Corallith bed of the endangered coral Cladocora caespitosa in the South Adriatic Sea

The colonial coral Cladocora caespitosa is a Mediterranean-endemic scleractinian structuring ecosystems of great conservation and ecological importance. Their nomenclature is here revised distinguishing between three different C. caespitosa formations: beds, grounds and reefs. Here we describe an extensive C. caespitosa bed at Tremiti Islands (Italy, Adriatic Sea), where thousands of colonies develop as free-living coral nodules (coralliths) on a soft, detritic bottom. Colonies were seldom present shallower than 15 m depth as well as on rocky bottoms, while their density increased with depth up to 700 colonies 100 m− 2 at 22 m. Their bathymetric occurrence was primarily influenced by seawater temperatures, particularly during summer, when a marked thermocline act as protection against high temperatures. The conservation status of the C. caespitosa bed was overall good, with low epibiosis/necrosis, and negligible bleaching. Demographic traits and size-structure of both colonies and polyps (through corallites) are reported. These rare coral formations might be affected by anthropogenic threats at both local and global scale, thus appropriate conservation measures are needed to avoid significant impacts in the future.