The functional composition of the benthic invertebrate community of the Mondego estuary : insights within the functioning of this ecosystem

Abstract

The main aim of this study was to investigate the functional composition of the subtidal benthic invertebrate communities of the Mondego estuary and thus contributing to a better understanding of the response of these communities to the pressures within this type of ecosystem. We characterized the environmental conditions and investigated the spatial and seasonal distribution of the communities by means of traditional taxonomic analysis and BTA. Moreover, we investigated the relation between taxonomic and functional composition by comparing indices of taxonomic and functional diversity. Traditional taxonomic analysis highlighted spatial and seasonal variations of community composition (i.e., a general reduction of species richness, Shannon-Wiener diversity, and an increase of species density towards the upper parts of the estuary). BTA analysis highlighted the functional characteristics of the benthic community within the estuary and common features across species that have appeared or disappeared among seasons. Furthermore, BTA allowed to investigate interactions among traits (i.e., the strong influence of the trait ‘salinity preference’) and was used to calculate functional diversity (FD). Indices of taxonomic diversity (Shannon-Wiener index) and FD (RQE index) allowed to explore the relation between taxonomic and functional composition. This relation might potentially have indicated that the community at the upper most reaches of the estuary exhibits lower functional redundancy than the downstream assemblages. This study represents one of the first attempts to investigate the functional composition of the benthic invertebrate community in an estuarine environment by means of BTA. BTA in addition to traditional taxonomic analysis provided a more comprehensive understanding of the functioning of this ecosystem. Therefore, the inclusion of BTA is highly recommendable for estuarine ecological studies, but more research is needed to improve its effectiveness regarding the following issues: (i) the set of selected biological traits should be optimized towards the inclusion of more relevant ecological information. This objective can be achieved by improving the knowledge on single species biological traits, which is at present still fragmentary; (ii) the biological traits of species should be linked with the services these environments provide. This traitservice association will be a crucial step in ecosystem service monitoring and management.