Abundance and diversity of the sublittoral meiofauna on two sand beaches under different hydrodynamic conditions at Ilha do Mel (PR, Brazil)

Abstract

The meiofaunal community of two hydrodynamically different sand beaches was studied at Ilha do Mel, Paraná state (25°29′ S and 48°17′ W), Brazil. The sediment at a sheltered site and at a site exposed to open ocean was dominated mainly by fine sand. At the sheltered site the sediment was less sorted, with some clay, silt and organic matter. Sea water salinity and temperature did not differ between the two sites. Total meiofauna and Nematoda densities were greater at the exposed site. The high vertical migratory capacity of Nematoda in comparison with other meiofaunal taxa, and the almost complete absence of other interstitial meiofaunal groups could explain this pattern. High resistance to environmental impacts (i.e. turbidity) could be another possible explanation for the high Nematoda densities at the exposed site. On this basis, the low Nematoda/Copepoda ratio at the sheltered site could be an indication of moderate hydrodynamic stress at this place, since Copepoda are more sensitive to environmental disturbances than Nematoda. Copepoda densities, Shannon diversity (log 2), and evenness indices were higher at the more eutrophic (sheltered) site. Cluster analysis showed that replicated samples were more similar within each site (sheltered or exposed) than between them (sheltered x exposed), thus illustrating a possible response of meiofaunal taxa to environmental differences imposed by different hydrodynamic regimes.