Rehabilitating populations of Caribbean coral species that have declined in recent decades has become a management priority throughout the region, stimulating the development of new methodologies to arti cially reseed degraded reefs. Rearing lar- vae of ecologically important coral species appears a particularly attractive method to aid the recovery of degraded populations because genetic recombination could yield new genotypes better capable of coping with the altered conditions on modern Caribbean reefs. Well-developed elkhorn coral (Acropora palmata Lamarck, 1816) populations form dense thickets that contribute to the maintenance of healthy and productive reefs by providing shelter to a variety of other reef organisms (Gladfelter and Gladfelter 1978). After >95% of A. palmata populations were decimated by a disease beginning in the mid-1970s, this species was listed as critically endangered under the Red List of threatened Species (IUCN 2013) and restoration e orts were initiated throughout the region to assist its recovery (Young et al. 2012). In 2011, we collected gametes from eight A. palmata colonies in situ o Curaçao, which were subsequently cross-fertilized to generate larvae. Competent larvae were settled on clay tiles (Panel A) and reared in a ow-through land-based nursery for one year (Panels B–C), after which they were outplanted to a breakwater at 2–5 m depth (Panel D) [refer to Chamberland et al. (2015) for details on methodology]. Seven out of nine outplanted colonies survived and continued to grow in situ (Panels D–E), reaching a size of 30–40 cm diameter and 20–30 cm height after 4 yrs (Panel F). On 8 and 10 September, 2015, nine and 11 d after the full moon, two colonies were ob- served releasing gametes between 155 and 175 min after sunset (Panels G–H). is is the rst time that an endangered Caribbean Acropora coral species was raised from larvae and grown to sexual maturity in the eld. Indeed, only one other study has documented age and colony size at reproductive onset in a broadcast spawning scler- actinian coral reared from larvae (Baria et al. 2012). e relatively short time until onset of spawning (≤4 yrs) observed for A. palmata shows that recovery of degraded coral populations by enhancing natural recruitment rates may be practicable if out- planted colonies are able to rapidly contribute to the natural pool of larvae.
The composition, ecology and environmental conditions of mesophotic coral ecosystems near the lower limits of their bathymetric distributions remain poorly understood. Here we provide the first in-depth assessment of a lower mesophotic coral community (60–100 m) in the Southern Caribbean through visual submersible surveys, genotyping of coral host-endosymbiont assemblages, temperature monitoring and a growth experiment. The lower mesophotic zone harbored a specialized coral community consisting of predominantly Agaricia grahamae, Agaricia undata and a “deep-water” lineage of Madracis pharensis, with large colonies of these species observed close to their lower distribution limit of ~90 m depth. All three species associated with “deep-specialist” photosynthetic endosymbionts (Symbiodinium). Fragments of A. grahamae exhibited growth rates at 60 m similar to those observed for shallow Agaricia colonies (~2–3 cm yr −1), but showed bleaching and (partial) mortality when transplanted to 100 m. We propose that the strong reduction of temperature over depth (Δ5°C from 40 to 100 m depth) may play an important contributing role in determining lower depth limits of mesophotic coral communities in this region. Rather than a marginal extension of the reef slope, the lower mesophotic represents a specialized community, and as such warrants specific consideration from science and management.