, Fucoids, if they are able to coloni se, tend to grow faster than the other algae, (as long as conditions aren't too unfavourable). It should also be noted that in the absence of Fucoids, Enteromorpha prospers as it is faster growing than other green algae, (Raffaelli and Hawkins, 1996), as long as numbers of Littorina aren't high, (which they weren't in the upper rock pool). This fact was reflected in the results, although Enteromorpha was unable to coloni se the lower rock pool. The red algae found, Corr alina officinal is, was found only in the lower shore. This is because while they can tolerate severe wave action, due to deposition of calcium carbonate, during periods of severe insolation they bleach quickly.

This is more severe when evaporation occurs, (Boney, 1969), as it more frequently does in the upper shore, (reflected by the higher temperature recorded). The presence of sea weed is vital to the survival of rock pool animals. Most of the animals found in the rock pools were herbivorous, feeding on algae of some form or another. And in the lower shore rock pool, it's likely that interactions between animals and plant life is a major factor in determining he variety and abundance of organisms there.

This is less likely to be the case in the upper shore, where abiotic rather than biotic factors are of greater importance, (Brehaut, 1982). The upper shore is a considerably harsher environment than that of the lower. Because of this, the organisms of the upper rock pool have had to become adapted to the abiotic factors they encounter there. Littorina litt orea is a characteristic feature of intertidal regions, and more particularly the middle and upper shore, (especially in the absence of L. ), (Boaden and Seed). As L. litt orea is better able to cope with the conditions of the upper rock pool, it is possible for it to compete better with other herbivores. L. litt orea's competitors would normally completely out compete them in a sublittoral or near sublittoral environment, as they are more efficient feeders and colonisers. But as you move up the shore and the conditions become harsher, due to greater abiotic fluctuations, it's a different story.

In the upper shore, the organisms are competing just as much with the abiotic factors as they are their competitors, if not more, (Brehaut, 1982). The conditions already discussed, which the algae have to be able to tolerate, are very similar for the animal life of the rock pools. So just like the algae, the animals of the rock pools would have to withstand desiccation when exposed. Consequently those organisms of the upper shore would probably have better adaptations to avoid desiccation, than those found in lower shore. Looking at the results it is clear that limpets prosper more in the upper than lower shore. P. depress a and P. vulgate are able to avoid desiccation by either clamping down tightly onto the rocks surface, or by retreating to a "home scar" into which their shells fit snugly, (Nybakken, 1988).

Limpets are also able to leave a small opening when exposed, so that air can reach the gills, with oxygen diffusing across a watery film. This allows them to respire when exposed, with little evaporation from the mantle cavity, (Brehaut, 1982). Littorina, already mentioned as being adapted to upper shore conditions, are able to reduce desiccation by retreating into their shells, and covering the opening of the shell with an operculum, (Brehaut, 1982). L. litt orea are also able to feed when exposed if the conditions are humid enough. L. litt orea can't respire when exposed, unlike the closely related L., which has a reduced and a highly vascularised epithelium in the mantle cavity, (Brehaut, 1982). This is one reason why L. should have been more frequent in the upper rock pool. Perhaps they weren't, due to the size of the rock pool studied. Litt orea sp. are able to withstand high temperatures when out of water - over forty degrees.

This may give them an advantage over other competitors, (Brehaut, 1982). Littorina litt orea, along with Patella sp. are also able to decrease their metabolic rate when exposed. It should be the case that those animals found in the lower shore, but not in the upper have problems dealing with harsher conditions. This is certainly the case with Nucella pap illus, which is quite abundant in the lower shore rock pool, but not present at all in the upper rock pool. This is due to, Nucella pap illus suffering from excessive desiccation in the upper intertidal areas, as well as needing a long period of submergence to attack prey successfully, (usually Balanus - not usually found in the middle or upper shore), plus it suffers from heat coma at 28 OC, (Boaden and Seed). The most abundant animal in the lower rock pool was Gibbula umbilical is, which was a little surprising as it is able to maintain a similar respiration rate in and out of the water, unlike G. cineraria, (Brehaut, 1982).

This means that G. umbilical is should be more abundant than G. cineraria in the upper rock pool, but G. cineraria was present in small numbers in the upper rock pool, while G. umbilical is wasn't even present. Perhaps this was because of different feeding preferences or related to the different pool sizes. Carcinus maen us was found in the upper rock pool, this was not surprising, as it has an abundance of food such as molluscs, and it is able to cope with the conditions being and having specialised respiration, (Brehaut, 1982). As expected, all the organisms found in the rock pools had methods of protecting themselves against wave action.

The algae had strong holdfasts, the gastropods adhesive foots using suction and in some cases secretion as well, (e.g. Patella), (Brehaut, 1982). Some of the organisms have adapted body shapes as well, e.g. the short shell of L. litt orea. As predicted, the number of organisms in the lower rock pool was greater than that of the upper, relative to the respective sizes of the pools. This is because less organisms can tolerate the harsher conditions, with abiotic factors becoming a considerable selection pressure.

The temperature in the upper rock pool was considerably higher than that of the lower, and the oxygen content of the upper rock pool was a lot less than that of the lower rock pool. However there was not quite as much difference between pH and salinity as expected, this was most likely to do with the much greater size of the upper rock pool.

Bibliography

Begon, Harper & Townsend, (1990), 'Ecology, individuals, populations and communities', second edition, London: Blackwell scientific publications.
Boaden, P.J.S. & Seed, R. (1985), 'An introduction to coastal ecology', London: Blackie.
Brehaut, Roger, N. (1982) 'Ecology of rocky shores', London: Edward Arnold Ltd.
Boney, A.D. (1969), 'A biology of marine algae'.
London: Hucthinson Educational. Raffaelli, David & Hawkins, Stephen, (1996), 'Intertidal Ecology', London: Chapman & Hall.