Cordgrass canopy elicits a weak response of sediment properties and microphytobenthic abundance in a harsh environment

FIRSTATER, FAUSTO N; NARVARTE, MAITE; ALVAREZ, M FERNANDA; FANJUL, EUGENIA; IRIBARNE, OSCAR

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2016 vol. 550 p. 101 - 110

0171-8630

The magnitude of the outcome of ecosystem engineering is context-dependent, as environmental stress increases, habitat amelioration by ecosystem engineers becomes more relevant. Moreover, individual- and population-level traits of ecosystem engineers seem to affect their ability to reduce environmental stress. In Argentinean Patagonian shores (SW Atlantic, 41° S), the intertidal community is exposed to harsh conditions. We predict that in this severe environment the variation of the above-ground structure of the smooth cordgrass Spartina alterniflora, should alter the buffering of the physical stress on the substrate, through shading and reduction of wind and water flow energy, affecting the sediment properties and microphytobenthic biomass. To test this hypothesis, we experimentally manipulated Spartina density in the edge and the inner marsh both in summer and winter. In summer, evaporation and temperature were higher in clipped plots, while in winter evaporation varied across densities and location treatments, with higher water content of the sediment inside the marsh. Neither effect of Spartina density nor location were observed on sediment organic matter and chlorophyll-a concentration, while mean grain size was always smaller inside the marsh. In summer, extracellular polymeric substances (EPS) content was higher in clipped plots inside the marsh, however this was not different from the other density treatments at this location. Overall, shading had weak effects on sediment properties and microphytobenthic biomass, and most observed differences can be attributed to grain size. We speculate that harsh conditions of this system overwhelm the ecosystem engineering effects of Spartina, probably because of its relatively small aboveground biomass.