INFLUENCE OF TOPOGRAPHIC HETEROGENEITY AND SPATIAL SCALES ON THE STRUCTURE OF THE NEIGHBORING INTERTIDAL ENDOBENTHIC MACROFAUNAL COMMUNITY

The influence of topographic heterogeneity (boulders of different size s: 0.75, 1.5, 2.25 m) on intertidal soft-bottom community characterist ics [diversity(H') richness, and biomass] was examined in the St, Lawr ence Estuary, Canada, The macrofauna, sediment characteristics, and fl ow regime in the zones surrounding boulders were examined in 6 orienta tions (directions) and at 3 distances from boulders. Flow around bould ers and control sites (no boulders) was estimated by the rate of plast er dissolution of standard plaster cylinders. Control sites (no boulde rs) showed the highest species diversity (H'(a): based on density) and richness. These parameters decreased significantly with boulder size and increased significantly with distance from boulders. For both smal l and large boulder sizes, highest and lowest diversities were general ly observed in opposite orientations. Overall, biomass was not influen ced by boulder size. Plaster dissolution explained more variability in diversity, richness and biomass (up to 35, 30 and 25 %, respectively) than did sediment characteristics (8, 6 and 27 %, respectively). Spec ies dominance was strong and probably explained the relative constancy of diversity among treatments.