Grounds, Beds, and Reefs of the Endangered Coral Cladocora caespitosa with Description of the Tremiti Reef

Cladocora caespitosa (Cnidaria: Scleractinia: Cladocoridae) is an endangered coral species that forms peculiar ecosystems in the Mediterranean Sea. These are Cladocora grounds (aggregations of colonies, more or less spaced, on rocky bottoms), Cladocora beds (aggregations of unattached colonies, more or less spaced, on both soft and hard bottoms), and Cladocora reefs (formations with large colonies, mostly in contact with each other or with little space between them). This study provides an overview of the known presence and distribution of these three ecosystem types and describes newly discovered ones at Tremiti Islands Marine Protected Area (Adriatic Sea, Italy). Here, the Cladocora ground was present between 5 and 10 m depth, extending on 25,687 m2 (2.57 ha) with a mean density of 4.58 ± 0.45 colonies m−2, the Cladocora bed occurred between 15 and 23 m depth over 47,120 m2 (4.71 ha), with 8.59 ± 1.46 colonies m−2, while the Cladocora reef developed at 25–35 m depth, with a patchy distribution over 14,364 m2 (1.43 ha) and a mean density of 3.89 ± 0.17 colonies m−2. The spatial distribution, biometry, size structure, and conservation status of the Cladocora formations have been investigated and compared at the Mediterranean scale, where a total of 40 grounds, 3 beds, and 13 reefs have been currently documented. The role of environmental forcings in shaping the population structure of C. caespitosa and possibly driving the occurrence of each ecosystem type is discussed.