Habitat mapping, physical characteristics and benthic community of a rhodolith bed in the Pelagie Islands (Strait of Sicily, Mediterranean Sea) were studied through Multi–Beam Echo–Sounder (MBES), Remotely Operated Vehicle (ROV) and grab samples. The geomorphological analysis revealed an articulated and wide rhodolith bed; video inspections highlighted a bed with high coverage, few sandy patches and with a prevalence of the boxwork morphotype. A total of 207 taxa with 876 specimens were identified, and Polychaeta was the dominant taxon. Linguimaera caesaris, a Lessepsian benthic amphipod, was recorded in all sampling sites, and its presence represents an input to deepen the benthic assemblage research on the rhodolith bed. In terms of morphotype composition, dead/live ratio and species variability, the bed variability indicated a good status of health, although trawling signs were detected through ROV videos. The present study broadens the knowledge on Mediterranean rhodolith beds and supports the importance of survey and monitoring activities for the conservation and management of this important habitat.
All over the world marine waters are under increasing pressure from human activities affecting marine ecosystems. Several EU Directives require assessment of the condition of marine environments; in particular the Marine Strategy Framework Directive (MSFD) applies an ecosystem approach to the management of human activities. In this context, the mapping of pressures in a standardized and comparable way is a critical step to assess the spatial pattern, the temporal change and the ecological impacts of human pressures. Within the MSFD, one of the stressors directly affecting the seafloor is the Physical Loss (PL) pressure, representing the permanent or long-term alteration of marine habitats. The main purpose of this study was to propose a method to estimate the spatial extent of PL pressure in the framework of the Initial Assessment phase of the MSFD. Furthermore, considering that human activities PL-related cause the loss of benthic habitats, and that the Mediterranean sea is characterized by sensitive and protected habitats such as the biogenic substrates sensu MSFD, the distribution of PL pressure was overlaid with the distribution of the seabed habitats to estimate the loss of biogenic substrates. This study represents a useful tool for establishing the baseline condition for PL pressure, to compare future conditions and to evaluate different management scenarios. Moreover, it allows identification of the areas where pressure tends to accumulate as ‘hot spots’ on which to focus in future impact analyses and the areas where few stressors are present.
This paper aims to underline the importance of monitoring studies during the execution of activities, like beach nourishment using relict sands, that plan the use of innovative technology. In fact, environmental monitoring studies allow prompt intervention in the case of unexpected events or interference factors. Potential negative repercussions on the marine environment could not be estimated through characterization studies carried out ante operam. This paper reports the monitoring study carried out for beach nourishment along the South Latium coasts (Tyrrhenian sea). In this area Posidonia oceanica meadows are present. In this context, a detailed and updated cartography and the knowledge of the P. oceanica beds distribution (a "priority habitat" in the UE Habitats Directive) allowed prompt identification of potential effects on the seagrass caused by specific technical procedures of the beach nourishment, not well-known in the planning phase of the project.
The availability of wide area habitat maps is a key aspect for several marine assessment scenarios. The development of innovative, quick and low cost methods to produce such maps is therefore crucial to overcome the actual knowledge gap. Multibeam echosounder (MBES) backscatter data acquisition is largely used to collect geophysical data which are then post processed versus in situ data (sediment and/or biological samples) to classify the acoustic response (hereafter direct method). However, many parameters as roughness, porosity, presence of gas seeps, etc. strongly affect the results. In fact, a number of recent works highlight that the availability of backscatter and sediment data is not sufficient to evaluate the relationship between acoustic response and seabed substratum (De Falco et al., 2010; Ferrini and Flood, 2006; Goff et al., 2000; Sutherland et al., 2007). This is particularly true in big areas, which are often characterized by wide depth range and heterogeneous substrata and where in situ data can be insufficient. In order to exceed these critical aspects in backscatter data elaboration, a new procedure (indirect method) is presented in this work. The proposed classification method can be synthetized as follows: (1) MBES backscatter data cleaning and homogenization, (2) identification of "disturbed" areas (i.e. trawled areas, dredging areas, etc.), (3) MBES backscatter data clustering with identification of a high number of acoustic facies (a multiple of the sediment classes recorded by in situ samples), (4) association of different acoustic facies to a specific sampled sediment class. This procedure was tested in a study area located in the North Latium coast in the central Tyrrhenian Sea. This area extends 30 square kilometres with a depth range between 40 and 100 metres, mainly characterized by soft bottom. The application of the proposed method classifies six groups of acoustic facies allowing adequate control of the difference in backscatter response (i.e. due to attenuation with depth). Furthermore, this method provides encouraging results also in areas with a very low number of in situ samples. The comparison between direct and indirect methods confirms the usefulness of this approach for the identification of soft bottom habitats in wide areas.
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