Multifractal spatial distribution of epilithic microphytobenthos on a Mediterranean rocky shore

Understanding how patterns and processes relate across spatial scales is one of the major goals in ecology. 1/f models have been applied mostly to time series of environmental and ecological variables, but they can also be used to analyse spatial patterns. Since 1/f noise may display scale-invariant behaviour, ecological phenomena whose spatial variability shows 1/f type scaling are susceptible to further characterization using fractals or multifractals. Here we use spectral analysis and multifractal techniques (generalized dimension spectrum) to investigate the spatial distribution of epilithic microphytobenthos (EMPB) on rocky intertidal surfaces. EMPB biomass was estimated from calibrated colour-infrared images that provided indirect measures of rock surface chlorophyll a concentration, along two 8-m and one 4-m long transects sampled in January and November 2012. Results highlighted a pattern of spectral coefficient close to or greater than one for EMPB biomass distribution and multifractal structures, that were consistent among transects, implying scale-invariance in the spatial distribution of EMPB. These outcomes can be interpreted as a result of the superimposition of several biotic and abiotic processes acting at multiple spatial scales. However, the scale-invariant nature of EMPB spatial patterns can also be considered a hallmark of self-organization, underlying the possible role of scale-dependent feedback in shaping EMPB biomass distribution.