Effects of rainfall changes on S. densiflora cordgrass and the habitat use by Akodon azarae in a southwestern Atlantic saltmarsh

PASCUAL, J.; CANEPUCCIA, A.; ALBERTI, J.; IRIBARNE, O.

Mar del Plata

Congreso; CERF's Inaugural International Conference of the Americas; 2012

Coastal and Estuarine Research Federation

Planetary-scale events like El Niño Southern Oscillation (ENSO) can alter rainfall patterns worldwide, with important effects on the abundance and distribution of organisms and even biological interactions. Despite the extensive evidence about the effects of ENSO on marine and terrestrial systems, ecological consequences of rainfall fluctuations in transitional communities remain poorly understood. The aim of this study was to evaluate the effects of rainfall changes on marsh use by the Pampas mice, Akodon azarae and its relationship with the cordgrass Spartina densiflora. Field surveys, in a salt marsh of the South Western Atlantic coast (Mar Chiquita coastal Lagoon 37° 45' S, 57º 23' W, Argentina), showed that the abundance of A. azarae increased during rainy summers (e.g. El Niño 2004-2005, El Niño 2006-2007), with the lowest abundance during the dry one (e.g. La Niña 2007-2008). Salt content in marsh sediments and plant tissues were negatively correlated with rainfall levels. Field experiments manipulating sediment salinity confirmed previous observations. Under salt stress conditions plant growth decreased and the proportion of senescent tissues increased. Moreover rodent abundance and the consumption of plants by them decreased. Results show that rainfall fluctuations associated with ENSO events changed the physical conditions in the marsh, decreasing the primary production and indirectly modifying the habitat use by A. azarae and its trophic relationship with S. densiflora.