Temporal changes in macrofauna as response indicator to potential human pressures on sandy beaches

Sandy beaches are natural dynamic ecosystems, which are becoming worldwide increasingly disturbed by intensive human direct use, coastal development and erosive evolution. In this study, we have examined whether ten years of potential increased human pressures have resulted in significant changes in the macrofaunal assemblages' structure and composition of two mesotidal sandy beaches (Cabedelo - urban beach, and Quiaios - rural beach) on the European Atlantic coast (Portugal). Seasonal macrofauna collections were performed at both beaches in two different periods, one in 1999-2000 and another in 2010-2011. The physical variables did not change significantly in both beaches throughout the studied periods, however, the urban beach was subject to an increase of human pressures (tourism and shoreline modifications) over the 10-years interval considered when compared with the rural beach. The univariate community descriptors (total density, species richness and diversity) did not differ significantly among periods for the rural beach. In contrast, temporal differences were found at the most urbanised beach, principally regarding the abundances of the amphipod Talitrus saltator and the isopod Tylos europaeus, two of the most abundant species at both beaches. PERMANOVA tests enhanced these temporal variations and the SIMPER analysis attributed to these species the main differences found between periods in this beach. Since the physical environment was similar in both periods, the ecological changes were most likely attributed to the increased human pressures observed at the urban beach. Nevertheless, this study highlights the need of further robust and effective impact assessments and long-term studies to better discern between natural and human induced changes on sandy beaches.