Benthic responses to organic matter variation in a subtropical coastal area off SE Brazil

Abstract

Organic matter quality, expressed as the proportion of chlorophyll a (Chl a) to degraded organic material (i.e. phaeopigments), is known to influence the structure of benthic associations and plays an important role in the functioning of the ecosystem. This study investigates the vertical distribution of microbial biomass, meiofauna and macrofauna with respect to organic matter variation in Ubatuba, Brazil, a southeastern, subtropical coastal area. On three occasions, samples were collected in exposed and sheltered stations, at high and low hydrodynamic conditions. We hypothesize that benthic assemblages will have high meio‐ and macrofaunal densities and high microbial biomass at the sediment surface at the sheltered site, and lower and vertically homogeneous microbial biomass and densities of meio‐ and macrofauna are expected at the exposed site. The accumulation of fresh organic matter at the sediment surface was observed at both stations over the three sampling dates, which contributed to the higher densities of meiofauna in the first layers of the sediment column. Macrofauna followed the same trend only at the exposed station, but changes in the number of species, biodiversity and feeding groups were registered for both stations. Microbial biomass increased at the sheltered station over the three sampling dates, whereas at the exposed station, microbial biomass was nearly constant. Physical exposure did not influence organic matter loading at the sites and therefore did not affect overall structure of benthic assemblages, which negates our original hypothesis. Most of the benthic system components reacted to organic matter quality and quantity, but relationships between different‐sized organisms (i.e. competition and/or predation) may explain the unchanged microbial profiles at the exposed site and homogeneous vertical distribution of macrofauna at the sheltered site. In conclusion, the high quality of organic matter was a crucial factor in sustaining and regulating the benthic system, but coupled results showed that interactions between micro‐, meio‐ and macrofauna can be highly complex.

Effects of coastal upwelling on the structure of macrofaunal communities in SE Brazil

“…strong S-SE waves, 4-6 times per month) in the period without SACW upwelling. These resuspension events can also increase water column nutrient levels, stimulate primary productivity and influence the depth distribution of organic matter into the sediments (Aidar et al, 1993;Gaeta et al, 1999;Quintana et al, 2010;Galluci and Netto, 2004). The physical disturbance level and potential for sediment resuspension in Ubatuba bays are determined by the shape of the shoreline and the orientation to the open sea (Burone et al, 2003;Mahiques et al, 1998).…”

“…Other important coastal upwelling zones in the eastern boundary Pacific and Atlantic Oceans are extremely productive and phytoplankton biomass reaches levels up to 5-fold higher compared to those in SE Brazil (Chavez and Messié, 2009;Pennington et al, 2006). Much is known about how increased primary productivity affects benthic fauna in high-productive upwelling areas (Levin et al, 2009), but limited information is available on the ecological community structure of benthic macrofauna in less productive upwelling systems along SE Brazilian coasts (Quintana et al, 2010;Venturini et al, 2011). This study investigates the effects of a seasonal upwelling on the availability of labile organic matter (i.e.…”

Efeitos da acidificação dos oceanos nos processos biogeoquímicos em sedimentos costeiros: experimentos in situ e em laboratório

“…Enquanto muitos parâmetros sedimentares podem ser definidos por estes dois elementos básicos, informações adicionais sobre a microestrutura sedimentar são necessárias para se compreender as propriedades físicas e mecânicas dos sedimentos, assim como os processos de transporte que afetam a concentração de solutos presentes na água intersticial (Burdige, 2006 (Mahiques et al, 1998). Além dos eventos de ressuspensão, já reportados na região como responsáveis por lavar a superfície do sedimento (Quintana et al, 2010;Rodrigues Alves et al, 2014). Os padrões da concentração de clorofila--a em relação à profundidade da coluna sedimentar resultam principalmente do balanço entre suprimento, transporte interno e decomposição de matéria orgânica (Sun et al, 1991).…”

“…Os padrões da concentração de clorofila--a em relação à profundidade da coluna sedimentar resultam principalmente do balanço entre suprimento, transporte interno e decomposição de matéria orgânica (Sun et al, 1991). A clorofila--a mostrou um perfil típico de sedimento costeiro e corroborável com outros estudos na região (Sumida et al, 2005;Quintana et al, 2010; …”

Remineralização da matéria orgânica sedimentar em resposta à simulação de processos oceanográficos

“…O principal objetivo é tentar compreender e expandir o conhecimento sobre os processos naturais (Fraser & Keddy, 1997 (Machado & Knoopers, 1988;Knoopers et al, 1996;Niencheski & Jahnke, 2002;Fonseca, 2004;Zarzur, 2007), regiões estuarinas Coelho (2011) e para a avaliação da influência de cultivos de organismos (Nazário et al, 2005;Freitas et al, 2008). (Quintana et al, 2008(Quintana et al, , 2010. Além disso, a presença de microfitobentos, que acarreta em maiores concentrações de clorofila-a pode ter uma influência maior, já que vai diminuindo em maiores profundidades, na plataforma externa (Alves, 2009).…”