title: Deep down on a Caribbean reef: lower mesophotic depths harbor a specialized coral-endosymbiont community.
abstract: 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.
authors.affiliation: 1] Global Change Institute, The University of Queensland, St Lucia, QLD 4072, Australia [2] ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, QLD 4072, Australia [3] CARMABI, Piscaderabaai z/n, PO Box 2090, Willemstad, Curaçao.
authors.forename: Pim
authors.initials: P
authors.lastname: Bongaerts
authors.affiliation: 1] CARMABI, Piscaderabaai z/n, PO Box 2090, Willemstad, Curaçao [2] Department of Limnology and Bio-Oceanography, Division of Marine Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Pedro R
authors.initials: PR
authors.lastname: Frade
authors.affiliation: Global Change Institute, The University of Queensland, St Lucia, QLD 4072, Australia.
authors.forename: Kyra B
authors.initials: KB
authors.lastname: Hay
authors.affiliation: 1] Global Change Institute, The University of Queensland, St Lucia, QLD 4072, Australia [2] ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, QLD 4072, Australia.
authors.forename: Norbert
authors.initials: N
authors.lastname: Englebert
authors.affiliation: 1] Global Change Institute, The University of Queensland, St Lucia, QLD 4072, Australia [2] University of Amsterdam, Science Park 904, 1090 GE, Amsterdam, The Netherlands.
authors.forename: Kelly R W
authors.initials: KR
authors.lastname: Latijnhouwers
authors.affiliation: 1] CARMABI, Piscaderabaai z/n, PO Box 2090, Willemstad, Curaçao [2] University of Amsterdam, Science Park 904, 1090 GE, Amsterdam, The Netherlands [3] Royal Netherlands Institute for Sea Research (NIOZ), Den Burg, The Netherlands.
authors.forename: Rolf P M
authors.initials: RP
authors.lastname: Bak
authors.affiliation: 1] CARMABI, Piscaderabaai z/n, PO Box 2090, Willemstad, Curaçao [2] University of Amsterdam, Science Park 904, 1090 GE, Amsterdam, The Netherlands.
authors.forename: Mark J A
authors.initials: MJ
authors.lastname: Vermeij
authors.affiliation: 1] Global Change Institute, The University of Queensland, St Lucia, QLD 4072, Australia [2] ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, QLD 4072, Australia.
authors.forename: Ove
authors.initials: O
authors.lastname: Hoegh-Guldberg
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D017691:Caribbean Region; D057894:Coral Reefs; D017753:Ecosystem; D014644:Genetic Variation; D005838:Genotype; D008928:Mitochondria / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D012335:RNA, Ribosomal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis / Q000235:genetics; D013696:Temperature
chemical_list: D012335:RNA, Ribosomal