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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Transplantation experiment visual summary: health status of individual fragments at the beginning of the experiment (March 2013), in the middle (August 2013) and at the end (February 2014).Fragments are grouped in pairs representing “clones” taken from the same A. grahamae colony, with the pair noted in blue coming from the same A. undata colony. Fragments from the same colony are depicted at the same position on each of the “racks” for comparative purposes, although in reality fragments were assigned to random positions. On the right, two examples of fragments from 60 m depth (indicated in the schematic by #1 and #2) are shown to demonstrate the increase in fragment diameter over the duration of the experiment.
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f8: Transplantation experiment visual summary: health status of individual fragments at the beginning of the experiment (March 2013), in the middle (August 2013) and at the end (February 2014).Fragments are grouped in pairs representing “clones” taken from the same A. grahamae colony, with the pair noted in blue coming from the same A. undata colony. Fragments from the same colony are depicted at the same position on each of the “racks” for comparative purposes, although in reality fragments were assigned to random positions. On the right, two examples of fragments from 60 m depth (indicated in the schematic by #1 and #2) are shown to demonstrate the increase in fragment diameter over the duration of the experiment.

Mentions: Coral fragments originating from eight A. grahamae colonies and one A. undata colony at ~80 m depth were transplanted to racks at 60, 80 and 100 m (n = 18 per rack). The fragments were visually assessed using the submersible 6–7 days after initial deployment and no signs of bleaching or partial mortality were observed. After 5 months, all fragments except for one on the 80 m rack showed signs of bleaching and/or mortality. At the end of the experiment (after ~10 months), all but three fragments on the 80 m rack had died (Fig. 8) and the surviving corals showed negligible growth (linear increase ranging from 1.8–2.4 mm) (Supplement Table 3, 4). On the 100 m rack, all but one of the fragments were found to be fully pigmented with no signs of bleaching or mortality after 5 months, however after 10 months most corals were still alive but almost all showed signs of bleaching and/or partial mortality. Again, growth was negligible (linear increase ranging from 0.0–3.7 mm) (Supplement Table 3, 4). On the 60 m rack, most fragments (13 out of 15) were still alive after 10 months (the 60 m rack was not checked after 5 months) and all but two had grown, with the six coral fragments that were still fully pigmented exhibiting an average linear increase in diameter of 19.4 mm (ranging from 5.7 to 27.2 mm) (Supplement Table 3, 4).


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)

Transplantation experiment visual summary: health status of individual fragments at the beginning of the experiment (March 2013), in the middle (August 2013) and at the end (February 2014).Fragments are grouped in pairs representing “clones” taken from the same A. grahamae colony, with the pair noted in blue coming from the same A. undata colony. Fragments from the same colony are depicted at the same position on each of the “racks” for comparative purposes, although in reality fragments were assigned to random positions. On the right, two examples of fragments from 60 m depth (indicated in the schematic by #1 and #2) are shown to demonstrate the increase in fragment diameter over the duration of the experiment.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f8: Transplantation experiment visual summary: health status of individual fragments at the beginning of the experiment (March 2013), in the middle (August 2013) and at the end (February 2014).Fragments are grouped in pairs representing “clones” taken from the same A. grahamae colony, with the pair noted in blue coming from the same A. undata colony. Fragments from the same colony are depicted at the same position on each of the “racks” for comparative purposes, although in reality fragments were assigned to random positions. On the right, two examples of fragments from 60 m depth (indicated in the schematic by #1 and #2) are shown to demonstrate the increase in fragment diameter over the duration of the experiment.
Mentions: Coral fragments originating from eight A. grahamae colonies and one A. undata colony at ~80 m depth were transplanted to racks at 60, 80 and 100 m (n = 18 per rack). The fragments were visually assessed using the submersible 6–7 days after initial deployment and no signs of bleaching or partial mortality were observed. After 5 months, all fragments except for one on the 80 m rack showed signs of bleaching and/or mortality. At the end of the experiment (after ~10 months), all but three fragments on the 80 m rack had died (Fig. 8) and the surviving corals showed negligible growth (linear increase ranging from 1.8–2.4 mm) (Supplement Table 3, 4). On the 100 m rack, all but one of the fragments were found to be fully pigmented with no signs of bleaching or mortality after 5 months, however after 10 months most corals were still alive but almost all showed signs of bleaching and/or partial mortality. Again, growth was negligible (linear increase ranging from 0.0–3.7 mm) (Supplement Table 3, 4). On the 60 m rack, most fragments (13 out of 15) were still alive after 10 months (the 60 m rack was not checked after 5 months) and all but two had grown, with the six coral fragments that were still fully pigmented exhibiting an average linear increase in diameter of 19.4 mm (ranging from 5.7 to 27.2 mm) (Supplement Table 3, 4).

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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