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Salt marshes are regarded as among the most productive coastal ecosystems, important “blue carbon” sinks and a support for benthic communities with large abundances, whose structure may be strongly influenced by salt marsh vegetation. During the last few decades, Spartina alterniflora has been colonizing bare mudflats in the Bahía Blanca estuary, and a large increase in the area covered by salt marshes has been reported. This colonization can strongly influence the structure of benthic fauna and its role in the carbon cycle. The hypothesis of this study was that the community structure and the organic carbon contained in the meio- and macrobenthos change between tidal flats and salt marshes recently colonized by S. alterniflora. Response variables studied to compare the tidal flat and salt marsh were density, biomass and production to biomass (P/B) ratio of macro- and meiobenthos. Density and biomass of Gastropoda and P/B ratio of Nematoda were higher on the salt marsh than on the tidal flat. By contrast, density and biomass of Polychaeta were higher on the tidal flat. These results suggest that the expansion of S. alterniflora marshes on tidal flats produces changes in the structure of the macro- and meiobenthos community (taxonomic composition and biomass) that have an influence on carbon cycling.

El objetivo de este trabajo fue evaluar las características ópticas y los parámetros físicos y químicos para determinar las zonas en las lagunas de Sauce Grande y Chasicó (Provincia de Buenos Aires). Se usó un espectrorradiómetro portátil para obtener los espectros de reflectancia. Las mediciones se realizaron en febrero de 2010. Los valores de clorofila a se obtuvieron en el laboratorio a partir de muestras de agua oobtenidas en superficie. Se utilizó una sonda multiparamétrica para obtener los parámetros in situ. La transparencia del agua se estimó utilizando un disco Secchi. Como resultado del análisis estadístico por la firma espectral del agua, se obtuvieron 3 zonas en cada lago. En la laguna Chasicó, la zona 1 representaba la zona centro-sur del lago; la zona 2 coincidió con la NW en el lago, mientras que la zona 3 se relacionó con la desembocadura del río Chasicó. En el lago poco profundo de Sauce Grande, las subzonas representaban: el área NNE en el lago (zona 1); E y SE del cuerpo de agua (zona 2) y la desembocadura del río Sauce Grande (zona 3). La profundidad máxima en el lago Chasicó fue de 9 m, mientras que en la salsa Sauce Grande fue de 1,50 m. Como consecuencia, los valores de reflectancia en el ambiente poco profundo de Sauce Grande superaron el 8% y en el lago Chasicó los valores de reflectancia no superaron el 6%. Aunque ambos cuerpos de agua son poco profundos, el efecto desde el fondo fue más evidente en Sauce Grande que en Chasicó.

The development of the phytoplankton winter bloom and the accumulation of particulate suspended matter (PSM) inside sediment collectors were assessed in the inner zone of the Bahía Blanca Estuary. The phytoplankton bloom (chlorophyll up to 25 μg l−1 and abundance up to 8 × 106 cells l−1) was related with high levels of dissolved inorganic nutrients and underwater light availability (Im up to 355 μE m−2 s−1) and was dominated by relatively small diatoms, e.g. Chaetoceros sp.1 (3–8 μm). Conversely, large planktonic diatoms, mostly Thalassiosira spp. 20–60 μm, were found in the accumulated material inside the collectors, together with benthic microalgae and high concentrations of chlorophyll, phaeopigments, particulate organic matter (POM between 18 and 32% of total PSM) and C:N ratios >12. The composition of the settled material indicated vertical exportation of phytoplankton to the benthos, external loads of detritus and bottom resuspension. The present study highlights the close benthic‐pelagic interactions in shallow coastal environments characterized by high productivity.