Freshwater mollusk trophic guilds, composition and distribution in the fluvial landscape of a Brazilian subtropical stream

Abstract

This study verified spatial standards concerning freshwater mollusk trophic guild proportions, composition and distribution along the gradient of fluvial landscape units throughout the Velhaco stream, a subtropical stream located in Rio Grande do Sul state (Brazil). Quantitative collections (presence and absence) were made at six sampling stations distributed throughout the stream’s fluvial landscape units: Headspring Sector (SI), Proximal Intermediate Sector (SII), Distal Intermediate Sector (SIII), and Final Sector (SIV). Through the clustering (Jaccard coefficient, group linkage method of centroid) and Bray-Curtis polar ordination (similarity measure of Jaccard) analyses, a longitudinal species distribution pattern was verified within the gradients of the fluvial landscape units. Suspension feeders were dominant, except at SI. Species compositions at SI and SII (lower species richness) were related to their higher altitude, thicker sediments, greater oxygenation and higher pH. On the other hand, species compositions at SIII and SIV (higher species richness) were related to their larger hierarchical channel, larger width, larger depth, greater sinuosity, finer sediment and greater aquatic macrophyte richness. Contrary to the RCC predictions, the highest species number was not verified in the stream’s middle stretch, but in the end stretch.

Keywords

• Fluvial landscape
• Freshwater molluscs
• River continuum concept
• Trophic guilds