STUDIO DELLE COMUNITÀ MACROZOOBENTONICHE DELLA ZONA INTERTIDALE DI DUE SITI LUNGO LA COSTA ADRIATICA

The benthic macrofauna living in soft substrates is a biodiverse and complex community of organisms, playing a pivotal role in different contexts. Despite this, there is an increasing pressure on shoreline due to several anthropogenic activities, that has been causing degradation of coastal habitats and loss of ecosystem services. Macrofauna living in the intertidal zone can be particularly vulnerable to the alteration of natural beach dynamics, affecting the ecological traits of these organisms and overall functioning of beach ecosystem. In the Northern and Central Adriatic Sea, breakwater barriers are structures widespread all along the coastline, with the aim of increasing coastal protection and minimizing shoreline erosion by waves and currents. Breakwaters can cause alterations in hydrodynamic conditions and sediment transport, in turn responsible of changes in the soft-bottom communities. Studies on the effects of breakwater barriers on the macrobenthic community are scant and there is currently no study comparing a beach with breakwater barriers to a natural one without them regarding macrobenthos of soft substrates. Aim of the current study is to contribute filling this knowledge gap comparing macrozoobenthic communities of sandy beaches in sites with and without breakwater barriers. To test our hypotheses, two sites along the North-Central Adriatic Sea have been chosen: a natural beach with dunes (Torre Cerrano), protected by legislation, and a touristic beach with breakwater barriers and many facilities (Palombina). Monthly samplings have been carried out from February 2019 to January 2020, setting up 3 transects from the low tide level towards the high tide one in the intertidal zone. Cores of sediment have been collected from each transect and then processed and analysed to obtain the granulometry, the macrobenthic fraction, the forams, the non living component and the amount of shells. Also, the beach wrack has been analyzed in February, October and November. The M-AMBI has been applied to monthly data of macrobenthos using the AZTI Marine Biotic Index software. The results showed how the total abundance of macrofauna was statistically different in both the sites in each transect over the year. The total abundance of macrofauna all year round between transects in the same site was instead not statistically different, except for some months, like the differences between correspondent transects in the two sites. Trampling in Palombina beach could stimulate the emersion of Tritia neritea gastropod, found with high abundances in August only in this site. The tubicolous polychaete Scolelepis sp. was completely absent in Palombina in June and July, probably for its sensitivity to trampling, while in December no polychaetes were present in the same site, probably due to the anthropic disturbance caused by bulldozers. A variation in the beach profile in both the beaches occurred over the year, together with a change in the ratios between the different granulometric classes. The beach wrack composition varied between the two sites and in the same beach in the three months considered. During winter, the effects of beach erosion was sharper in Palombina, likely emphasised by breakwater barriers, together with natural erosion by sea storms and sand removal by humans. A partial overlap between the storm dates and the amount of shells was recognizable, likely due to the high water motion. M-AMBI labelled both the beaches as “high or good quality”, even if it showed not to be a good indicator to define the beach status as a whole. Insights on the composition of macrozoobenthic communities from beaches with and without breakwaters and subject to different anthropic pressures have been provided; the effect of anthropic disturbance on some organisms have been seen, together with the influence of breakwaters on sand composition and their low efficacy in protecting the coast by erosion in case of severe sea storms.