Tropical and temperate biogenic reefs are among the most important benthic ecosystems and their conservation is a major challenge for the maintenance and management of coastal marine systems. These reefs, because constituted by calcareous organisms, are sensitive to both anthropogenic pressures and climate changes, often acting simultaneously and therefore especially threatened at global scale.

This study investigated the structure and spatial variability of coralligenous assemblages of the Apulian continental shelf in the southern Adriatic Sea, consisting of small coralligenous outcrops distributed between 30 and 100 m of depth on coarse detritic or muddy bottom. Photographic samples, obtained through a Remotely Operated Vehicle (ROV), were analysed to evaluate the abundance of the main taxa or morphological groups of macroalgae and sessile invertebrates, and the deposited sediment. Results were compared between shallow (35-45 m) and deep outcrops (60-70 m).

The obtained results show that assemblages were dominated by encrusting and erect sponges, encrusting and filamentous algae, scleractinians, encrusting and erect bryozoans and the Zoantharia Parazoanthus axinellae. It was found that deep assemblages were characterized by lower diversity, and by the decrease or disappearance of encrusting sponges, P. axinellae and hydrozoans.

The authors suggest that higher sedimentation on deep outcrops may be the main driver of differences between shallow and deep assemblages. They highlight that in the study area, the deep outcrops may represent the result of a degradation process, as it is occurring in other parts of the Mediterranean continental shelf subjected to an increase of sedimentation. It is concluded that the information obtained from the Apulian continental shelf may represent a model to recognize shifts of coralligenous reefs in areas subjected to high sedimentation rates.

Piazzi et al. (2019) Deep coralligenous outcrops of the Apulian continental shelf: Biodiversity and spatial variability of sediment-regulated assemblages. Continental Shelf Research 172:50-56.