Polychaete assemblage of an impacted estuary, Guanabara Bay, Rio de Janeiro, Brazil

Abstract

(Avenida Nazaré, 481, São Paulo, SP, Brasil) mdst@usp.br A B S T R A C T Thirty-eight stations were sampled in Guanabara Bay, Rio de Janeiro, Brazil, to assess the spatio-temporal diversity and biomass of sublittoral polychaetes. Samples were collected during the dry (September 2000) and rainy season (May 2001) in shallow sublittoral sediments. The polychaete spatial composition showed a heterogeneous distribution throughout the bay. A negative gradient of diversity and biomass was observed towards the inner parts of the bay and sheltered areas. A wide azoic area was found inside the bay. Some high-biomass and low-diversity spots were found near a sewage-discharge point. In these areas, the polychaete biomass increased after the rainy season. A diversified polychaete community was identified around the bay mouth, with no dramatic changes of this pattern between the two sampling periods. Deposit-feeders were dominant in the entire study area. The relative importance of carnivores and omnivores increased towards the outer sector, at stations with coarse sediment fractions. Guanabara Bay can be divided into three main zones with respect to environmental conditions and polychaete diversity and biomass patterns: A) High polychaete diversity, hydrodynamically exposed areas composed of sandy, oxidized or moderately reduced sediments with normoxic conditions in the water column. B) Low diversity and high biomass of deposit and suspension-feeding polychaete species in the middle part of the bay near continental inflows, comprising stations sharing similar proportions of silt, clay and fine sands. C) Azoic area or an impoverished polychaete community in hydrodynamically low-energy areas of silt and clay with extremely reduced sediments, high total organic matter content and hypoxic conditions in the water column, located essentially from the mid-bay towards the north sector. High total organic matter content and hypoxic conditions combined with slow water renewal in the inner bay seemed to play a key role in the polychaete diversity and biomass. Sedimentation processes and organic load coming from untreated sewage into the bay may have negatively affected the survivorship of the fauna. R E S U M OTrinta e oito estações foram amostradas na Baía de Guanabara, Rio de Janeiro, Brasil, no intuito de descrever a diversidade e biomassa de poliquetas sublitorais. As coletas foram realizadas em dois períodos distintos do ano: seco (Setembro 2000) e chuvoso (Maio de 2001). A distribuição espacial dos poliquetas sublitorais demonstrou ser nitidamente heterogênea na Baía de Guanabara. Um gradiente negativo de diversidade e biomassa foi observado em direção as partes internas e protegidas da baía. Foi encontrada uma grande área azóica dentro da baía. Por outro lado, algumas áreas com alta biomassa e baixa diversidade foram encontradas nas proximidades de locais com despejo de esgoto urbano não tratado. Nestas áreas foi observado aumento da biomassa de poliquetas no período chuvoso. Uma comunidade diversificada foi identificada na...

Factors influencing spatial patterns of molluscs in a eutrophic tropical bay

“…Mollusc diversity followed the environmental gradient, with the highest diversity in the outer sector which is most influenced by marine intrusion, and decreasing towards the inner sector, where in estuarine conditions the density and biomass increase sharply. This diversity pattern observed for molluscs also occurs in other benthic communities in GB (Lavrado et al , 2000; Van Der Ven et al , 2006; Mendes et al , 2007; Santi & Tavares, 2009), and in bays throughout the world. Although other factors are involved, community composition gradually changes according to the salinity gradient in estuarine systems (Gaston et al , 1998; Giberto et al , 2004; Giménez et al , 2006).…”

“…The distribution of benthic communities in Guanabara Bay (GB) varies significantly in space and time, whereas the spatial pattern is the most prominent. Species diversity and abundance of benthic groups (molluscs, crustaceans, polychaetes and foraminifera) differ among the areas of the bay, increasing from the inner to the outer sector as a function of the bay's gradient (Lavrado et al , 2000; Eichler et al , 2003; Mendes et al , 2004; Van der Ven et al , 2006; Santi & Tavares, 2009). Molluscs constitute one of the largest phyla of invertebrates, in both numbers of living species and numbers of individuals (Gomes et al , 2004).…”

Spatial and temporal distribution patterns of the silver mojarra Eucinostomus argenteus (Perciformes: Gerreidae) in a tropical semi‐enclosed bay

“…The species exhibits an ontogenetic change in diet: juveniles tend to be more generalist, whereas adults prey mainly on polychaetes (Kerschner et al ., ; Aguirre‐León & Yáñez‐Arancibia, ; Chaves & Otto, ). In Guanabara Bay, polychaete occurrence coincides with the area of occurrence of adult gerreids (Santi & Tavares, ). Pessanha & Araújo () investigated some ecological aspects of D .…”

Spatio-temporal sublittoral macrobenthic distribution and dominant species in Guanabara Bay, Rio de Janeiro, Brazil

“…Seasonality in Guanabara Bay bottom water is defined by two natural forces, SACW (South Atlantic Central Water) marine intrusion during the summer months, and a well-defined rainfall regime, split into dry and rainy periods (INMET, 2008;Amador, 1997;Filippo, 1997;Kjerfve et al, 1997;Valentin et al, 1999;Figure 2). SACW intrusion during the summer (November to March) gives rise to drops in temperatures (<15 °C), high dissolved oxygen, nitrate, phosphate and silicate rates, and pronounced bottom water eutrophication (Mendes et al, 2012;Petrobras 2012a, b;Santi and Tavares, 2009;Silva and Valentin, 1988;Villac et al, 1991). Hence, during this period, a temporary dry season may occur, with low rainfall throughout the bay (Filippo, 1997;Mayr et al, 1989).…”