Factors mediating the effects of an invasive reef forming polychaete on macroalgae in a Southwest Atlantic coastal lagoon.

BAZTERRICA, MARÍA CIELO; ALVAREZ, M FERNANDA; BRUSCHETTI, CARLOS MARTÍN; HIDALGO, FERNANDO JOSÉ; FANJUL, MARÍA EUGENIA; IRIBARNE, OSCAR; BOTTO, FLORENCIA

Mar del Plata

Conferencia; CERF 2012. The Changing Coastal and Estuarine Environment: A Comparative Approach.; 2012

Biological invasions are a primary research topic because its impact on the status and conservation of natural ecosystems worldwide, with large impact on coastal ecosystems, including estuaries and coastal lagoons. In the SW Atlantic Mar Chiquita coastal lagoon (37° 40´S, 57° 23°W, Argentina) the invasive reef building polychaete Ficopomatus enigmaticus can directly and indirectly change the composition and abundance of primary producers by providing reef habitat to some species and excluding others. The magnitude of these effects could be, in addition, regulated by herbivores and nutrients availability. Here we evaluate the relative importance of consumers (large consumers: birds, fish and crabs; small consumers: amphipods, hydrobiid snails and crabs) and nutrients in controlling macroalgae development on reefs and on the sediment in areas without reefs. Exclusion experiments showed that large consumers positively affect green macroalgae development in sediment without reefs, probably by enhancing availability of bivalve shells for macroalgaeattachment, but had no effects on red and green macroalgae development on the reefs. Macroalgae incubation under nutrient addition and small consumer exclusions showed that nutrient had not effects on macroalgal biomass and small consumers negatively affect the development of the green alga Cladophora sp. probably by direct consumption but had a positive effect on the red alga Polysiphonia subtilissima biomass. These interactions would determine the abundance ofmacroalgae but also the state of algal mats (e.g., thallus damage) and environmental heterogeneity (e.g., algal covered or bare patches) of the coastal lagoon. Consequently, the effect of other community structuring forces on the effects of invading ecosystem engineer need to be included in the understanding of the invasions processes as a tool to understand the processes changing coastal and estuarine enviroments.