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

Bongaerts P, Frade PR, Hay KB, Englebert N, Latijnhouwers KR, Bak RP, Vermeij MJ, Hoegh-Guldberg O - Sci Rep (2015)

Bottom Line: All three species associated with "deep-specialist" photosynthetic endosymbionts (Symbiodinium).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.

View Article: PubMed Central - PubMed

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.

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.

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Photos from the dominant coral species in the lower mesophotic: Agaricia grahamae, Agaricia undata and Madracis pharensis (with showing a close-up of the skeleton).
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f3: Photos from the dominant coral species in the lower mesophotic: Agaricia grahamae, Agaricia undata and Madracis pharensis (with showing a close-up of the skeleton).

Mentions: The substrate of the lower mesophotic zone (>60 m) at the study site on the leeward side of Curaçao (Fig. 1) was dominated by sediment, interrupted by patches of hard substrate harboring sparse communities of zooxanthellate corals. From the submersible footage, a total of 438 zooxanthellate coral colonies were observed at depths ≥60 m, with the deepest colonies recorded at a depth of 91 m (Madracis pharensis; n = 2). The coral community was dominated by Agaricia grahamae between 60–75 m and M. pharensis between 80–90 m (Fig. 2). M. pharensis could not be distinguished from Madracis senaria in the submersible footage, but collected specimens from ≥60 m depth were all identified as M. pharensis (n = 53) (Fig. 3). Similarly, A. grahamae could not be distinguished from Agaricia undata in the video transects. From the total number of collected Agaricia specimens ≥60 m depth at the study site (n = 65) several specimens at each depth (1 out of 17 at 60 m, 1 out of 19 at 75 m, 6 out of 25 at 80 m and 2 out of 4 at 90 m) were later identified in the lab as A. undata rather than A. grahamae (Fig. 3). In addition to A. grahamae, A. undata and M. pharensis, the only other zooxanthellate corals that were observed in the video transects were Montastraea cavernosa (n = 1), Agaricia lamarcki (n = 2) and Stephanocoenia intersepta (n = 1) at respectively 63, 74 and 81 m depth. Colony size frequency groups (Fig. 2) were not significantly different across depths for Agaricia (Global R = −0.044, P = 0.979) and Madracis (Global R = −0.003, P = 0.531). Colony morphologies of Agaricia consisted of unifacial plates (sometimes encrusting over dead Agaricia skeletons), whereas Madracis exhibited thinly encrusting colonies, usually following the shape of the underlying substrate. No signs of coral bleaching were observed, however human debris was frequently observed between 60–90 m, consisting of glass bottles, fishing line, ropes and small “disposable” anchors.


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

Bongaerts P, Frade PR, Hay KB, Englebert N, Latijnhouwers KR, Bak RP, Vermeij MJ, Hoegh-Guldberg O - Sci Rep (2015)

Photos from the dominant coral species in the lower mesophotic: Agaricia grahamae, Agaricia undata and Madracis pharensis (with showing a close-up of the skeleton).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4285725&req=5

f3: Photos from the dominant coral species in the lower mesophotic: Agaricia grahamae, Agaricia undata and Madracis pharensis (with showing a close-up of the skeleton).
Mentions: The substrate of the lower mesophotic zone (>60 m) at the study site on the leeward side of Curaçao (Fig. 1) was dominated by sediment, interrupted by patches of hard substrate harboring sparse communities of zooxanthellate corals. From the submersible footage, a total of 438 zooxanthellate coral colonies were observed at depths ≥60 m, with the deepest colonies recorded at a depth of 91 m (Madracis pharensis; n = 2). The coral community was dominated by Agaricia grahamae between 60–75 m and M. pharensis between 80–90 m (Fig. 2). M. pharensis could not be distinguished from Madracis senaria in the submersible footage, but collected specimens from ≥60 m depth were all identified as M. pharensis (n = 53) (Fig. 3). Similarly, A. grahamae could not be distinguished from Agaricia undata in the video transects. From the total number of collected Agaricia specimens ≥60 m depth at the study site (n = 65) several specimens at each depth (1 out of 17 at 60 m, 1 out of 19 at 75 m, 6 out of 25 at 80 m and 2 out of 4 at 90 m) were later identified in the lab as A. undata rather than A. grahamae (Fig. 3). In addition to A. grahamae, A. undata and M. pharensis, the only other zooxanthellate corals that were observed in the video transects were Montastraea cavernosa (n = 1), Agaricia lamarcki (n = 2) and Stephanocoenia intersepta (n = 1) at respectively 63, 74 and 81 m depth. Colony size frequency groups (Fig. 2) were not significantly different across depths for Agaricia (Global R = −0.044, P = 0.979) and Madracis (Global R = −0.003, P = 0.531). Colony morphologies of Agaricia consisted of unifacial plates (sometimes encrusting over dead Agaricia skeletons), whereas Madracis exhibited thinly encrusting colonies, usually following the shape of the underlying substrate. No signs of coral bleaching were observed, however human debris was frequently observed between 60–90 m, consisting of glass bottles, fishing line, ropes and small “disposable” anchors.

Bottom Line: All three species associated with "deep-specialist" photosynthetic endosymbionts (Symbiodinium).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.

View Article: PubMed Central - PubMed

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.

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.

Show MeSH