Seafloor Morphology and Inner Shelf Benthic Habitats of the Sinuessa Shallow Coralligenous Bank, Eastern Tyrrhenian Margin

Abstract

This study presents a high-resolution geomorphological and habitat map of the Sinuessa coastal sector (Tyrrhenian Sea), revealing the presence of an extensive and exceptionally shallow coralligenous bank developed between 5 and 16 m water depth. Multibeam bathymetry, side-scan sonar backscatter, sediment analyses, and Remotely Operated Vehicle (ROV) observations were integrated within a Geographic Information System (GIS) framework to characterize seabed morphology, acoustic facies, and associated benthic habitats. ROV surveys document a diverse macro- and epimegabenthic community, including both sciaphilous and photophilous taxa, as well as several protected and structuring species. Water depth alone does not discriminate among the mapped substrate classes (Kruskal–Wallis, p = 0.578), whereas acoustic backscatter, slope, and terrain ruggedness all do (p < 0.01), indicating that depth-independent controls govern the distribution of the bioconstruction. We hypothesize that persistently elevated turbidity and terrigenous input from the Volturno and Garigliano river systems reduce light penetration and generate, at 5–16 m, optical conditions comparable to those normally found at greater depths. This hypothesis is consistent with the geomorphological, sedimentological, and biological evidence presented here and with published oceanographic observations in the Gulf of Gaeta, but it has not been verified by in situ optical measurement, which we identify as the priority for future work. Relative backscatter intensity correlates significantly with mean grain size (Spearman ρ = −0.710, p < 0.001) and with gravel and mud content, and the four mapped classes differ significantly in backscatter, slope, and terrain ruggedness. These findings provide new insights into the environmental controls on coralligenous development and highlight the ecological relevance of shallow, turbidity-driven coralligenous systems within highly impacted Mediterranean coastal areas, with direct implications for habitat conservation and spatial management.