Restoration of the endemic hermatypic coral Cladocora caespitosa in the Mediterranean Sea: coral gardening based on micro-fragmentation

Abstract Cladocora caespitosa is the only reef-building zooxanthellate coral in the Mediterranean Sea. It forms beds of colonies, sporadically aggregating in extensive reef-like structures. The carbonate deposition of C. caespitosa enhances habitat complexity, supports biodiversity, and contributes to carbon sequestration. This species has been increasingly threatened by anthropogenic pressures. Due to its decline, the International Union for the Conservation of Nature (IUCN) included C. caespitosa in the endangered species list. Here we explored the available knowledge on tropical coral reefs to develop a protocol for the ecological restoration of this Mediterranean species. In this preliminary study, we exploited naturally occurring dislodged fragments as donor material and successfully implemented micro-fragmentation and nursery-rearing techniques on this species, designing a protocol for future restoration interventions. We reported that micro-fragmented C. caespitosa has optimal survival and growth rates surpassing those of naturally occurring juvenile colonies. We also showed that C. caespitosa fragments subjected to a strong heatwave, bleached but survived and recovered after the re-establishment of lower temperatures. Bleached individuals of C. caespitosa were able to grow, although to a much lower rates than those in healthy conditions. The coral gardening proposed here is highly successful, and can be operated at large spatial scales.