Deep down on a Caribbean reef: lower mesophotic depths harbor a specialized coral-endosymbiont community

• DOI: 10.1038/srep07652
• Publication Date: 2015-01-07T10:18:55Z
• Authors: Pim Bongaerts; Pedro R. Frade; Kyra B. Hay; Norbert Englebert; Kelly R. W. Latij...; Rolf P. M. Bak; Mark J. A. Vermeij; Ove Hoegh-Guldberg
• Keywords: 0106 biological sciences; 570; Genotype; Molecular Sequence Data; 551; 01 natural sciences; Article; Discovery Bay; Animals; 14. Life underwater; Symbiosis; Ecosystem; Phylogeny; Scleractinian Corals; Coral Reefs; Temperature; Genetic Variation; Agaricia agaricites; Red Sea; Anthozoa; Mitochondria; Caribbean Region; RNA, Ribosomal; 1000 General; Florida Shelf

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.