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BA Research
Dissertation Abstract: 'A comparison of bioerosion and bioprotection in Northern Chile and the Isle of Mull'Previous work on shore platforms has concentrated principally on sedimentary carbonate rocks. In this study, basic igneous shore platforms in Northern Chile and the Isle of Mull, UK of similar provenance, are compared. Bioerosion and bioprotection, defined respectively as the propensity of organisms to directly or indirectly erode or protect rock, are compared for a range of climatic and exposure environments at a variety of spatial scales.
Microscopical techniques, including optical microscopy, thin sectioning, and Scanning Electron Microscopy, are used on samples of rock from various sites to test whether bioerosion at the micro-scale is biologically controlled. Experimental evidence suggests that it is not, and that bioerosion is for the micro-scale a physically delimited phenomenon.
At the scale of individual shore platforms (meso-scale), Ballantine's (1961) biologically defined exposure scale is used to grade shores ranging from extremely exposed to extremely sheltered. A variety of integrated geomorphological-ecological field techniques based on Trudgill (1988) are used to qualify and quantify morphological and ecological features on the shore. Focke's (1978) hypothesis is proposed, i.e. that bioerosion is the dominant mechanism of geomorphological change on sheltered shores and bioprotection is the dominant mechanism on exposed shores. However, using the Chi2 and F-test for variances, no association is found to exist between bioeroders and sheltered shores, nor between bioprotectors and exposed shores. An alternative hypothesis by Wright et al. (1987), stating the association of bioeroders with exposed shores, is instead found to be partly true. The degree of shore exposure is concluded to be the controlling factor governing bioerosion on the shore, subject to the scale at which the shore is studied.
Questions are posed regarding the overall controlling mechanism of erosion on the shore. By the use of t-tests, correlation, and regression to test for association between particular features, mechanical erosion is shown to be dominant at the largest scale and to be influenced ultimately by climatic environment. No fundamental differences in the criteria tested are found between shores in Chile or Mull, aside from climatically controlled differences in ecological abundance. Based on these findings, a theoretical nested hierarchy system is proposed to operate at a variety of scales in shore development. The need for integrated temporal-spatial scale studies is identified and speculations are made regarding shore platforms as complex, non-linear systems that appear to display evidence of self-organising behaviour.
References
Ballantine, W.J., 1961, A biologically-defined exposure scale for the comparative description of rocky shores. Field Studies, 1(3), 1-19
Focke, J., 1978, Limestone cliff morphology on Curacao. Zeitschrift fur Geomorphologie, 22, 329-249.
Trudgill, S.T., 1988, Integrated geomorphological and ecological studies on rocky shores in Southern Britain. Field Studies 7, 239-79.
Wright et al, 1987, The morphodynamic effects of incident wave groupiness and tidal range on an energetic beach Marine Geology 74, 1-20