6533b836fe1ef96bd12a0e65

RESEARCH PRODUCT

Quali-quantitative assessment of Posidonia oceanica detritus accumulations in pocket-beaches with different productivity levels of nearshore seagrass meadows

subject

description

Posidonia oceanica detritus accumulates in late summer-autumn along the coasts forming beach-cast seagrass wracks known as banquette. Although seagrass wracks are highly variable at both spatial and temporal scales, they have an important ecological role as they protect the coast from erosion, support beach biodiversity and trophic webs and supply nutrients to dune vegetation. Previous studies have focused mainly on the beach-cast morphological characterization and variability, as well as on associated biotic communities. However, few studies have focused on the quali-quantitative assessment of seagrass wracks. The aim of this study was to assess the spatial variability of the P.oceanica beach-cast wrack, in terms of biomass and composition, in relation to productivity of the nearshore meadows. We hypothesize that highly productive seagrass meadows sustain beach-cast characterised by a greater vegetal biomass to sediment ratios than low productivity meadows. This study was conducted in November 2018 in three Sicilian pocket-beaches with different levels of productivity of the nearshore meadows: high (Capo Feto, TP), medium (Maragani, AG) and low productivity (Scala dei Turchi, AG). At each site, samples of beach-cast wracks were collected and dry biomass (kg DW m-3) and the percentage composition of the main components (leaf detritus, fresh leaves, rhizomes, aegagropilae, sediment) were estimated. Preliminary results showed a high intra-site variability and no significant differences in biomass per unit volume among the beaches with different levels of seagrass productivity. However leaf detritus represented the main component of the wrack in the beach sustained by high seagrass productivity, followed by rhizomes, while sediment component increased in the other productivity levels. Next steps will relate biomass data to the total volume of beach-cast in order to estimate the global biomass accumulated on the beach. In addition, in order to evaluate the temporal dynamics of the P. oceanica beach-cast wrack, sampling will be repeated in the same sites every three months in 2019 and will allow to complete the preliminary picture here presented.