Effects of submerged aquatic vegetation on macrozoobenthos in a coastal lagoon of the southwestern Atlantic

The freshwater-dominated part of Rocha coastal lagoon recently experienced sudden colonization by submerged aquatic vegetation (SAV). Macrophytes may be beneficial or detrimental for the zoobenthos, and both assemblages may in turn affect the food availability for birds and fishes. With the aim of evaluating the effect of SAV on water conditions and on the composition, abundance and diversity of macro-zoobenthos, vegetated areas (V, up to 500 g DW m(-2)) were compared with vegetation-free areas (N). The benthic abundance was higher in V (up to 5 000 ind m(-2)) than in N (up to 2 200 ind m(-2)). Species richness and abundance of amphipods, gastropods and chironomids were also higher at V compared with N. Conversely, the abundance of Tanais stanfordi (Crustacea), Erodona mactroides (Bivalvia) and Laeonereis culveri (Polychaeta), and the Shannon diversity were higher at N.