Bioturbation in a pristine salt marsh ecosystem of Patagonia (Caleta Valdes)

FRANCO M.; FERRANDO A.; MONOURY E.; STORA G.; COMMENDATORE M.G.; CUNY P.; NIEVAS M.; GONZALEZ E.D.; ESTEVES J.L.; GILBERT F.

Congreso; 2da Reunión Argentina de Geoquímica de la Superficie; 2012

Universidad Nacional del Sur- CONICET

Nutrients and contaminants cycles in marine intertidal zones are significantly influenced by sediment mixing that depends on both environmental conditions (current, tides, winds) and biological processes by macro-organisms (i.e. bioturbation). The present work specifically aims to seasonally investigate the bioturbation processes in Caleta Valdes, a pristine ecosystem inside the Natural World Heritage Valdes Peninsula. To do so, four PVC corers (110 mm diameter, 250 mm deep) were inserted in the sediments at the study site (in-situ experiment). In parallel, four other cores were sampled and then incubated at the laboratory in aerated water and in situ temperature (ex-situ experiment). Then, inert UV-detectable particles (luminophores) of two different size ranges were added at the surface of in-situ and ex-situ sediments. After two weeks, the cores were sliced and the luminophores, macrofauna and organic matter (OM) distribution analyzed in each layer. After subsampling for OM analysis, the different layers were sieved (0.5 mm mesh) to separate the macrofauna, which was fixed in formalin, and sediments. Then, sediment luminophore content was measured using a fluorescence microplate reader and bioturbation quantification realized for each core with a specific numerical model (François et al., 2002). Bioturbation was shown to be independent of both luminophore size and type of experiment. Results obtained so far in Autumn and Winter demonstrated no seasonal difference in the superficial bioturbation (biodiffusive coefficient Db). On the other hand, the intensity of deeper bioturbation (bio-advective coefficient r) was more important in Autumn than in Winter. This global difference in biological sediment reworking could be explained by a reduced activity and/or by changes in the macrobenthic community structure in Winter (analysis in progress).This seasonal survey will allow us to understand the dynamics of the macrobenthic structure and functioning in Caleta Valdés. Next step will be to evaluate the response of this community to an experimental hydrocarbon contamination.