Gastropods and intertidal soft-sediments: The case of Chilina ovalis Sowerby (Pulmonata : Basommatophora) in south-central Chile

Field experiments (exclusion and inclusion of gastropods) were carried out in the intertidal of the Lingue River estuary (south-central Chile) during the summers of 1991 and 1992. Cages were used to analyze the effects of the snail Chilina ovalis Sowerby on the macroinfaunal community structure and the sedimentological properties of the top (1.5 cm) layer of the substrate. The experiments lasted 30 (1991) and 90 days (1992). We also studied the q uality of sediment in snail trails versus sediment without trails, and the abundance and size structure of C. ovalis over a period of 15 months. In bo th field experiments, C. ovalis affected neither the macroinfaunal structur e nor the sediment quality. Significant differences were detected for chlor ophyll a content (phytobenthic biomass) when disturbed (trails sediment) ve rsus undisturbed sediment were compared. The highest abundance of C. ovalis (up to 792 ind/m(-2)) occurred during summer months when the experiments w ere carried out. It is concluded that the disturbance of intertidal sedimen t by C. ovalis is quite local and of short duration, a situation which is d iscussed in connection with physical and biological factors involved in sed iment stability and community organization of macroinfaunal assemblages.