Characterization of Argentinean salt marsh Spartina wracks and their effects on sediment and associated biota

MONTEMAYOR D.; FARINA, J.; CANEPUCCIA, A.; ADDINO M.; VALIÑAS M.; IRIBARNE O.

Congreso; CERF; 2012

The aim of this study was to evaluate, at a regional scale, the patterns of Spartina wrack distribution, dynamics and composition in South West Atlantic salt marshes (San Clemente 36º 19’S, Bahía Blanca 38º 59’S, Bahía Anegada 40º 19’S, mouth of Río Negro river 41º 01’S and Bahía San Antonio 40 44’S) and their effects on the soil condition and biota. Field samplings revealed that the marsh height zone with larger amount of wrack cover in all the studied marshes was the land-marsh limit. We also found that wrack detritus species composition depends largely on each marsh standing biomass assemblage (i.e. if dominated by Spartina alterniflora or S. densiflora) but  likely also by the marsh geomorphology. The biomass wrack changed along the sampling dates (spring, summer and autumn) but without seasonal trends. Through a field experiment comparing wrack and bare zones we found that wracks in the land-marsh limit ameliorated extreme temperatures and in some occasions increased soil humidity, while no effects were found for sediment organic matter content. They also increased the number of individuals, the number of species and the diversity index for soil biota. In conclusion wracks have important effects in the microclimatic conditions of the soil as well as in the soil biota assemblage. Taking into consideration the latter, and that they are a widely distributed disturbance in SW Atlantics marshes, all evidences suggest that wracks plays an important role in the structuring of salt marshes soil biotic assemblage.