CONICET | Buscador de Institutos y Recursos Humanos

ABSTRACT: Changes in rainfall patterns caused by anthropogenic global climate change orplanetary-scale events, such as the El Niño Southern Oscillation, can significantly affect the abundanceand distribution of organisms. Despite the evidence of such effects on marine and terrestrialsystems, ecological consequences of rainfall fluctuations in coastal marine ecosystems remainpoorly understood. Here we evaluate the effects of rainfall intensity on the interaction betweenthe cordgrass Spartina densiflora and Azara?s grass mouse Akodon azarae in a southwesternAtlantic salt marsh (Mar Chiquita coastal lagoon, Argentina). Field surveys showed that the abundanceof A. azarae increased during rainy summers (i.e. El Niño 2005 and 2007) and had lowestvalues during dry summers (i.e. La Niña 2008). Salt content in sediment and plant tissue were negativelyrelated with rainfall. In addition, field experiments showed that increased sediment salinityresulted in increased salt content in plant tissues. Elevated soil salinity also increased the proportionof senescent S. densiflora tissues and reduced plant growth. The consumption of S. densifloraleaves by A. azarae also decreased with increased soil salinity. The proportion of S. densiflora infeces collected during the driest summer was very small. Therefore, changes in the abundance ofA. azarae could be mediated by plant−rodent trophic interaction or by plant cover changes. Inconclusion, rainfall fluctuations changed the abiotic environment (i.e. salinity), decreasingprimary production and indirectly modifying habitat use by the omnivore A. azarae and its trophicinteraction with S. densiflora. The present study provides evidence that rainfall can modify ecologicalprocesses that affect the structure and dynamics of coastal marine ecosystems.

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