Benthic-pelagic coupling in intertidal mudflats of the Bahía Blanca estuary.

ZAPPERI, G.; PRATOLONGO, P.; MAZZON, C.; PIOVÁN, M.J.; MARCOVECCHIO, J.

Mar del Plata

Conferencia; CERF 2012-The changing coastal and estuarine environment: a comparative approach; 2012

Coastal and Estuarine Research federation

The benthic-pelagic material exchange is of crucial importance for the functioning of coastal ecosystems. In the intertidal mudflats of the inner Canal Principal, a part of the Bahía Blanca Estuary (Argentina) we defined two different subsystems according to habitat nature and the composition of benthic communities. Crab beds occupy the higher elevations within the intertidal zone, present steep slopes and the burrowing crab Neohelice granulata dominates benthic communities. Laeonereis flats occupy plain areas at lower elevations, present low crab burrows density, and benthic communities dominated by the polychaete Laeonereis acuta. On a seasonal basis, 7 sediment cores were collected from each subsystem and dark microcosm incubations were carried out in the laboratory. Microcosms consisted of PVC cores containing 15 cm of sediments and XX cm of overlying water, collected from the study site. Water samples for analysis were taken at the start and after 4 hours of incubation. Dissolved inorganic nitrogen (DIN= ammonium + nitrate + nitrite) and phosphate concentrations were used to estimate flux rates. After incubations, sediments were sieved (0.5 mm mesh) and macrofaunal individuals identified. Results obtained after a complete year of measurements revealed a peak of crab activity during late summer, which was out of phase with the winter peak on Laeonereis flats. Peaks of benthic activity closely related to suspended solids concentrations in the water column, being higher crab activity associated to higher turbidity, and higher polychate densities to higher transparency. Both subsystems performed as sources of DIN during most of the year except in autumn, when flux rates reversed. This pattern was related to the chlorophyll content in surface sediments, suggesting a strong influence of microphytobenthos on DIN uptake. Both subsystems behaved as sinks for phosphate through the year, and the uptake rates were related to the initial concentrations in the water column