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Dissepiments, density bands and signatures of thermal stress in Porites skeletons
- Source :
- Coral Reefs. 36:749-761
- Publication Year :
- 2017
- Publisher :
- Springer Science and Business Media LLC, 2017.
-
Abstract
- The skeletons of many reef-building corals are accreted with rhythmic structural patterns that serve as valuable sclerochronometers. Annual high- and low-density band couplets, visible in X-radiographs or computed tomography scans, are used to construct age models for paleoclimate reconstructions and to track variability in coral growth over time. In some corals, discrete, anomalously high-density bands, called “stress bands,” preserve information about coral bleaching. However, the mechanisms underlying the formation of coral skeletal density banding remain unclear. Dissepiments—thin, horizontal sheets of calcium carbonate accreted by the coral to support the living polyp—play a key role in the upward growth of the colony. Here, we first conducted a vital staining experiment to test whether dissepiments were accreted with lunar periodicity in Porites coral skeleton, as previously hypothesized. Over 6, 15, and 21 months, dissepiments consistently formed in a 1:1 ratio to the number of full moons elapsed over each study period. We measured dissepiment spacing to reconstruct multiple years of monthly skeletal extension rates in two Porites colonies from Palmyra Atoll and in another from Palau that bleached in 1998 under anomalously high sea temperatures. Spacing between successive dissepiments exhibited strong seasonality in corals containing annual density bands, with narrow (wide) spacing associated with high (low) density, respectively. A high-density “stress band” accreted during the 1998 bleaching event was associated with anomalously low dissepiment spacing and missed dissepiments, implying that thermal stress disrupts skeletal extension. Further, uranium/calcium ratios increased within stress bands, indicating a reduction in the carbonate ion concentration of the coral’s calcifying fluid under stress. Our study verifies the lunar periodicity of dissepiments, provides a mechanistic basis for the formation of annual density bands in Porites, and reveals the underlying cause of high-density stress bands.
- Subjects :
- 0301 basic medicine
010504 meteorology & atmospheric sciences
biology
Coral bleaching
Coral
Porites
Aquatic Science
biology.organism_classification
01 natural sciences
Stress (mechanics)
03 medical and health sciences
Paleontology
chemistry.chemical_compound
030104 developmental biology
Calcium carbonate
chemistry
Sclerochronology
Paleoclimatology
14. Life underwater
Coral growth
Geology
0105 earth and related environmental sciences
Subjects
Details
- ISSN :
- 14320975 and 07224028
- Volume :
- 36
- Database :
- OpenAIRE
- Journal :
- Coral Reefs
- Accession number :
- edsair.doi...........6652a55a68bac344c5bd40fd80b037a0