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Abstract:
Physical sedimentological processes such as the mobilization and transport of shelf sediments during extreme storm events give rise to disturbances that characterize many shelf ecosystems. Connell’s (1978) intermediate disturbance hypothesis predicts that biodiversity is controlled by the frequency of disturbance events, their spatial extent and the amount of time required for ecological succession. A review of available literature suggests that periods of ecological succession in shelf environments range from 1 to over 10 years. Physical sedimentological processes operating on continental shelves having this same return frequency include synoptic storms, eddies shed from intruding ocean currents and extreme storm events (cyclones, typhoons and hurricanes). Research by physical sedimentologists has shown that the results of such storms may include bed stresses that cause widespread erosion, deposition of storm beds over 1 m in thickness and destruction of seagrass beds as well as bioherms such as coral reefs. Published models of extreme storms indicate their influence may extend to over 100km from the pressure-centre of the atmospheric depression. Modelling studies carried out by Hemer (2006) to characterize the Australian continental shelf in terms of bed stresses due to tides, waves and ocean currents from an 8-year time series may represent temperate synoptic storms in southern Australia but the time series is probably too short to represent tropical cyclones in northern Australia. Information such as this is essential to marine managers charged with the design of marine protected areas (MPAs) and other conservation measures aimed at protecting and preserving biodiversity in the oceans. Further studies are needed to compare model output and measures of shelf disturbances to the spatial and temporal variations associated with shelf ecological successions.
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