Microbenthos in a hypersaline tidal lagoon: factors affecting microhabitat, community structure and mass exchange at the sediment-water interface

Abstract

Three benthic microbial communities from a hypersaline lagoon with tidal influence were studied: a compact microbial mat, a 'fluffy' microbial mat and a non-cohesive diatom-dominated sediment. In each community, qualitative and quantitative analyses of phototrophs, meio- and macro- fauna were done. Vertical profiles of oxygen, sulfide and pH were measured at the sediment-water interface using microelectrodes. Physico-chemical properties of the water column were also assessed. The most compact mat, dominated by Microcoleus chthonoplastes, had the highest photo- synthetic biomass, while meio- and macrofauna were nearly absent. The compact mat showed the steepest physico-chemical microgradients and the highest fluxes of oxygen and sulfide. The 'fluffy' mat had an areal amount of chl a similar to the compact mat and contained a higher abundance of meiofauna. This mat showed the deepest oxic layer. The diatom-dominated sediment comprised a high abundance of macrofauna, but meiofauna were very scarce. This community presented rela- tively smoother microgradients and intermediate values of internal fluxes of oxygen. Our results show the close relationship between the structure of the microbenthic communities, net metabolism, and the exchange of mass at the water-sediment interface. Changes in biotic and abiotic factors determined the spatial distribution of each microbial community.