Early studies on sandy beach zonation patterns haveshown rather rigid schemes. Recent work has suggested thatzonation changes with morphodynamic type and, in dissipativebeaches, it also changes through time. This last finding leads to theconclusion that at least 1 yr of study is necessary to understandzonation patterns in dissipative sandy beaches. Here we report a 1yr study (from March 1994 to March 1995) of 4 microtidal beacheswith different morphodynamic types situated on the Atlantic coastof Uruguay. We show that zonation patterns (number of zones orbelts) can change through time regardless of beach type. However,the morphodynamic characteristics of the beach seem to affecthow frequently the zonation pattern can change by fusion orsubdivision of zones, and which zones are involved in thoseprocesses. In beaches with flat slopes (toward the dissipativeextremity), the lower zones were frequently fused and divided. Thesame occurred with the medium and upper zones in the beacheswith steeper slopes (towards the reflective extremity). Our resultssuggest that spatial variability of the macrofauna is related tovariability in the position of the swash zone, which in turn dependson beach slope and width. Variability of species distribution wouldalso depend on morphological adaptations of organisms to movein such environments. We suggest 2 mechanisms of speciesmovement to explain the variability in species distribution observedin this study: Swash Mediated Active Movement (SMAM) andAutonomous Active Movement (AAM). The first mechanisminvolves both an active and a passive component. AAM isindependent of swash movements and affects species distributionon the upper levels of the beach.