Relationship between invertebrate traits and lateral environmental gradients in a Mediterranean river-floodplain

The aim of the present Study was to describe the relationships between macroinvertebrate traits and lateral hydrological and environmental gradients in a Mediterranean river-floodplain, from the main river channel to three disconnected floodplain wetlands. Bimonthly water and macroinvertebrate samples were collected from ail array of riverine wetlands in the Ebro River in northeast Spain. Our analysis of trait structures in wetlands aligned along a lateral hydrological gradient showed that community composition changed from a rich and abundant invertebrate community dominated by generalist species adapted to disturbance at the river site to a more trait-diversified community of specialist species adapted to stability and biotic interaction in hydrologically disconnected floodplain sites. The diversity Of functional groups peaked at intermediate-connected sites, where both generalist and specialist species coexist. The highest richness of functional groups was found in the river site, reflecting its highest habitat heterogeneity. The main environmental variables shaping the structure of invertebrate traits extracted after Redundancy Analysis were flood duration and frequency (surrogates of hydrological disturbance), dissolved solids (surrogate of confinement) and nitrate concentration (surrogate of agricultural pressure). These environmental variables explained 43 % of the existing variability in invertebrate traits. Because groups with similar traits responded in different ways to the main gradients, we conclude that the functional grouping of invertebrates provides ail adequate and simple tool to assess changes in functionality and the effect of lateral gradients across a floodplain. Our results highlight the need to integrate the Study of rivers and their floodplains to better account for their close interaction.