Chapter 7 - Benthic Macrofauna Communities

Abstract

Physical and biological factors operating over many spatial scales govern community features of sandy-beach macrofauna. At the macroscale, species richness decreases from tropical to temperate beaches and from macrotidal dissipative beaches to microtidal reflective beaches. At the mesoscale, longshore and across-shore distributions tend to be unimodal, bell-shaped within a beach, with abundance varying from the central region to range boundaries, though environmental gradients (wave exposure and salinity) can cause asymmetries. Zonation is highly dynamic and not sharply defined because of short-term (hourly, daily) or medium-term (seasonal) reactions to environmental conditions, passive transport and sorting by the swash (e.g., by recruits), active microhabitat selection (e.g., by adults), and intra- and interspecific interactions. At the microscale (individual neighbourhood or quadrat scale), behavioral factors and intra/interspecific interactions become more important when density increases as a result of limitation of space, and vertical partitioning of the sediment habitat occurs. Several conceptual models relating biological descriptors and physical variables are outlined, linking processes, mechanisms, and patterns at a variety of spatial scales. Unexplored fields of research are highlighted.