Landscape pattern indices applied to Mediterranean subtidal rocky benthic communities

Abstract

Marine rocky benthic communities present rich contrasts in spatial pattern. Its quantification is a prerequisite for the comparison of spatial pattern across communities, for the evaluation of temporal changes, and for the analysis of the effects of pattern on ecological processes. This study pursues two goals: (1) to evaluate the potential application of landscape pattern indices to the description of spatial pattern in Mediterranean subtidal rocky benthic communities, and (2) to select a minimal set of informative, non-redundant indices for the description of spatial pattern in these communities. Four communities dwelling along a depth gradient were studied, two dominated by algae, and two dominated by clonal animals. The communities differed in species composition, dynamics and structure. Using traditional methods, previous studies had determined that, along this depth gradient, the heterogeneity of community spatial patterns increases, and their seasonal dynamics becomes dampened. We used a series of photographs (310 cm2 each) of permanent sites taken monthly over a one year period to analyze community spatial pattern. We tested a total of 17 landscape pattern indices that quantify different aspects of spatial pattern (patch size and shape characteristics, diversity, contagion and interspersion), for differences among communities, and for differences through time within each community. Results show clear differences in patch characteristics (number, mean size, size variability and shape), diversity, contagion and interspersion indices, among communities. In some cases, significant temporal patterns were also found, and these were consistent with the seasonal dynamics formerly described for each community. Generally, spatial pattern was less heterogeneous, but more variable seasonally, in the shallower, algae-dominated communities, than in deeper communities dominated by clonal animals. These results indicate the existence of community-related characteristic spatial patterns, and characteristic spatial pattern dynamics, in subtidal rocky benthic communities. Moreover, trends found in this study were in agreement with previous studies of spatial pattern in Mediterranean rocky benthic communities. Based on this study, we selected number of patches, mean patch size, standard deviation of patch size, mean shape patch index, and Shannon's diversity index as the most suitable set of indices for the description of spatial pattern in Mediterranean subtidal rocky benthic communities.