Variable responses of ecosystem functions to changes in benthic microalgae induced by nutrients and herbivorous snails

ALBERTI, J.; CEBRIAN, J.; ALVAREZ, F.; ESCAPA, M.; ESQUIUS, K.S.; FANJUL, E.; SPARKS, E.; MORTAZAVI, B.; IRIBARNE, O.

Mar del Plata

Congreso; IV Congreso Internacional de Servicios Ecosistémicos en los Neotrópicos: de la investigación a la acción; 2015

A great effort has been made to identify factors that regulate community structure and their consequences on ecosystem functions. Nutrients and herbivores are now well known drivers of plant species abundances and assemblages, and their effects on ecosystem functions through changes in biodiversity have been recently explored mostly on artificial plant communities. We used estuarine microphytobenthic communities as a study system to evaluate the effects of herbivores and nutrients on primary producers, and also, on some ecosystem functions. We performed a factorial experiment manipulating nutrients (N and P) and grazers (Heleobia australis, snails) on one tidal flat at the Mar Chiquita coastal lagoon (Argentina). We found strong impacts of snails and weak effects of nutrients on the abundance, diversity and assemblage of benthic microalgae, but the effect on ecosystem functions was more variable: N2-fixation was only affected by nutrient addition, organic matter and water content were only affected by snail grazing, denitrification by the interaction between both factors, and EPS (as a proxy for sediment cohesiveness) was not affected. Overall, this study reveals that external drivers can have profound impacts on the abundance and assemblages of primary producers, that are not necessarily translated to a wide range of ecosystem functions.