Gulf Of Oristano Research Articles

Marine soundscape and its temporal acoustic characterisation in the Gulf of Oristano, Sardinia (Western Mediterranean Sea)

The soundscape of the marine environment is a combination of geophony, biophony and anthropophony. Here, the soundscape of the Gulf of Oristano, a shallow inlet on the western coast of Sardinia including a special conservation area (Habitat Directive) and a national marine protected area, was investigated. Data collection was performed during July 2019, November 2019 and May 2020 using underwater acoustic equipment. The goal of this study was to characterise the ambient sound levels (Sound Pressure Level dB re 1 μPa) and describe the main soundscape components. The soundscape exhibited significant circadian and seasonal variations: the lowest and highest median SPL values were observed in the Spring (120–140 dB re 1 μPa; post-COVID-19 pandemic lockdown) and the Summer (128–150 dB re 1 μPa) respectively. Biophony was identified and characterised as dolphins’ ‘clicks’ and crustaceans’ ‘snapping’. Shrimp activity was dominant in the summer, while dolphin passages were observed across all sampling periods, accounting for 46.4% of the total recordings. Anthropophony, namely vessel passages, was predominant in the summer during the day-time and represented up to 42% of the acoustic space in the low-frequency band. Geophony increased low-frequency noise, and represented a highly variable component of the local soundscape. The marine soundscape is a valuabletool for defining integrated management plans for marine ecosystems, allowing the assessment of habitat quality, characterisation of sound sources and evaluation of the impact of anthropogenic activities.

Joint use of biological traits, diversity and biotic indices to assess the ecological quality status of a Mediterranean transitional system

In the present study, we tested the effectiveness of biological trait analysis (BTA) as an ecological indicator in support of the assessment of the Ecological Quality Status (EQS) of a Mediterranean transitional system by commonly used macrobenthic assemblage diversity (e.g. H’ and Margalef) and biotic (BENTIX, M−AMBI and M−bAMBI) indices. Ten biological traits describing morphological, behavioral and life history characteristics were considered for the analysis of the functional structure of macrobenthos. As a test study, a historical dataset obtained from the Cabras lagoon (Sardinia, Italy) comprising a riverine site, the lagoonal main body, a confined pond, a seaward creek and a marine channel connected to the Gulf of Oristano was analyzed. Our results showed clear spatial changes in macrobenthic density, number of species and diversity indices along the riverine-lagoon-sea gradient, which were well reflected in the EQS values based on M−AMBI and to a lesser extent on M−bAMBI. The abundance-based functional diversity was significantly related to the structure and taxonomic diversity of the benthic community. Similarly, the Community-level Weighted Mean test computed with abundance data, rather than with biomass data, supported major evidence for differences in the ecological conditions of the different study sites. In particular, all riverine, lagoonal and confined stations had poor or bad EQS, indicating unstable and warning conditions in this Mediterranean transitional water body. Overall, the BTA approach appeared to be a very promising method in reporting the expected environmental and biotic variability in the Cabras lagoon system and in supporting the EQS assessment by M−AMBI. We conclude that an in-depth knowledge of the benthic communities in terms of both taxonomic and functional aspects is an indispensable basic tool for understanding the variability of the brackish-water systems and for properly assessing their environmental quality.

Evolution of a single incised valley related to inherited geology, sea level rise and climate changes during the Holocene (Tirso river, Sardinia, western Mediterranean Sea)

We performed a morpho-stratigraphic study of the Tirso River incised valley (Sardinia Island, western Mediterranean Sea), an erosional feature crossing the Sinis fault, a major normal fault bordering the Campidano basin between the Gulf of Oristano and the western Sardinia shelf. High-resolution seismic reflection profiles and multibeam echosounder data, integrated by age-constrained stratigraphic logs derived from 9 sediment cores enabled us to reconstruct the valley evolution during the Holocene. We found that the Tirso valley is the result of a single event of incision and infill during the last eustatic cycle, strongly controlled by the presence of the Sinis fault. In fact, this structure represents a geological threshold that marks an abrupt change in substrate lithology and seabed slope, which controlled the valley morphology, narrow when downcutting early Pliocene formations along the steeper open shelf, and wider inside the Gulf, in the Pleistocene alluvial deposits of the flatter Gulf of Oristano. The sedimentary record starts with alluvial sediments filling the valley along the shelf during the initial phase of sea level rise, i.e., over 10 ka. During the last ~9.0 ka, a bay head delta developed, with the formation of barriers at the gulf entrance. In the mid-late Holocene, the progressive sea-level rise led to rapid drowning of the barrier system, recorded by marine and estuarine sediments filling the valley. Analysis of ecological associations in the cores, collected along a valley-normal transect, allowed for a detailed reconstruction of the paleo-environmental conditions during the latest phase of the incised valley filling controlled by global climatic variations in the Mediterranean region between ~9.0 and ~ 4.5 ka. Together with eustasy, our work reveals that the evolution and sedimentary infill of the Tirso incised valley was strongly controlled by inherited geological constraints, which influenced the morphology of the valley and the stratigraphic pattern.

Massive stranding event revealed the occurrence of an overlooked and ecosystem engineer sponge

Climate change is increasing the frequency, magnitude, and socio-economic costs of unprecedented extreme weather events and disasters. An exceptional stranding event of benthic species, mainly represented by the ecosystem engineer Porifera (Demospongiae) Geodia cydonium (Linnaeus, 1767) was observed in the Gulf of Oristano (Sardinia, Italy, Western Mediterranean) in 2018 after an extreme meteorological event. The stranding phenomenon was assessed and quantified by means of quadrats sampled along the beach highlighting all the conspicuous species; the benthic sponge community in the area was evaluated through underwater SCUBA transects. Stranding reached density peaks of up to 0.88 ind m−2, and the most abundant species reported was the sponge G. cydonium, followed by molluscs, bryozoans, a rare teleost fish, and many other species. The putative source populations were identified in quite shallow (less than 2.5-m depth) Posidonia oceanica (Linnaeus) Delile, 1813 meadows, where the sponge shows a mean density of 2.0 ind m−2. The present massive stranding event is the first in Sardinia and in the Mediterranean for this species, whose distribution is still poorly known. The living population of the gulf still seems in good status, and probably only a little percentage of specimens has been struck by the exceptionally strong hurricane. This work highlights the relevance of stranding events as opportunities for providing information about local biodiversity; biological traits of G. cydonium and the need of effective monitoring plans to fill the lack of knowledge about the distribution of this protected species are discussed.

The role of temporal resolution in modeling the wind induced sea surface transport in coastal seas

Abstract In this research work, the accuracy of a state of the art ocean model in reproducing the sea surface transport in coastal area using observed wind forcing data characterized by temporal resolution spanning between the day and the minute is analyzed. Numerical simulations were carried out to reproduce the paths of a set of surface drifters released in the Gulf of Oristano (Italy), a coastal area of the Mediterranean Sea. From the model results, a macroscopic increase of the quality of the ocean model predictions is observed when switching from day to hours in the temporal resolution of the atmospheric forcing. On the other hand, extending the analysis to lower sampling intervals, from 1 h to 1 min, this positive relationship is not found. The obtained results lead to consider that, when dealing with temporal resolution of the wind forcing spanning from hours to seconds, the use of the lowest sampling interval does not guarantee the highest accuracy in the ocean model predictions.

Geomorphology and environmental change around the Punic sites of the Terralba plain (Oristano Gulf, Sardinia, Italy)

We report a geomorphological study of the coastal plain of Terralba (SW coast of the island of Sardinia, Italy) in order to contextualize the high concentration of Punic rural settlements and analyze the environmental changes. The methodology is based on a detailed geomorphological study and sedimentological analysis of several records from different environments in artificial cuts and cores (chronology from archaeological remains and 14C dating). The study was also completed with information from various cartographic sources, and historical and geoarchaeological data. The Punic sites are located on a wide alluvial plain, modelled by aeolian sand mantles and wetlands, between the floodplain of the Sitzerri-Mannu and Mogoro rivers. Extensive aeolian units (Holocene and Pleistocene) are the most characteristic features of the geomorphology of the area. The results provide useful information on the environmental context of the Punic settlements on the coastal plain of Terralba, while evidence of significant geomorphological and environmental changes were found for over two millennia affecting the coastline, lagoon, marsh, aeolian and fluviodeltaic environments. The emergence of fresh water in the “paulis” or small depressions interspersed between dunes and well-drained soils suitable for cultivation have been a factor in the settlement of Punic farms.

Wind Fields From C- and X-Band SAR Images at VV Polarization in Coastal Area (Gulf of Oristano, Italy)

This work deals with the spatial characteristics of the wind fields evaluated from synthetic aperture radar (SAR) images and simulated by the weather research and forecasting (WRF) atmospheric model in the Gulf of Oristano, a small coastal area about $10\;\text{km} \times 18\;\text{km}$ wide in western coast of Sardinia (Western Mediterranean Sea). The SAR-derived wind fields have been obtained analyzing images of the COSMO-SkyMed, Radarsat-2, and Sentinel-1A satellites through a fully two-dimensional continuous wavelet transform (2-D-CWT) method. The analysis of the wind directions has shown that the model variability is limited if compared to that inferred by 2-D-CWT method, which mostly respects the variability evidenced by in situ data. As the use of model directions to compute the SAR wind fields is a standard in many studies, the impact on the SAR wind speed retrieval of using the model instead of the SAR-derived directions has been assessed: differences of wind speed greater than $\pm$ 10% occur for about the 20% of data. The spatial variability of the SAR and model wind speed fields results quite different at both local and domain scales. The knowledge of the spatial variations of the surface wind fields can be very important for the oceanographic applications and constitutes the added value brought by SAR in the description of the coastal wind. For this reason, the SAR-derived wind fields should be taken as reference in many kind of applications.

Combining place names and scientific knowledge on soil resources through an integrated ethnopedological approach

Local knowledge refers to the understandings, skills, and philosophies developed by societies with long histories of interaction with their environment. Place names (toponyms) can be considered an important mirror of the local knowledge and perceptions about the surrounding living space. The aim of this research has been to investigate, through an integrated ethnopedological approach, the meaning and distribution of toponyms, with particular (but not sole) reference to pedonyms (toponyms connected to soil resources) used in the traditional and recent cartography of Sardinia (southern Italy). As a paradigmatic case study, the toponyms belonging to an important sub-region of Sardinia, the Gulf of Oristano (central-western Sardinia), have been investigated.To draw appropriate comparisons between local and scientific knowledge, the research was conducted through the following approach: i) toponymy research and collection from different sources; ii) database creation and toponym translation; iii) categorization of toponyms; iv) soil field investigation and analysis of several physical–chemical parameters; and v) graphical, statistical (including multivariate analysis), and cartographic data processing.Generally speaking, the research shows that toponymy cannot be intended merely as a contextual geographic practice aiming to attribute a specific place name to a predefined geographical space. It rather represents a complex and articulated dynamic objectivation (in terms of the conversion of a concept or abstraction into an object) of a geographic entity. This process is the consequence of a strong, deep, and often conflicting interaction among humans, culture, and the surrounding environment. During the Anthropocene period, the influence of human activities on toponymy has been so intensive that many place names are now coined to mainly indicate the “artificial” man-made features of an intensively anthropized environment. Such “technogenic toponyms” could represent the “written witness” of the Anthropocene during subsequent eras.

The wind-measuring system in the Gulf of Oristano: a support for coastal-scale oceanographic applications

ABSTRACTThis paper describes a wind-measuring system (WMS) in the coastal area of the Gulf of Oristano, Sardinia, Italy. In this area, an oceanographic forecasting system based on a high-resolution finite-element hydrodynamic and wave model is operative. The system is forced by the wind fields provided by medium resolution (about 0.1×0.1 deg) atmospheric models. The high spatial resolution of the oceanographic prediction system (between 50 m and 1 km) is not accompanied by a similar resolution for atmospheric forcing. Therefore, the implementation of a WMS, aimed at accurately measuring the three-dimensional wind components, provides an essential tool to evaluate both the performance of the atmospheric models used to force the oceanographic models and the sensitivity of the oceanographic models to wind forcing of different qualities and spatial resolutions, the experimental fields included. This paper describes the WMS, the data collected and the geophysical quantities obtained from the time series of the three components of the wind sampled at high frequency. It also shows the results of comparisons between the experimental wind data and those from the atmospheric model at present used to force the oceanographic forecasting system. The information obtained from the WMS is unique, spanning from the spatial and temporal variability of the wind over the area of investigation to the evaluation of the basic quantities characterising the atmospheric boundary layer.

Stratigraphy, facies analysis and chronology of Quaternary deposits at Capo S. Marco (Sinis Peninsula, west Sardinia, Italy)

Capo S. Marco is the southernmost termination of the Sinis Peninsula in the northwestern border of the Oristano Gulf (western Sardinia, Italy). In the area, there are some of the most controversial and debated Quaternary deposits of Sardinia, consisting of beach, aeolian and slope sediments, whose chronological attribution changed according to different authors and, in different times, by the same authors. These discrepancies have not been solved by new radiometric dates, as radiocarbon and Optically Stimulated Luminescence (OSL) methods provided ages that are significantly different. During recent investigations at Capo S. Marco, beach notches filled with bioclastic sands, gravels, and boulders were discovered up to an elevation of ∼4.5 m, which is the highest elevation of the known beach notches. These sediments rest on aeolian deposits and form a marine terrace in two sites. In some places, these sediments also include small colonies of the coral Cladocora caespitosa in living position that have been recently dated by U/Th at 70 ± 4 ka and attributed to the end of MIS 5. Here, we report new U-series analyses of two samples of C. caespitosa collected on the uppermost part of the sequence. The U/Th ages of 153 ± 0.8 and 149 ± 0.6 ka would correspond to MIS 6, but the high values for the initial δ 234U (177 and 179) compared to the modern seawater value (147) point to an open-system addition of 234U and/or 230Th. The corrected ages using the open-system model of Thomson et al. are 141.6 ± 2 and 132 ± 2 ka. However, these deposits and the beach notches are not buried under aeolian or colluvial sediments, as are almost all the Tyrrhenian marine deposits found in Sardinia. They also rest on aeolian sediments, which, at San Giovanni di Sinis, were dated to MIS4 or Late MIS2 by OSL and radiocarbon dating of buried organic palaeosols, respectively. Accordingly, the stratigraphic evidence would suggest their attribution to the Holocene, although this contrasts with the Holocene sea level models available and the U/Th dating results.

Investigation into Cryptosporidium and Giardia in bivalve mollusks farmed in Sardinia region and destined for human consumption

Cryptosporidium and Giardia are protozoan parasites transmitted by fecal-oral ingestion of (oo)cysts, and are responsible for enteritis in several animal species and humans worldwide. These (oo)cysts can survive for over a year in aquatic environments and can accumulate in bivalve mollusks, which filter large volumes of water. The aim of this study is to evaluate the natural occurrence of Cryptosporidium and Giardia contamination in different specimens of edible bivalves mollusks from farming sites of the western and north-eastern coasts of Sardinia. From April 2011 to February 2012, 1095 specimens of Mytilus galloprovincialis and 240 of Crassostrea gigas were sampled from Olbia and Oristano gulf and San Teodoro pond. Hepatopancreas and gills, including the labial palp, were examined for oocysts and cysts after pooling and homogenisation using different techniques: i) staining for light and fluorescence microscopy; ii) direct immunofluorescence (IF) Merifluor® test Cryptosporidium/ Giardia (Meridian Bioscience Inc., Cincinnati, OH, USA); and iii) molecular procedures. However, in the context under study, all mollusks examined with the three main diagnostic techniques were negative for both parasites pointing out the hypothetically low zoonotic risk related to Cryptosporidium and Giardia in bivalves, especially Mytilus galloprovincialis and Crassostrea gigas.

Land Use History and Site Formation Processes at the Punic Site of Pauli Stincus in West Central Sardinia

The site of Pauli Stincus is located near the town of Terralba, on the inland shores of the Gulf of Oristano in west central Sardinia, Italy, and was occupied between the mid‐4th and the late 2nd century B.C. The site and its surroundings were the object of a joint archaeopedological and geomorphological study, which complemented the data from archaeological excavations. This study allowed us to evaluate the suitability of the different landscape and soil components for crop production in the Punic period. The discovery of a buried plow soil at the site's edge enabled us to identify a set of agricultural practices carried out by Punic farmers. These included the removal of sandy topsoil to cultivate deeper horizons enriched in illuvial clay, the use of a "sodbuster" or "rip ard," and the periodic burning of weeds, stubble, and other harvesting residues. The present study helped us to better understand the formation processes of the archaeological record at Pauli Stincus. Large quantities of allochtonous calcareous material were imported to the site from wet areas closer to the coast in order to produce earth‐based construction material, such as bricks and daub. © 2013 Wiley Periodicals, Inc.

The effect of hydrodynamics on shell orientation and population density of Pinna nobilis in the Gulf of Oristano (Sardinia, Italy)

Pinna nobilis is the largest endemic bivalve of the Mediterranean Sea, declared protected since 1992. Although hydrodynamic stress induced by waves is known to influence density, size and orientation of P. nobilis, the effect of other hydrological features is unknown. This paper considers a P. nobilis population living within a Posidonia oceanica meadow in the Gulf of Oristano (Sardinia, Italy). We hypothesize that spatial differences in density and orientation of P. nobilis may be related to significant wave height (HS), wave direction (DW), bottom current direction (DBC) and bottom current speed (SBC). A population of P. nobilis was investigated at different sites and its distribution was correlated to hydrodynamics by means of a numerical modeling approach. The spatial distribution was patchy, with a density of 0.06–6.7ind.100m−2. A non-uniform distribution of shell orientations (OS) was demonstrated in 4 sites out of 6. DBC and SBC were the main factors affecting OS, while waves had little influence. A SBC of 0.07ms−1 appears to be the threshold for inducing specimen directionality with shells aligned to the current and the ventral side exposed to the flow. This suggests that feeding strategy is a key factor in determining OS, in addition to drag minimization. We also highlighted the role of adjacent lagoons in supporting high densities as a result of high food availability. These findings demonstrate the usefulness of modeling techniques in explaining the spatial distribution pattern of P. nobilis and in contributing to our knowledge of its ecological traits.

A metabolic scope based model of fish response to environmental changes

Eco-physiology studies, performed in laboratory under controlled conditions, provide an essential tool for quantifying the impact of environmental changes on the metabolism and behaviour of individual fish. One way of quantifying such impact is by measuring the Metabolic Scope (MS) of a fish and how it is affected by environmental factors. Laboratory experiments were performed to calculate the empirical mathematical equations describing the variation of the MS of flathead grey mullet, Mugil cephalus, under different environmental conditions (water temperature and water oxygen concentration). The equation obtained was introduced into a coupled hydrodynamic–ecological numerical model able to reproduce the variability of the water temperature, salinity, dissolved oxygen, and of the main dissolved nutrients and chlorophyll-a. The coupled empirical–numerical model was used to reproduce the temporal and spatial variation in MS of a M. cephalus fish population in the Oristano gulf and the Cabras lagoon system (Italy), a typical Mediterranean shallow water environment. Results from numerical simulations show that during the spring and the beginning of summer period, Cabras lagoon provides a higher MS for M. cephalus than the Oristano gulf. During the rest of the year, apart from some transitional phases, the gulf provides more suitable conditions (higher MS) for M. cephalus. The obtained results are in general accordance with fisheries data, showing that M. cephalus catches are highest during the end-July to August period, as they migrate out of the lagoon. This approach, combined with observation on the temporal and spatial distribution of fishes, can allow predictions of fish productivity in non-limiting conditions.

Palynological interpretation of the Early Neolithic coastal open-air site at Sa Punta (central-western Sardinia, Italy)

The major goal of the present study has been to assess the ecological context of the Early Neolithic settlement under excavation in the coastal site of Sa Punta-Marceddì (Terralba, Sardinia, Italy) where a trench of Neolithic age has been brought to light. Based on the origins of the site's organic fossiliferous content, the purpose of this work is to achieve an understanding of: 1) the reasons why this location was chosen by EN man and 2) its functions. This research has enabled us to suggest a human paleoecological scenario over the course of the last three centuries of the 6th millennium BC in the inland area of the Oristano Gulf. On the basis of pollen spectra and the phytolith morphologies recognised, it is suggested that herbaceous vegetation covered the alluvial plain. Arable agriculture does not seem to have been practiced on the site, but the record of coprophilous fungi and endoparasites, along with clues that there were burning practices, suggest livestock farming activity. To date, a univocal interpretation of the function of this trench is still lacking. However, it is the oldest and the only evidence in Sardinia of a remarkable transformation of an open-air space due to settlement.

Density and distribution patterns of the endangered species Pinna nobilis within a Posidonia oceanica meadow in the Gulf of Oristano (Italy)

Pinna nobilis is an endemic bivalve of the Mediterranean Sea. In the last decades P. nobilis populations have declined drastically due to increasing anthropogenic pressure and it has been declared a protected species since 1992. Despite the need for conservation, knowledge of the ecology and monitoring of the main populations of P. nobilis are limited. This study considered a population living within a Posidonia oceanica meadow in the Gulf of Oristano (western Mediterranean, Italy). The study area, about 150 hectares, part of which is included within a Marine Protected Area and a Site of Community Importance, was subdivided in 3 sub-areas. The percentage cover of different habitat types (P. oceanica, dead matte and sand) in each sub-area was measured and meadow features (substrate coverage, matte compactness and shoot density) characterized. The hypotheses of differences in density, percentage of dead individuals, population structure, shell burial level and orientation of P. nobilis, were investigated according to sub-areas and to habitat type. The spatial distribution was patchy, and the habitat type resulted a key factor in determining both density and distribution. A strong edge effect was demonstrated: more than half of the observed individuals colonized the P. oceanica border. Matte compactness and shoot density were found to affect the density and distribution of P. nobilis. Shell burial level and percentage of dead individuals varied with sub-areas and habitat types. Size distribution was bimodal and common shell orientation was observed in two sub-areas. These results contribute to increase the knowledge of population ecology of this species and to provide useful information for implementing conservation policies.

Density, size structure, shell orientation and epibiontic colonization of the fan mussel <em>Pinna nobilis</em> L. 1758 (Mollusca: Bivalvia) in three contrasting habitats in an estuarine area of Sardinia (W Mediterranean)

We investigated the spatial distribution, size structure, shell orientation and valve colonization by epibionts of the endangered Mediterranean bivalve Pinna nobilis in three continuous but different habitats in the Gulf of Oristano (Sardinia, western Mediterranean). The sampling stations chosen were: an estuarine area (E) of coastal salt-marshes characterized by unvegetated sea-bottoms; and two areas in a seagrass meadow characterized by an extensive Posidonia oceanica meadow (Mw) and patched mixed meadows of P. oceanica and Cymodocea nodosa (Me). We found significant differences in mean densities among stations and the highest value was found in the estuarine area. Shell orientation showed that there was uniform circular distribution of specimens in the Mw station and a unimodal distribution in the Me and E stations, where specimens were set at 0°N and 10°NNE, which is a pattern related to sea drift. Shell epibiosis displayed differences between habitats. The highest valve colonization was in the estuary, with filamentous dark algae and Ostrea edulis reaching almost 90 percent of shell coverage. This study provides new information on habitat preferences and data for assessing local populations of P. nobilis that is useful for its conservation and improving the knowledge of its ecology.

Onshore to offshore reconstruction of the Messinian erosion surface in Western Sardinia, Italy: Implications for the Messinian salinity crisis

New outcrops in the Sinis peninsula (Sardinia, Italy) allow a detailed description of the Messinian erosion surface. The correlation between outcrops, industrial seismic data and data collected offshore Oristano from a recent cruise permits reconstruction of the geometry of this surface from presently emerged interfluves to the deep canyons offshore, with: - onshore: an eroded karstic plateau presently cropping out over a 20 km × 5 km area. Well-preserved karst structures occur locally and can form several metres high reliefs. The southernmost edge of the plateau is limited by a cliff. The karstic plateau and the cliff are sealed by transgressive deposits of Pliocene age; - offshore, an interfluve zone with a mostly flat and low-angle dipping plateau, westward dissected by paleovalleys which were identified down to a depth of 2000 m. In the Oristano Gulf, Messinian paleovalleys were also identified. The Capo San Marco paleocliff was probably located on the edge of a canyon. Onshore, only one major erosion surface was identified, located at the top the Messinian sequence. Offshore, this surface extends down to the abyssal plain. The surface was emplaced above deposits related to the Terminal Carbonate Complex. This indicates that the marginal evaporites are older than the major drawdown of the Mediterranean sea-level. The major drawdown is related to the deposition of the deep evaporites.

A Multidisciplinary and Ecosystemic Approach in the Oristano Lagoon-Gulf System (Sardinia, Italy) as a Tool in Management Plans

1 - This paper provides an overview of some of the research activities carried out in the Oristano Lagoon-Gulf system (western Sardinia, Italy) aimed at assessing the ecological quality of a complex transitional-coastal system renowned for its naturalistic and economical value, but subject to an increasing anthropogenic pressure. 2 - Numerical models concerning physical and ecological processes have been applied, including a fully coupled hydrodynamic-ecological model based on the finite element method, suited for application to lagoons and coastal seas. Different scenarios characterized by modified settings of the hydraulic balance between the Gulf of Oristano and the Cabras Lagoon have been considered and numerical simulations have been carried out to predict the evolution of both hydrological and ecological variables within the system under different meteorological forcing. 3 - Parallel investigations on the physical and chemical characteristics of the sediments and macrobenthic assemblages have been conducted in the Cabras Lagoon and the adjacent coastal area of the Gulf of Oristano. These studies have shown a close link between the distribution of organic-C bounding fine sediments (<8 µm grain size fractions) and benthic macroinvertebrates, and the water residence times computed from the model. In the Gulf, the structural and functional importance of Posidonia oceanica and Cymodocea nodosa seagrass meadows in sustaining a high biodiversity and as a natural trapping of fine particles is highlighted. 4 - Studies on the effect of hypoxia on ecophysiology, energetics and behaviour have been carried out on the various species of lagoon fishes (Liza aurata, Mugil cephalus and Dicentrarchus labrax), with the specific goal of identifying the thresholds for the effects of hypoxia, a common phenomenon occurring in coastal lagoons, on various physiological and behavioral traits (e.g. swimming energetics, escape performance). The results show that these thresholds ranged from 10 to 50% of air saturation, and were species- and variable-specific. 5 - Our multidisciplinary and ecosystemic approach, applicable to other similar systems, is aimed at supporting local administrations in decision making with regard to the management of the transitional and coastal waters of the Oristano Lagoon-Gulf system within the context of the European Water Framework Directive (WFD; EC, 2000).

Intrabasinal conditions promoting the development of a biogenic carbonate sedimentary facies associated with the seagrass Posidonia oceanica

This paper aims to elucidate the spatial relationships between the distribution and growth dynamics of Posidonia oceanica, the sedimentary depositional facies (carbonate vs. siliciclastic), and the hydrodynamic features of the Gulf of Oristano (Western Sardinia, Mediterranean sea), a complex depositional system characterized by multiple sources of sediments and a marked hydrodynamic gradient. Three depositional environments were identified: (i) a poorly vegetated sector characterized by muddy sediments derived from the river input; (ii) a sector colonized by P. oceanica meadows characterized by biogenic carbonate sediments derived from the sediment production associated with the seagrass ecosystem and (iii) a sector colonized by P. oceanica meadows characterized by coarse siliciclastic sediments, possibly relict sediments. The sedimentary depositional environments are heavily influenced by the spatial distribution of the wind wave energy. Biogenic carbonate reefs associated with P. oceanica meadows develop in sheltered areas characterized by low amplitude of waves generated by the main wind regime. In the exposed sectors, characterized by a higher wave height, the meadows colonize relict siliciclastic sediments, without promoting carbonate particle deposition. Posidonia oceanica meadows in sheltered areas, associated with biogenic sedimentary facies, exhibit higher rhizome growth rate values (1.1 and 1.2 cm year −1 vs. 0.7 cm year −1) and a lower percentage of horizontal shoots (1.1% and 4.1% vs. 18%) in comparison to P. oceanica meadows in exposed areas, associated with siliciclastic sedimentary facies. The former tend to develop in a vertical direction, thus contrasting the sediment deposition rate, the latter tend to expand laterally due to the absence of sediment deposition. These results highlight that wave amplitude is the intrabasinal factor which influences the deposition of biogenic sediments and the growth dynamics of P. oceanica meadows.