A new technique for evaluating short-term rates of coastal bioerosion and bioprotection Larissa A. Naylor * , Heather A. Viles School of Geography and the Environment, University of Oxford, Mansfield Road, Oxford OX1 3TB, UK Received 30 March 2001; received in revised form 13 February 2002; accepted 4 June 2002 Abstract A multi-scale and multi-method approach has been developed to evaluate the nature and effects of short-term biological colonisation. This method has been used at Falasarna, on the western coast of Crete, to investigate bioprotection and bioerosion on a microtidal rocky coast. Eighteen blocks of limestone (5 Â 5 Â 2 cm) were exposed for 7 months (September 1998 to April 1999) at mean sea level at two exposed sites and one sheltered site. Biological colonization and its impacts were assessed by optical microscopy (OM), scanning electron microscopy (SEM) and multiphoton laser scanning microscopy (MPLSM). Exposed sites became colonized more quickly than the sheltered site and once a cover of foliose and filamentous algae had become established, bioerosion (by cyanobacteria), biological etching and chemical weathering were reduced. Consequently, there appears to be an inverse relationship between macroalgal abundance and bioerosion of experimental substrata after 7 months of colonisation. Thus, some level of bioprotection appears to be provided by macro algae under exposed site conditions and would probably become increasingly apparent in longer-term research trials. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Mediterranean limestone coasts; Exposure block trials; Multiphoton microscopy; Biological colonisation; Biogeomorphology 1. Introduction Limestone coasts are commonly influenced by a range of biogeomorphic processes, such as bioerosion, bioconstruction and bioprotection. Of these, bioerosion and bioconstruction have received the most attention in the past, whilst bioprotection (which can be defined as the protection of surfaces by organisms and biocon- structions from other geomorphic processes) has been largely neglected. Studies of bioerosion have com- monly attempted to quantify the rate and style of erosion effected by one or more types of organism and their contribution to coastal morphology (see, for example, the work of Schneider, 1976; Torunski, 1979 on the Istrian coast in the northern Adriatic Sea and Trudgill and others on the coast of Co. Clare, Ireland (Trudgill, 1987; Trudgill and Crabtree, 1987; Trudgill et al., 1987)). In contrast, studies of bioconstructions have often focused on their role as indicators of sea level, alongside their role in shaping the coastal profile (e.g., Dalongeville, 1995 in the Mediterranean; Focke, 1978 in the Caribbean; and Laborel and Laborel- 0169-555X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0169-555X(02)00139-3 * Corresponding author. Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK. Tel.: +44-1603-593910; fax: +44- 1603-593901. E-mail address: l.naylor@uea.ac.uk (L.A. Naylor). www.elsevier.com/locate/geomorph Geomorphology 47 (2002) 31 – 44