Long-term viability, growth and reproduction of transplanted Astroides calycularis (Pallas, 1766) coral colonies in a polluted coastal area: Evidence from a four-year restoration study

The Mediterranean orange coral Astroides calycularis is a habitat-forming scleractinian species affected by multiple anthropogenic pressures, including coastal development, pollution, and destructive fishing activities, but also suitable for restoration actions. In this study, we evaluated the long-term viability of transplanted A. calycularis colonies in the polluted Site of National Interest (SNI) of Bagnoli-Coroglio (Italy, Tyrrhenian Sea), a former industrial area where the species historically occurred. In 2020, eighty-eight coral colonies (corals of opportunity) were collected from a donor site and subsequently transplanted and, four years later, monitored to assess survival, polyp proliferation, and colony growth. After four years, 31.8 % of the colonies survived, both polyp number and colony area had significantly increased, by approximately two-fold and three-fold, respectively, indicating tolerance and growth potential. Moreover, the record of a subset of small-sized colonies, likely representing juvenile recruits, suggested successful in situ sexual reproduction, larval settlement and growth. This study provides evidence that A. calycularis transplants can potentially persist, grow, and reproduce in areas that have not yet been restored, where the anthropogenic impact that caused its local extinction has not been completely removed. Our results support the feasibility of using A. calycularis in active restoration actions even in suboptimal areas from an ecological point of view.