From a review of the literature on supra-littoral rockpools from the beginning of the century, it is shown that there in a paucity of knowledge on the community structure of these pools and the factors responsible for it. The methods used in the study are described and discussed. The physical and chemical changes in the water of nine supra-littoral roekpools at Greg Hess near Aberdeen are described and a classification of these pools based on salinity is put forward. The fluctuations in the nitrogen content of the bottom deposit of each pool are described and the main factors affecting it are discussed. It is concluded that it is derived principally from the micro-organisms which break down the dead fauna and flora to provide a rich supply of food for the living fauna. It is shown that the reproductive cycle of Enteromorpha intestinalis is accompanied by changes in the quantity of carbohydrate in the thalli. Large reserves are present prior to sexual reproduction, while smaller reserves are built up before sexual reproduction occurs. The quantitative distribution of E. intestinalis is not seriously affected by salinity in this region. It seems likely that E. intestinalis is the principal primary source of organic matter in the pools. The distribution of the fauna over the nine pools depends on the salinity tolerance range of the individual species and two main zones can be distinguished with a transitional zone of overlap between them. The harpacticoid, Tigriopus brevicornis dominates those pools with an overall salinity range 0.5%o - 45%o and Nitocra spinipes dominates those pools where the salinity does not rise above 35%o. The course of the life history of the principal members of the fauna is described and the causes of the fluctuations in the population density of each species in each pool are discussed. The community of each pool is made up of those species which can not only tolerate but can reproduce under the environmental conditions prevailing in each pool. The dominant organisms are the harpacticoid copepods but the balance can be upset by prolonged changed in the environmental conditions. Experiments to determine the relative importance of temperature and salinity on the survival of the harpacticoid copepods and the ostracod Loxoconcha baltica are described. Survival of T. brevicornis in hypersaline water improves as the temperature rises while lower temperatures favour survival of If. 3pinipes in hyposaline water. Mesochra lilljeborgi has a very narrow range of salinity and temperature tolerance. The females of all three species display a higher survival range than the males. Salinities below 35%o are optimal for L. baltica. Micro-organisms present in the bottom deposit form the principal food of T. brevicornis although E. intestinalis and other copepods, including its own species, can be utilised. Salinity affects the rate of food intake. It is concluded that salinity is the dominant factor affecting the organisms of the rockpool communities and their maintenance. Food supply is rarely a limiting factor. A scheme is presented of the zonation-and classification of supra-littoral rockpools based on salinity and faunal composition. The practical application of this scheme for other localities is discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:592253 |
| Date | January 1968 |
| Creators | Clark, Margaret E. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602194 |
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