Distribution and abundance of hydrobiid snails in a mixed estuary and a coastal lagoon,Argentina

This study examined the environmental factors influencing the distribution and abundance of hydrobiid snails in two estuaries on the northeastern coast of Argentina in a coastal lagoon (Mar Chiquita, 37°40′S, 57°20′W) and a partially mixed estuary (Quequén Grande, 38°30′S, 58°45′W). Five intertidal study sites in each estuary represented a gradient in environmental conditions. Variations in the main environmental factors and in the abundance of hydrobiids were assessed both spatially and seasonally. The three species wereHeleobia australis, Heleobia conexa, andHeleobia parchappii, and they were primarily distributed across a salinity gradient. This pattern was clearly recognizable in the partially mixed estuary, where the abundance ofH. australis decreased as salinity decreased, and the abundance ofH. conexa gradually increased towards the inner reaches of the estuary.H. parchappii was restricted to areas far away from the influence of the tide. Slight differences in the distribution patterns of these species between Quequén Grande and Mar Chiquita were refated to the different dynamics of environmental factors in each estuary.