BIOLOGICALLY GENERATED HABITAT PROVISION AND DIVERSITY OF ROCKY SHOREORGANISMS AT A HIERARCHY OF SPATIAL SCALES

The diversity and abundance of intertidal organisms found on moderatel y exposed shores were compared between biologically generated complex and less complex habitats at four different spatial scales. For macrob iota, comparisons were made between Fucus clumps and open areas (barna cle covered or bare rock) and then between barnacle covered rock and ' bare' rock. Microbiota were compared on barnacle plates and on the roc k surface and at a finer resolution on the plates themselves and pits in the plates. Macrobiota were quantified at two levels of resolution by direct observation and under low power magnification. Microbiota we re examined at two levels of resolution with a scanning electron micro scope. For macrobiota the average number of species was significantly greater in complex habitats at both levels of resolution. The average number of individuals associated with the Fucus clumps was significant ly lower than that on adjacent areas of barnacle covered and bare rock . However, the average number of individuals associated with the barna cle matrix was significantly greater than that on surrounding rock. Th e differences were entirely caused by a greater abundance of barnacles and species associated with the barnacle matrix on exposed rock outsi de the Fucus clumps. For microbiota there were large differences in sp ecies composition; cyanobacteria were predominant on the rock surface whilst diatoms dominated the barnacle plates. The diversity of this as semblage was low and no differences in species numbers were apparent b etween the two habitats. At a finer scale, abundance of individuals wa s much greater in the pits than on flat areas of the surrounding plate s and there was a slightly elevated average number of species per samp ling unit. This paper illustrates the importance of using a variety of resolutions to measure biodiversity and the importance of biological habitat provision in maintaining biodiversity.