Annual variation of the malacofauna on two intertidal sandy substrates with rock fragments in southeastern Brazil

Abstract

The temporal variation in molluscan communities was studied in two intertidal substrates composed of sand and rock fragments <300 mm) in São Sebastião Channel, Brazil. Samples were taken between August 1995 and July 1996 in São Francisco (mainland) and Engenho d'Água (São Sebastião Island) beaches. A pronounced decrease in abundance and diversity of molluscs was associated with changes in the structure of the environment, caused by sea storms in the beginning of the summer (December), and by the increase of waste water discharge in this same period. Areas not subjected to such events showed no evident modifications in mollusc fauna structure during the sampling period, and the small oscillations observed were attributed to population recruitment. Both natural and human factors may be acting together in determining the community organization in these environments, as is also in typical sandy beaches.<br>Estudou-se a variação anual da comunidade de moluscos em dois ambientes entremarés constituídos por areia e fragmentos rochosos <300 mm) no Canal de São Sebastião, Brasil. As amostras foram obtidas mensalmente entre agosto de 1995 e julho de 1996 nas praias São Francisco (continente) e Engenho d'Água (Ilha de São Sebastião). Uma marcante redução na abundância e diversidade foi associada às mudanças estruturais do ambiente, causada por ressacas do mar no início do verão (dezembro), e ao aumento no fluxo de esgotos domésticos neste período. Em áreas onde estes eventos não foram evidentes, não houve grande alteração na composição faunística, e as pequenas oscilações foram atribuídas ao recrutamento de populações numericamente importantes. Ambos os fatores naturais e antrópicos podem estar atuando em conjunto para determinar a organização da comunidade nestes ambientes, tal como ocorre em praias arenosas típicas

Soft-Bottom macrobenthic communities of the Vitória Bay estuarine system, South-eastern Brazil

“…It most probably escapes from low oxygen levels by closing tightly and switching its metabolism to anaerobic respiration (Constanza et al, 1993). Anomalocardia brasiliana is common in areas affected by organic pollution (Schaeffer-Novelli, 1980;Denadai et al, 2000), as observed in this study, in stations extremely polluted by sewage (e.g. station 10).…”

“…2). These and similar seasonal variations of macrofauna abundance are most probably related to reproductive cycles, as recorded for various South American sandy beaches (Souza & Gianuca, 1995;Bemvenuti, 1997;Veloso et al, 1997;Ieno & Bastida, 1998;Denadai et al, 2000). If fluctuations in larval recruitment contribute to temporal variations in abundance, the distribution and settlement of larvae are constrained by physical processes such as fine-scale hydrodynamics (Snelgrove & Butman, 1994).…”

Structure of molluscan assemblages in sheltered intertidal unconsolidated environments

“…Among the four environmental types found here, Engenho d'Água (T1) was the richest sector in the channel where no dominant species were evident. It presented a wide low-tide terrace covered with rocky fragments and was subjected to a low influence of organic pollution (Denadai et al 2000). Organic pollution influenced assemblage composition in such heterogeneous low slopping habitats (Denadai et al, 2000).…”

“…It presented a wide low-tide terrace covered with rocky fragments and was subjected to a low influence of organic pollution (Denadai et al 2000). Organic pollution influenced assemblage composition in such heterogeneous low slopping habitats (Denadai et al, 2000). In fact, the lower richness in São Francisco (28 sp.…”

The false limpet Siphonaria gigas, a simultaneous hermaphrodite, lives in pairs in rock fissures on the Pacific coast of Panama

“…At the scale of meters to centimeters, vertical zonation and distributions across habitats are largely driven by the interplay between behavioral responses to environmental stress and species interactions (Menge and Sutherland 1987;Bertness and Callaway 1994;Tomanek and Helmuth 2002). The spatial arrangement of individuals is affected by impact from waves, temperature extremes during low tides (Underwood 1980;McQuaid and Branch 1984;Denny and Wethey 2001), predation and competition (Connell 1975;Menge and Sutherland 1987;Denadai et al 2000;Turra and Denadai 2006), and social interactions including gregarious settlement (Burke 1986), territoriality (Shanks 2001), and competition for mates (Collin 1995). Here, we report habitat preferences and pair living in an intertidal invertebrate and suggest possible causes for this distinctive and highly unusual spatial pattern and mode of life.…”