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Historical temperature variability affects coral response to heat stress.

Carilli J, Donner SD, Hartmann AC - PLoS ONE (2012)

Bottom Line: We investigated the influence of past temperature variability on coral susceptibility to bleaching, using the natural gradient in peak temperature variability in the Gilbert Islands, Republic of Kiribati.The spatial pattern in skeletal growth rates and partial mortality scars found in massive Porites sp. across the central and northern islands suggests that corals subject to larger year-to-year fluctuations in maximum ocean temperature were more resistant to a 2004 warm-water event.This study indicates that coral reefs in locations with more frequent warm events may be more resilient to future warming, and protection measures may be more effective in these regions.

View Article: PubMed Central - PubMed

Affiliation: Institute for Environmental Research, Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales, Australia. jcarilli@gmail.com

ABSTRACT
Coral bleaching is the breakdown of symbiosis between coral animal hosts and their dinoflagellate algae symbionts in response to environmental stress. On large spatial scales, heat stress is the most common factor causing bleaching, which is predicted to increase in frequency and severity as the climate warms. There is evidence that the temperature threshold at which bleaching occurs varies with local environmental conditions and background climate conditions. We investigated the influence of past temperature variability on coral susceptibility to bleaching, using the natural gradient in peak temperature variability in the Gilbert Islands, Republic of Kiribati. The spatial pattern in skeletal growth rates and partial mortality scars found in massive Porites sp. across the central and northern islands suggests that corals subject to larger year-to-year fluctuations in maximum ocean temperature were more resistant to a 2004 warm-water event. In addition, a subsequent 2009 warm event had a disproportionately larger impact on those corals from the island with lower historical heat stress, as indicated by lower concentrations of triacylglycerol, a lipid utilized for energy, as well as thinner tissue in those corals. This study indicates that coral reefs in locations with more frequent warm events may be more resilient to future warming, and protection measures may be more effective in these regions.

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Related in: MedlinePlus

Annual coral extension rates.Extension rates for individual coral cores standardized such that the long-term average for each record is equal to 1 cm/year.
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pone-0034418-g002: Annual coral extension rates.Extension rates for individual coral cores standardized such that the long-term average for each record is equal to 1 cm/year.

Mentions: We used the open-source program Osirix (version 3.8.1 with 64-bit extension) to reconstruct 3-d images of core density from CT scan data using the maximum intensity projection mode. We then selected the maximum growth axis and took a virtual 3.4-mm thick slice through the core along this axis, revealing the annual density banding in each core. We used the “length” tool in Osirix to select and extract density data in Hounsfield units on transects perpendicular to the clearest growth banding. Hounsfield units were converted to density using CT scans of aluminum wedges originally designed for calibrating x-ray density (see supplemental material in [11]). Annual bands were then identified manually between density minima, and the annual extension (cm/year), density (g/cm3/year), and calcification (extension * density; g/cm2/year) rates were calculated for the core. This was done twice along the length of each core in different locations, averaging the two series to construct the final growth record for each core, and finally standardizing to an average extension rate of 1 cm/year by dividing by the mean for each series (Figure 2). See Table S1 for average data before standardization from each site. Extension rates are presented here (Figure 2), as changes in calcification rates are mainly driven by extension due to minimal density fluctuations in these cores (Figure S1, S2); this has been found in other studies as well [11], [42]. Partial mortality scars were recognized by comparing anomalous features such as truncated density bands and very dense material in the CT scans with the original cores [43]. Tissue thickness was measured as the depth in the skeleton occupied by tissue, recognized visually, using calipers on the original cores [44].


Historical temperature variability affects coral response to heat stress.

Carilli J, Donner SD, Hartmann AC - PLoS ONE (2012)

Annual coral extension rates.Extension rates for individual coral cores standardized such that the long-term average for each record is equal to 1 cm/year.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3316685&req=5

pone-0034418-g002: Annual coral extension rates.Extension rates for individual coral cores standardized such that the long-term average for each record is equal to 1 cm/year.
Mentions: We used the open-source program Osirix (version 3.8.1 with 64-bit extension) to reconstruct 3-d images of core density from CT scan data using the maximum intensity projection mode. We then selected the maximum growth axis and took a virtual 3.4-mm thick slice through the core along this axis, revealing the annual density banding in each core. We used the “length” tool in Osirix to select and extract density data in Hounsfield units on transects perpendicular to the clearest growth banding. Hounsfield units were converted to density using CT scans of aluminum wedges originally designed for calibrating x-ray density (see supplemental material in [11]). Annual bands were then identified manually between density minima, and the annual extension (cm/year), density (g/cm3/year), and calcification (extension * density; g/cm2/year) rates were calculated for the core. This was done twice along the length of each core in different locations, averaging the two series to construct the final growth record for each core, and finally standardizing to an average extension rate of 1 cm/year by dividing by the mean for each series (Figure 2). See Table S1 for average data before standardization from each site. Extension rates are presented here (Figure 2), as changes in calcification rates are mainly driven by extension due to minimal density fluctuations in these cores (Figure S1, S2); this has been found in other studies as well [11], [42]. Partial mortality scars were recognized by comparing anomalous features such as truncated density bands and very dense material in the CT scans with the original cores [43]. Tissue thickness was measured as the depth in the skeleton occupied by tissue, recognized visually, using calipers on the original cores [44].

Bottom Line: We investigated the influence of past temperature variability on coral susceptibility to bleaching, using the natural gradient in peak temperature variability in the Gilbert Islands, Republic of Kiribati.The spatial pattern in skeletal growth rates and partial mortality scars found in massive Porites sp. across the central and northern islands suggests that corals subject to larger year-to-year fluctuations in maximum ocean temperature were more resistant to a 2004 warm-water event.This study indicates that coral reefs in locations with more frequent warm events may be more resilient to future warming, and protection measures may be more effective in these regions.

View Article: PubMed Central - PubMed

Affiliation: Institute for Environmental Research, Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales, Australia. jcarilli@gmail.com

ABSTRACT
Coral bleaching is the breakdown of symbiosis between coral animal hosts and their dinoflagellate algae symbionts in response to environmental stress. On large spatial scales, heat stress is the most common factor causing bleaching, which is predicted to increase in frequency and severity as the climate warms. There is evidence that the temperature threshold at which bleaching occurs varies with local environmental conditions and background climate conditions. We investigated the influence of past temperature variability on coral susceptibility to bleaching, using the natural gradient in peak temperature variability in the Gilbert Islands, Republic of Kiribati. The spatial pattern in skeletal growth rates and partial mortality scars found in massive Porites sp. across the central and northern islands suggests that corals subject to larger year-to-year fluctuations in maximum ocean temperature were more resistant to a 2004 warm-water event. In addition, a subsequent 2009 warm event had a disproportionately larger impact on those corals from the island with lower historical heat stress, as indicated by lower concentrations of triacylglycerol, a lipid utilized for energy, as well as thinner tissue in those corals. This study indicates that coral reefs in locations with more frequent warm events may be more resilient to future warming, and protection measures may be more effective in these regions.

Show MeSH
Related in: MedlinePlus