Geomorphological characterization, spatial distribution and environmental status assessment of coralligenous reefs along the Latium continental shelf

Coralligenous reefs are typical underwater seascapes of the Mediterranean Sea and are ranked among the most relevant ecosystems of the basin and a pole of biodiversity. For their critical importance for ecosystems conservation, coralligenous reefs are included among the indicators that should be assessed under the Marine Strategy Framework Directive (MSFD). However, information regarding their spatial distribution and the influence of environmental factors on their structure and biological characteristics is still poor. As part of monitoring regional programs for the implementation of the MSFD in Italy, an extensive study was performed along the Latium continental shelf, aimed to define and map the distribution of coralligenous reefs and to assess their environmental status in three different study areas, characterized by different environmental conditions and subjected to different potential levels of human pressure. For each area, a large dataset was collected, including multibeam bathymetry, side scan sonar records and ROV video transects. The integrated analysis of geophysical data and ROV videos allowed to identify the morpho-acoustic facies indicative of coralligenous outcrops and to map their distribution across the study areas. In parallel, a quantitative analysis of video transects was carried out, in order to characterize the megabenthic communities in terms of species composition, abundance, health status of structural species, and to evaluate the abundance of marine litter. The environmental status of the coralligenous communities was then assessed through the application of the Mesophotic Assemblages Conservation Status (MACS) index. The results obtained showed a large variability in the distribution and characteristics of coralligenous reefs and associated assemblages along the Latium continental shelf, likely reflecting the different environmental conditions and human pressure in the different areas. Coralligenous reefs were reported from all the investigated areas, hosting a rich and varied associated fauna with dense gorgonian forests, also featuring species of relevance for conservation such as Corallium rubrum. The application of MACS index allowed to distinguish among a wide range of ecological conditions of the coralligenous communities, spanning from high to poor environmental status across different sites. The assessment of the extent and diversity of coralligenous assemblages through the combination of geomorphological analysis, acoustic mapping and quantitative video analysis represents an efficient tool, which may help governments and stakeholders making informed management decisions for future coastal planning and conservation strategies.