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Posidonia oceanica is an endemic Mediterranean seagrass that forms wide and dense meadows from the surface up to about 40 m depth. P. oceanica can develop on matte, a typical terraced structure built up by itself, consisting of intertwined rhizomes, roots and sediment, which may allow shoots to reach the sea surface, where may form typical reefs (récif barrière) considered “natural monuments”. These structures have received increasing attention for the potential ecosystem services they provide in protecting the coasts from erosion, forming new habitats (coastal lagoons) and contributing to carbon sink. P. oceanica reefs are particularly exposed to the expected increase in temperature and to storm frequency and intensity, which represent a problem in terms of P. oceanica “natural monuments” conservation. Therefore, much more attention must be paid to the implementation of monitoring tools able to detect the early signs of seagrass regression. The main aim of this study was to investigate the distribution of the P. oceanica reefs located in front of 4 pocked beaches (PB) along both the northern and southern coasts of Sicily. A remote sensing approach was used to assess the reef extensions including their associated structures (atolls, and tiger meadows). In particular, very high-resolution drone images (~2cm of pixels size), combined with GPS field data, were used to obtain 2 and 3D-reconstruction of P. oceanica reefs. Generated orthophotos and digital elevation model were imported into geospatial analysis software to quantify their extension and volumes. The 3D-model allowed to estimate bathymetrical distribution of P. oceanica reef. This approach may enable to achieve a more detailed and complete understanding of the role of P. oceanica reefs in coastal marine dynamics and in PB in particular. This might also contribute to gain a better insight into the ecosystem services they provide.

Seagrass detritus accumulates along the coasts forming beach-cast wracks. Being subject to environmental gradients and hydrodynamism, the size and composition of beach-cast wracks may vary in space and time. Also the composition may vary depending on both proximities to and productivity of the adjacent seagrass meadows. Despite their dynamic nature, seagrass beach-casts provide important ecosystem services, by contributing to the nutrient and carbon flow between marine and terrestrial systems, supporting beach biodiversity and trophic webs and protecting the coastline from erosion. However, the knowledge about beach-cast dynamics, ecological role and functions is still fragmented and deserves a greater effort. Here, we aimed to assess the seasonal dynamics of beach-casts in terms of mass, nutrient and carbon content, and composition. The study was conducted in November 2018 and February 2019 in a Sicilian beach (Capo Feto, TP), adjacent to large nearshore Posidonia oceanica meadows. Surficial and deep (0.5-2 m) seagrass beach-cast samples were collected through a handsaw along the seaward side of the wrack, at three equidistant sites (100 m). Beach-cast mass (kg DW m coastline-1) exhibited wide temporal fluctuations, significantly decreasing from November to February, as an effect of the winter sea storms. A higher mass was also evident in the deep layer than in the surficial one only in November, suggesting a higher compactness of deep layers in the highest beach-cast wracks. Accordingly, nitrogen and organic carbon content (kg DW m coastline-1) showed the same pattern revealing a key role of the beach-cast as a nutrient source between adjacent systems. Despite the high seasonal variability, beach cast composition was rather constant over time, showing an overall dominance of seagrass detritus, and an increase in sediment in the deep layers. This indicates a relevant input from the adjacent P. oceanica meadow and confirms the role of banquette as sediment trap.

Posidonia oceanica is an endemic Mediterranean seagrass that forms wide and dense meadows from the surface to depths of about 40 m. During fall and winter, due to aging and storms, leaves and rhizomes break away from the seagrass meadows and accumulate on the shores (from a few centimeters in the water to several meters inshore) forming conspicuous beach-casts of P. oceanica detritus. These structures have received increasing attention in the last decade for the potential ecosystem services they provide in protecting the coast from erosion, linking marine and terrestrial food chains and contributing to carbon and nutrients fluxes. However, seagrass beach-cast morphology is not easy to estimate because: i) beach-casts have a complex dynamics; ii) they can reach very large extensions; iii) their shapes are not comparable with standard geometric figures. The aim of this study was to investigate the morphology and dynamics of P. oceanica beach-casts in three beaches of Sicily (Capo Feto, Maragani and Scala dei Turchi) characterized by different productivity of the nearshore meadows. A remote sensing approach was used to assess the beachcast extension, morphology, volume and derivate parameters. In particular, very high resolution drone images, combined with GPS field data, were used to obtain a 3D-reconstruction of P. oceanica beach-casts. Generated ortophotos and digital elevation model were imported into geospatial analysis software to quantify volumes and their spatial and temporal evolutions. The 3D-model allowed to accurately estimate different levels of seagrass detritus accumulation. This approach enables to achieve a more detailed and complete understanding on the role of P. oceanica detritus beach-casts in coastal marine dynamics. This might also contribute to gain a better insight into the ecosystem services they provide.

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.

Posidonia oceanica meadows are among the most important marine coastal ecosystems in the Mediterranean Sea due to several roles they are able to play. They, in fact, support high levels of primary production, enhance sedimentation of suspended particles through their canopies, prevent resuspension of marine sediments by means of roots and rhizomes and counteract coast erosion. Part of the primary production of this seagrass is not transferred to herbivores either immediately to detritus pathway but it can accumulate on the shore in form of banquette, typical structures exerting a significant role in protection of beaches from erosion. To accurately measure the extension, morphology, volume and derivate parameters of these structures a remote sensing approach is often required, since very large banquettes can occur along the shore. The aim of this study was to investigate the architecture and dynamics of some banquettes observed along coasts of Sicily, by using a multitemporal analysis of remotely sensed images. In particular very high resolution drone images, combined with GPS field data, was used to obtain a 3D reconstruction of banquette morphology. The study was carried out along three pocket beaches: Capo Feto (TP), Maragani and Scala dei Turchi (AG). Generated ortophotos and digital elevation model were imported into geospatial analysis software to quantify volumes and their spatial and temporal evolutions. 3D approach allowed us to accurately estimate different levels of necromass accumulation.This approach will allow to achieve a more detailed and complete view on the role of P. oceanica detritus stocks within coastal marine dynamics. This might also contribute to gain a better insight into the ecosystem services they provide.

Posidonia oceanica is an endemic Mediterranean seagrass that forms wide and dense meadows from the surface up to about 40 m depth. This species can develop a biogenic structure called matte, a typical terraced formation built up by itself, consisting of intertwined rhizomes, roots and sediment, which may allow shoots to reach the sea surface forming reefs (récif barrière), considered natural monuments. Posidonia oceanica reefs are particularly exposed to the ongoing increase in temperature and in storm frequency and intensity due to climate change, with negative repercussions on their conservation. Much more attention must be paid to the implementation of monitoring tools able to detect early signs of reef regression. In this study, the distribution of P. oceanica reefs located along southern coasts of Sicily (Italy, Mediterranean Sea) was investigated. A remote sensing approach was used to assess reef extension, morphological features (e.g., atolls), upper limit and occurrence of dead matte. In particular, very high-resolution drone images (~ 2 cm pixel size), combined with GPS field data, were used for 2D- and 3D-reconstruction of P. oceanica reefs. The 3D-model allowed to estimate bathymetrical distribution of P. oceanica reef enabling to achieve a more detailed and complete understanding of the P. oceanica reef architecture

La presenza di funghi endofiti in rizomi radici e foglie di Posidonia oceanica (L.) Delille è stata valutata nell’ambito di uno studio morfologico ed ecologico condotto in differenti ambienti mediterranei. In particolare, su individui prelevati in 5 diversi siti costieri siciliani, sono state effettuate osservazioni mirate alla visualizzazione di strutture miceliari nei tessuti dell’ospite, all’isolamento di colonie fungine su substrati artificiali agarizzati e alla loro identificazione su basi morfologiche e molecolari. Le indagini, sebbene tuttora in corso, rilevano la costante presenza di microrganismi fungini endofiti negli organi saggiati sia pure con differenti valori di frequenza d’isolamento. Lo studio, inoltre, ha consentito di segnalare per la prima volta Lulwoana sp., Ochroconis sp. e Xylaria sp. quali endofiti fungini in P. oceanica. Ulteriori indagini saranno rivolte alla definizione del ruolo di tali funghi nel ciclo biologico dell’ospite e, più in generale, nell’ecosistema delle praterie marine mediterranee oggetto di studio.

Posidonia oceanica is considered a key species due to its different roles as primary producer, substrate for many species, shoreline erosion protector and long-term carbon store (1).The importance of P. oceanicahas stimulated several studies aimed at quantifying its status. In particular growth performance of rhizomes has become among the most used descriptors for monitoring changes of P. oceanicameadows induced by human or naturalexogenous factors (2). However, ability to detect any change of growth in space or in time is often confounded by natural age-induced variations, which involves serious interpretation problems (3). A general approach adopted to overcome this problem is to build growth charts as reference tool for comparison purposes. Charts describing patterns of biometric features conditioned to age are increasingly used as comparison tools, even if almost exclusively in Auxology(4). Their use can be extended to other disciplines, including ecological studies, although very large data sets are required for obtaining reliable estimates and curves should be flexible enough to account for non-linear growth pattern over age (5). In this work reference growth charts involving different P. oceanicagrowth performance measures (speed of growth and primary production of rhizomes) will be presented. Curves have been built using proper statistical frameworks (GLMM, Segmented and Quantile Regressions), based on more than 13000 annualgrowth data recorded by lepidochronology (6) on about 1600 shoots collected at 4–32 m depth range along Sicilian coasts.Growth patterns exhibited distinct trends as regards the relationships with depth: neither speed of growth nor primary production of rhizomes depended on depth until 14 m, while at deeper stands significant linear decrease by 3.5–2.0% for 1 m increase in depth was observed, due to light and sedimentation reduction. The considerable size of the dataset allowed to estimate the accurate shapes of the percentile curves (from 5thto 95th), revealing non monotonic relationships of growth with respect to shoot age with an initial increase followed by an overall decrease of 40% during the following years of the explored lifespan. The accompanying model-based classification procedures presented, will allow to obtain comparable results also when age of shoots is largely different (up to 20 years) (7). The growth charts may represent a noteworthy tool for researchers involved in studying of different aspects of seagrass monitoring. It is hoped that the proposed framework will facilitate assessment of growth performance status and comparative analysis of growth data from different populations around the Mediterranean Sea