The White Coral Community in the Central Mediterranean Sea Revealed by ROV Surveys

TLDR

White coral communities form complex bathyal reef structures that attract organisms and influence hydrodynamics, yet only a few extant reefs are known in the Mediterranean, contrasting with their abundant distribution in the Atlantic. This paper reports on a HERMES cruise dedicated to exploring rough submarine topographies in the central Mediterranean to search for white coral communities and re‑evaluate the perceived paucity of such reefs. The HERMES project employed state‑of‑the‑art mapping and visualization technology to extend study sites deep into the Mediterranean. ROV inspections of narrow shelves, canyon walls, escarpments, and seamounts uncovered many previously unknown coral sites.

Abstract

White coral communities consist of scleractinian corals that thrive in the ocean’s bathyal depths (~ 200–4000 m). In the Atlantic Ocean, white corals are known to form complex, three-dimensional structures on the seabed that attract vast amounts of other organisms, accumulate suspended detritus, and influence the local hydrodynamic flow field. These attributes coincide with what we generally describe as a coral reef. With time, environmental change causes decline of the framework-constructing corals; this is followed by erosion of the reef sequence or its draping with noncoral-related deposits. After several such sequences, the structures are known as coral carbonate mounds, which can grow as high as 350 m. Both bathyal white coral reefs and mounds are widely distributed in the Atlantic Ocean and adjacent marginal seas, such as the Gulf of Mexico. The Mediterranean Sea, however, known for its richness of fossil white coral communities exposed in land outcrops, harbors very few extant coral communities. The HERMES project extended its study sites deep into the Mediterranean with state-of-the-art mapping and visualization technology. By doing so, many previously unknown coral sites were discovered during inspections of Mediterranean narrow shelves, canyon walls, escarpments, and seamounts by remotely operated vehicles. Such shelf and continental margin settings are characteristic of the dynamic margins of the Mediterranean Sea and contrast significantly with the much broader shelves of the Atlantic Ocean. This paper reports on a HERMES cruise that was dedicated to exploring these rough submarine topographies in search of white coral communities in the central Mediterranean, and re-evaluates the general perception of the assumed paucity of white corals in this sea.