PRELIMINARY INVESTIGATIONS ON THE FLORA OF THE PERMANENT BANQUETTES IN WESTERN SICILY

The banquettes, landed clusters of dead leaves of Posidonia oceanica (L.) Delile, represent a deposited biomass from sea to land that protects the shoreline from wind and sea erosion as well as constitutes a reserve of nutrients and organic matter for sea prairies. These wracks can become a potential biodiversity hotspot as indicated by a recent investigation on invertebrates that has shown high levels of consumption of detritus (1). This biodiversity, greater than that found in coastal areas without such accumulations, can be explained by the margin effect between the marine and the terrestrial environment. The banquette can therefore be considered an ecotone (2, 3) where communities of supralittoral and inland areas coexist in the same transition system. Studies on terrestrial invertebrates of the banquettes have not shown a clear relation between the trophic beached debris and terrestrial biological communities settled on them (4). Aim of this research is to investigate the ecological role played by such accumulations in the coastline of western Sicily, with particular reference to the terrestrial plant communities that are settled on them. In western Sicily 327 km of residues were detected, 24 km of little mounds or temporary banquettes (shifted naturally by wind or storm surges) and 29 km of permanent banquettes (5). The latter are usually very rare, because beach tourism involves mechanized cleaning activities of the accumulations of dead leaves that favours the coast erosion (6, 7). In spring 2016 surveys were carried out on the flora and vegetation of permanent banquettes in the Lagoon of Marsala (Stagnone) where the largest accumulations in Sicily are found. Here were detected, in fact, more than 10 km of banquettes with a beached material layer up to about 50 meters wide, and 1 meter above the sea level. The substrate of the banquettes changes its composition depending on the distance from the shore line: near the sea it consists exclusively of organic matter, away from the coastline there is a higher sand content, with values that reach up to 33.9%. Behind the banquettes brackish marshes and rocky coasts are found. The flora occurring on the banquettes includes a low number of plants specialized for psammophilous and halophilous habitats. Near the shoreline there is a pioneer, halo-nitrophilous flora with therophytes as Cakile maritima Scop., Matthiola tricuspidata (L.) R.Br., Salsola soda L., Senecio leucanthemifolius Poir., Spergularia salina J.Presl & C.Presl, and some perennial plants as Beta vulgaris subsp. maritima (L.) Arcang. and Sonchus bulbosus (L.) N.Kilian & Greuter than can also cover large areas. Then, a belt follows where the above listed taxa are mixed with species typical of brackish marshes and nitrophilous habitats. Among them: Crithmum maritimum L., Dittrichia viscosa (L.) Greuter, Halimione portulacoides (L.) Aellen, Limbarda crithmoides (L.) Dumort., Polypogon monspeliensis (L.) Desf., Sarcocornia fruticosa (L.) A.J.Scott, Sonchus oleraceus L., and S. tenerrimus L. On the Isola Lunga the occasional presence of Calendula suffruticosa subsp. maritima (Guss.) Meikle, endemic to Sicily and Sardinia, was also observed. In fact, this taxon is associated to the coastline but linked to sandy-gravelly or rocky substrates (8). These preliminary observations have further emphasized that the ecological role of the banquettes is to be carefully evaluated in planning the coastal management in Sicily and the Mediterranean, in order to promote activities with low impact and protect these deposits, including the widening of protected areas when necessary.