Variation in physical factors is considered the primary organizational force regulating macrobenthic populations and communities of exposed sandy beaches. However, there has been no quantitative evaluation of the intensity of human predation on the macrofauna inhabiting these systems, and information on biological interactions is also lacking. In the present study I review the results of a long-term monitoring study on the yellow clam Mesodesma mactroides (Deshayes, 1854) (Bivalvia: Mesodesmatidae) of an Uruguayan exposed sandy beach, including the effect of a human exclusion experiment as a way to acquire knowledge about its population structure and dynamics. Experimental management was based on the closure of the fishery for 32 months, in which a great part of the artisanal fishery community and the coastal marine authorities were involved in control operations. The experiment was a useful approach to testing the effect of fishing disturbing or altering the yellow clam population: the wide range of fishing effort levels through time allowed the detection of some patterns and
processes that until the closure were unknown, namely: (I) the stock recruitment-relationship showed overcompensation, i.e. the inhibition of recruitment at highest adult densities: (2) growth rates of the newly settled cohorts were inversely correlated with the corresponding average adult density: (3) post-settlement natural mortality was htghest in the densest cohorts, and was also a function of fishing activity: (4) the amount of fishing effort exerted over Mesodesma mactURides explained variations in abundance of the sympatric population of the wedge clam Donax hanleyaQXs Philippi, 1845 (Bivalvia: Donacidae). It is concluded that experimental management is a powerful approach to identify factors governing the dynamics of exploited sandy
beach populations, to acquire the basic biological knowledge needed to perform adequate management strategies and to quantify the effect of harvesting on other components of the macrofauna. It is also stressed that further research in sandy beach populations should include human activities as important factors affecting long-term trends.