Macrofaunal community abundance and diversity and talitrid orientation as potential indicators of ecological long-term effects of a sand-dune recovery intervention

In the last decades the increasing urban development on coastal areas have produced extensive modifications on shores all over the world, making critical the active management of pressures on sandy beaches. The use of engineering solutions to counteract beach erosion has been significantly increasing; the ecological indicators used to monitor these interventions generally focus on short- and medium-term effects, while little is known on their effectiveness on long-term temporal scales. The following ecological indicators have been tested in the present study: (a) macrofaunal community abundance and diversity and (b) orientation behaviour of Talitrus saltator, a talitrid amphipod widespread on Mediterranean and European Atlantic sandy beaches. Two sites were considered on a sandy beach of the Portuguese Atlantic coast, one located in front of a natural dune and the other at about 500 m of distance, where the dune had been rebuilt between 2000 and 2008 using geotextile tubes. In 2011 and 2012, macrofauna sampling and orientation experiments on T. saltator were performed at both sites in spring and autumn; contemporaneously the main environmental variables were registered. Macrofaunal data were analysed through multivariate statistical tests, and for the orientation distributions the circular statistics were calculated and multivariate analyses for angular data were performed. Geotextiles appeared to be successful in stabilising the recovered dunes; accordingly, the diversity of the macrofaunal communities and the orientation performances of T. saltator showed no differences between the altered and control sites. Significant reductions were nevertheless observed in the artificial-dune site regarding the abundance of T. saltator and, to a lesser extent, macrofaunal densities, likely ascribable to the presence of geotextiles instead of a vegetated natural dune, preventing invertebrates to burrow into the sand. These results, complementing a more comprehensive study on these two sites, indicate the abundance of T. saltator as the best indicator to follow long-term effects of this kind of soft-engineering intervention. The use of this bioindicator may be recommended for the late phases of monitoring procedures in dune-recovery processes.