The role of above- and below-ground components of Spartina alterniflora (Loisel) and detritus biomass in structuring macrobenthic associations of Paranaguá Bay (SE, Brazil)

The influence of Spartina alterniflora marshes and detritus availability on the spatial structure and time variability of macrobenthic associations was investigated in Paranaguá Bay, a subtropical estuary in southern Brazil. Four sampling sites were established along the salinity and exposure gradient of Paranaguá Bay in the winter and summer of 1992. At each site, 5 samples (0.02 m2corer) were taken in the salt marshes and adjacent unvegetated tidal flats. Sediment composition, salt marsh structure (stem height and density, live and dead above- and below-ground biomass of S. alterniflora) and vegetal detritus biomass were determined to assess whether they can affect the dynamics of macrobenthic invertebrates. The development of salt marshes and the amount of detritus, the latter mainly originated from adjacent mangroves, were determined by the energy and salinity gradients along the bay. Plant above- and below-ground components, together with detritus biomass, exert a strong influence on the composition and distribution of macrofauna in Paranaguá Bay. Salt marshes support higher densities and species number of macrobenthic invertebrates. Multivariate analyses showed that oscillations of different fractions of Spartina alterniflora, as well as detritus availability, affect the different components of macrobenthic associations in a variable degree. Spatial and temporal shifts of infaunal organisms appear to be more evident than those of mobile epibenthic forms.