Baseline assessment of mollusc assemblages from different intertidal rocky shores of Southern Patagonia

Abstract

Mollusc species are ecologically and economically important, acting as fishery resources, ecosystem engineers, bioindicators, and invasive species. However, their study in Southern Patagonian rocky shores remains limited. This research aimed to study the mollusc assemblages and to explore the effect of environmental variables (salinity regime, wave exposure and seasonality) and substrate characteristics (inclination and elevation) on community descriptors. A seasonal sampling was conducted at two sites in Bahía San Julián: one exposed to wave action (SJO) and one sheltered (SJI). Additionally, a sheltered estuarine site was studied in Río Gallegos (RGE). The results showed that at lower horizontal substrates species richness was highest in exposed marine environments (SJO: 7–19 spp.), followed by sheltered marine (SJI: 5–13 spp.) and estuarine environments (RGE: 2–8 spp.). Total density peaked in exposed-marine environments at upper substrates (SJO: 23,000–38,000 ind/m2) and was lowest at lower substrates (ca. 2200–13,000 ind/m2), considering both orientations (horizontal and vertical). A distinct composition of mollusc assemblages were determined between sheltered-estuarine (RGE) and marine environments (SJI and SJO), and between substrate characteristics. The explained variation of mollusc abundance, was attributed mainly to salinity regime (32.8%), followed by substrate elevation (14.7%), wave exposure (10.1%) and substrate inclination (9.0%). Suspension feeders were the dominant group in all study sites. Our findings suggest that species richness, density, and diversity of mollusc assemblages are synergistically determined by environmental variables and substrate characteristics. The present study provides essential information for developing marine biodiversity conservation programs in Southern Patagonia.