Growth and survival dynamics of mesophotic coral juveniles in shallow reefs

As many degrading shallow reefs suffer from recruitment failure, mesophotic coral ecosystems have been suggested as a potential source of coral propagules promoting the recolonization of these reefs. However, whether mesophotic coral populations can repopulate shallower reefs is currently debatable. Here, we compared the response of corals settled on mesophotic (50 m) tiles and transplanted to the shallow reef (10 m), at a Nature Reserve and an unprotected site in the northern Gulf of Eilat/Aqaba, Red Sea. Mortality was substantially higher for the transplanted corals, as compared with their shallow counterparts living on the tiles, with over half of the transplanted juveniles dying 1 yr post-transplantation. Transplanted corals exhibited a 24% higher survivorship at the MPA site. We further explored the survival and growth rates of the 4 most common transplanted coral genera (Cyphastrea, Porites, Psammocora, and Stylophora). An inverse relationship between survival and growth was evident among the transplanted coral genera; Porites and Stylophora demonstrated similar net growth rates to those of their shallow-water counterparts but lower post-transplantation survivorship, while Cyphastrea and Psammocora showed the opposite trend. Although this study demonstrates the reduced plasticity of mesophotic coral juveniles to cope with shallow-water conditions, it nonetheless offers some potential to facilitate shallow-reef recovery.