CONICET | Buscador de Institutos y Recursos Humanos

The magnitude of the outcome of ecosystem engineering is context-dependent; asenvironmental stresses increase, habitat amelioration by ecosystem engineers becomes morerelevant. Moreover, the individual- and population-level traits of ecosystem engineers can affecttheir ability to reduce environmental stress. On the Patagonian shores of Argentina (SW Atlantic,41° S), the intertidal community is exposed to harsh conditions. We predicted that in this severeenvironment, variation in the above-ground structure of the smooth cordgrass Spartina alterniflorashould buffer the physical stress on the substrate through shading and reduction of wind andwater flow energy, ultimately affecting the sediment properties and microphytobenthic biomass.To test this hypothesis, we experimentally manipulated cordgrass density at the edge and innermarsh of a S. alterniflora meadow during both summer and winter. In summer, evaporation andtemperature were higher in clipped plots, while in winter, evaporation varied across densities andlocation treatments, with higher sediment water content in the inner marsh. No effect of S. alternifloradensity or location were observed on sediment organic matter or chl a concentration, andmean sediment grain size was always smaller inside the marsh. In summer, extracellular polymericsubstance (EPS) content was higher in clipped plots inside the marsh, however this did notdiffer from the other density treatments at this location. Overall, shading had weak effects onsediment properties and microphytobenthic biomass, and most observed differences wereattributable to grain size. We speculate that the harsh conditions of this system overwhelm theecosystem engineering effects of S. alterniflora, probably because of its relatively small abovegroundbiomass.

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