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Abstract The ecological distribution of coral species from shallow to mesophotic reefs is dependent on light, which varies drastically among local environments. Current definitions of mesophotic coral ecosystems primarily rely on a 30‐m recreational SCUBA boundary to define the upper limits of the community; however, this boundary does not consider local conditions and physiological adaptions of coral species. Using in situ benthic imagery and chlorophyll fluorescence measurements, we examined species distribution and community similarity, as well as photoacclimatization of two common depth‐generalist species (Montastraea cavernosaandPorites astreoides) across shallow to mesophotic reef zones at Little Cayman Island. Photoquadrat image analysis revealed a significant shift in coral species assemblages between 25 and 35 m, which was accompanied by a 30% drop in available surface light, suggesting light is a key driver of coral community composition. Patterns of photoacclimatization across depths differed significantly between the two coral species, with available surface light and the quantum yield of photochemistry in photosystem II found to be significant determinants of each species' abundance. These results provide valuable baseline data on coral community composition across a broad depth gradient in Little Cayman that can contribute to a growing body of evidence to set an upper boundary of mesophotic reefs based on light availability and photoacclimatization potential of depth‐generalist species.
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Phenotypic variability of Montastraea cavernosa and Porites astreoides along a depth gradient from shallow to mesophotic reefs in the Cayman Islands
Abstract Phenotypic variability is the ability of the same species to express different phenotypes under different environmental conditions. Several coral species that exist along a broad depth distribution have been shown to differ in skeletal morphology and nutrient acquisition at different depths, which has been attributed to variability in response to differing levels of light availability. This study examined the phenotypic variability of two common depth generalist corals,Montastraea cavernosaandPorites astreoides,along a gradient from 10 to 50 m in the Cayman Islands, by examining changes in skeletal morphology, photophysiology, symbiont cell density, and chlorophyll concentration. Skeletal features ofM. cavernosawere found to increase in size from 10 to 30 m, but returned to smaller sizes from 30 to 50 m, whileP. astreoidesskeletal features continued to increase in size from 10 to 40 m. No differences were observed in either symbiont density or chlorophyll concentration across depths for either species. However, all photophysiological parameters exhibited significant depth-dependent variations in both species, revealing adaptive strategies to different light environments. These results suggest that both species have high variability in response to depth. Patterns of skeletal morphology and photophysiology, however, suggest thatM. cavernosamay be more variable in regulating photosynthetic efficiency compared toP. astreoides, which likely facilitates the broader depth distribution of this species.
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- Award ID(s):
- 1937770
- PAR ID:
- 10533801
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Coral Reefs
- Volume:
- 43
- Issue:
- 5
- ISSN:
- 0722-4028
- Format(s):
- Medium: X Size: p. 1173-1187
- Size(s):
- p. 1173-1187
- Sponsoring Org:
- National Science Foundation
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