Biological Zonation and Bedrock Strength on a High Energy Granite Shore Platform

Abstract

Burningham, H. and Knight, J. 2020. Biological zonation and bedrock strength on a high energy granite shore platform. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 23-28. Coconut Creek (Florida), ISSN 0749-0208.Many studies have shown that downwearing of rock shore platforms results from interactions between biological and geomorphological processes, but the relative roles of biological, lithological and external (wave hydraulic action) in shaping rock shore platforms have not been examined in detail. This is important, however, because surface organisms can both increase and decrease rates of platform downwearing by biological weathering and bioprotection, respectively. This study presents biological and geomorphological results from a high energy shoreline in northwest Ireland. Here, the 50-100 m wide granite shore platform has a slope of ∼1:6 and extends from 7-9 m above the level of mean high water springs to ∼2 m below mean low water. Organisms attached to the bedrock surface were surveyed by the quadrat method along two shore-normal topographic transects. At each quadrat site, bedrock hardness was measured using an Equotip instrument. Results show clear ecological zonation that can be directly related to the tidal frame. There is very little evidence for cross-shore changes in bedrock hardness. Elevation is the most significant driving factor for the presence of different species, but bedrock hardness is only associated with the abundance of specific species such as barnacles, demonstrating complexity in biogeomorphological relationships at local scales.