Abstract This study evaluated the effects of biogenic structures (tree roots and crab burrows) on sediment carbon (C), sulfur (S), and iron (Fe) biogeochemistry during the wet season in the Olaria mangrove forests near the city of Cananéia, São Paulo state, Brazil and the Nobrega mangrove forest approximately 2 km from the city. Anaerobic C oxidation pathways were assessed from sediment profiles and anaerobic incubations and related to the abundance of biogenic structures in the form of pneumatophores and crab burrows. Porewater depth profiles of dissolved inorganic carbon (DIC) and SO42- were less steep in the presence than absence of biogenic structures. While Fe(II) appeared unaffected by biogenic structures, Fe(III) levels were significantly higher in the upper 4 cm of the sediment in the presence than absence of vegetation and bioturbation. Surprisingly, the concentration of Fe(III) in this layer was 2-6 times higher in the Nobrega forest (6-13 µmol cm-3) than in the Olaria forest (1.5-6.5 µmol cm-3). Accordingly, depth integrated sulfate reduction (SR) tended to be highest at Olaria, while iron reduction (FeR) was highest at Nobrega. SR accounted for 54-83% of DIC production, with no diference between forested sites, while FeR accounted for 8-24% of DIC production, with a 2-3 times higher contribution in the Nobrega versus the Olaria forest. The results suggest that mangrove roots and crab burrows in mangrove sediments only promote FeR at the expense of SR in the Nobrega forest. It appears that anthropogenic discharge from Cananéia city may have overridden the impact of biogenic structures on sediment redox conditions at Olaria, thereby diminishing the role of FeR without strong stimulation of overall C oxidation rates.

O presente trabalho analisa e descreve a estrutura das associações faunísticas macrobênticas (epifauna e infauna) do sistema estuarino da Baía de Vitória, sudeste do Brasil, de Janeiro de 1998 a Junho de 1999. Amostras replicadas em níveis de entre-marés e sublitoral foram coletadas em intervalos de três meses em dez estações. Foram caracterizadas as composições dos sedimentos de entre-marés e sublitoral. Os parâmetros físico-químicos da água foram medidos in situ. Foram coletados 10.695 indivíduos, compreendendo a 144 taxa. Os grupos mais abundantes foram moluscos, crustáceos e poliquetos. As espécies mais abundantes foram os bivalves Anomalocardia brasiliana, Mytella guyanensis e M. falcata. Localmente, descargas significativas de esgoto doméstico causaram um aumento da quantidade de matéria orgânica no sedimento (até 30%) e baixa concentração de oxigênio dissolvido na água (< 1mg.l-1). Próximo às duas entradas da baía, o alto hidrodinamismo e a presença de areia grossa reduziram os efeitos deletérios dos aportes de esgotos. A riqueza (S), a diversidade (H') de espécies e a abundância total (A), decresceram das estações externas do estuário (22 < S < 72; 1.99 < H' < 2.85; 320 < A < 1737) em direção às estações internas (2 < S < 45; 0.59 < H' < 2.67; 2 < A < 1317), onde a salinidade e oxigênio dissolvido foram menores e as quantidades de matéria orgânica maiores.

The present work describes and analyses the structure of the macrobenthic epi- and infaunal assemblage of the estuarine system of Vitória Bay, South-eastern Brazil, from January 1998 to June 1999. Replicated sampling at intertidal and subtidal levels was conducted quarterly at ten stations. Intertidal and subtidal sediment composition was characterised. Water physico-chemical parameters were measured in situ. A total of 10,695 individuals, belonging to 144 taxa, were collected. Molluscs, crustaceans and polychaetes were the most abundant groups. The bivalves Anomalocardia brasiliana, Mytella guyanensis and M. falcata were the most abundant species. Locally, significant discharges of residential and industrial wastewater resulted in high organic content in the sediment (up to 30%) and low dissolved oxygen concentration in the water (< 1mg.l-1). Near the two entrances of the bay, high hydrodynamic activity and coarse sand reduced the detrimental effects of raw and treated sewage inputs. Species richness (S), diversity (H') and total abundance (A) decreased from outer-bay stations (22 < S < 72; 1.99 < H' < 2.85; 320 < A < 1737) towards inner-bay stations (2 < S < 45; 0.59 < H' < 2.67; 2 < A < 1317), where salinity and dissolved oxygen were lowest and organic matter content highest.