| A coral bed of the scleractinian Cladocora caespitosa is documented for the first time in the Gulf of Kalloni, Lesvos Island, Greece. It is among the largest Cladocora reefs in the Mediterranean, which covers an area of approximately 1,100 m2 over a muddy substrate, up to 5.8 m depth. Overall, 1,492 colonies were visually sampled in situ by scuba divers in order to assess their size, coral surface area, necrosis level, type of necrosis and whether they were attached to the substrate (fixed) or not (mobile). Distribution maps of coral abundance, coral covera and necrosis data were generated. A mean coral density of 4.79±2.25 colonies/m2 was obtained. The most typical size range in the study area was 10-20 cm, with an average major axis (D1) of 22.52±18.81 cm. Interestingly, aggregated colonies were frequently found, reaching up to 203 cm in diameter. Almost 80% of the colonies sampled were stuck to the substrate. An elevated number of coral fragments and rubble was also found on the sediment, but further research is needed to define their drivers, e.g. on the hydrodynamics of the area. A mean necrosis percentage of 34.6±38.2% was recorded, whilst most corals showed had no necrotic tissue. This good average state places the Cladocora population of Kalloni among the healthiest ones in the Mediterranean Sea. Necrosis was associated with epibionts in most cases. However, high spatial differences were detected for these parameters throughout the study area, generally showing a higher abundance of colonies around the central region, i.e. the main reef. Correlation analyses were performed between some environmental variables and coral characteristics. A qualitative analysis of the reef’s biodiversity was also conducted, taking underwater photographs for the posterior species identification. In total, 10 macrophyte and 64 animal taxa were identified in the coral reef of Kalloni. Besides, biotic assemblages between dead and alive coral colonies and other marine animals such as sponges or anemones were reported. Since C. caespitosa has been included in the IUCN Red List as an Endangered species, its conservation should be a priority. Therefore, a restoration project based on direct transplantation is proposed to be carried out in the Gulf of Kalloni to recover damaged colonies and enhance their viability, ultimately increasing their abundance. In addition, genetic analyses are proposed for future studies. As the Cladocora population of Kalloni regularly faces temperatures that are close to the species’ thermal limits on a regular basis, corals may thus have developed some adaptations, which would be of great interest to establish key features that might turn corals more resistant to the effects of climate change. |