Variability of benthic assemblages in relation to the hydrological pattern in Mediterranean salt marshes (Emporda wetlands, NE Iberian Peninsula)

Abstract

The structure and composition of benthic assemblages (organisms > 100 μm) and the main factors which control them were studied in the coastal basins of the Emporda wetlands (NE Iberian Peninsula). Five coastal basins were sampled in three different conditions during one hydroperiod (1997-1998): (1) one month after the main autumnal inundation when the water level was high; (2) in the middle of the hydroperiod; and (3) when the basins were close to desiccation. Based on the hydrological pattern, three types of basins were distinguished: non-disturbed permanent waters (type 1), non-disturbed temporary waters (type 2), and disturbed temporary waters (type 3). These three types are in agreement with the classification result from the benthic assemblage composition. The type 1 basins, where more stable environmental conditions were found, had an assemblage characterised by a high density of individuals, total biomass and diversity. The assemblage of type 2 basins had lower richness and diversity values with little temporal variability. The high frequency of freshwater inputs in type 3 basins causes a high taxonomic singularity and high temporal variability of species richness and diversity. The main environmental parameters (salinity, sand percentage, total phosphorus from the sediment, and total organic carbon from the water) related to the structure of benthic assemblages, also discriminating three groups, were coincident with the three types derived from distinct hydrological patterns. Thus, water regime summarises the physical factors which ultimately determine benthic fauna.