Time-integrated thermal bleaching thresholds of reefs and their variation on the Great Barrier Reef

Berkelmans, Ray

doi:10.3354/meps229073

Cited by 208 publications

(179 citation statements)

References 21 publications

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“…The unusually warm sea temperatures on the GBR in the summer 2002 was the principal trigger for the worst mass bleaching event on record with approximately 54% of reefs experiencing some bleaching over the 2000 km length of the GBR (Berkelmans, 2002;Berkelmans et al, 2004). The tagged colonies of A. millepora at Nelly Bay, first displayed visual signs of bleaching in early January 2002, and by 24 January 2002, all colonies displayed some level of bleaching.…”

Section: Discussionmentioning

confidence: 99%

Changes in coral-associated microbial communities during a bleaching event

et al. 2007

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Environmental stressors such as increased sea surface temperatures are well-known for contributing to coral bleaching; however, the effect of increased temperatures and subsequent bleaching on coral-associated microbial communities is poorly understood. Colonies of the hard coral Acropora millepora were tagged on a reef flat off Magnetic Island (Great Barrier Reef) and surveyed over 2.5 years, which included a severe bleaching event in January/February 2002. Daily average water temperatures exceeded the previous 10-year average by more than 1 1C for extended periods with field-based visual surveys recording all tagged colonies displaying signs of bleaching. During the bleaching period, direct counts of coral zooxanthellae densities decreased by B64%, before recovery to pre-bleaching levels after the thermal stress event. A subset of three tagged coral colonies were sampled through the bleaching event and changes in the microbial community elucidated. Denaturing gradient gel electrophoresis (DGGE) analysis demonstrated conserved bacterial banding profiles between the three coral colonies, confirming previous studies highlighting specific microbial associations. As coral colonies bleached, the microbial community shifted and redundancy analysis (RDA) of DGGE banding patterns revealed a correlation of increasing temperature with the appearance of Vibrio-affiliated sequences. Interestingly, this shift to a Vibrio-dominated community commenced prior to visual signs of bleaching. Clone libraries hybridized with Vibrio-specific oligonucleotide probes confirmed an increase in the fraction of Vibrio-affiliated clones during the bleaching period. Post bleaching, the coral microbial associations again shifted, returning to a profile similar to the fingerprints prior to bleaching. This provided further evidence for corals selecting and shaping their microbial partners. For non-bleached samples, a close association with Spongiobacter-related sequences were revealed by both clone libraries and DGGE profiling. Despite Vibrio species being previously implicated in bleaching of specific coral species, it is unsure if the relative increase in retrieved Vibrio sequences is due to bacterial infection or an opportunistic response to compromised health and changing environmental parameters of the coral host. This study provides the first molecular-based study demonstrating changes in coral-associated bacterial assemblages during a bleaching event on a natural reef system.

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Section: Discussionmentioning

confidence: 99%

Changes in coral-associated microbial communities during a bleaching event

et al. 2007

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“…Although the temperatures reported here represent those at the sea surface rather than at the depth of sampling, satellite-derived SSTs are common proxies for temperatures experienced by corals at relatively shallow depths, and have been used to accurately predict bleaching events (e.g. Jokiel & Coles 1990, Goreau & Hayes 1994, Strong et al 1997, Berkelmans 2002, McClanahan et al 2007). …”

Section: Methodsmentioning

confidence: 99%

Novel algal symbiont (Symbiodinium spp.) diversity in reef corals of Western Australia

Silverstein

Correa

LaJeunesse³

et al. 2011

Mar. Ecol. Prog. Ser.

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The identity and diversity of algal symbionts (Symbiodinium spp.) in reef corals is thought to influence to the resilience of reef ecosystems to climate change, and varies depending on coral species, environmental conditions, and biogeography. We examined these factors by surveying corals along a latitudinal gradient in Western Australia on reefs connected north to south by the warm-water Leeuwin Current. We used the internal transcribed spacer-2 (ITS-2) region of ribosomal DNA to characterize Symbiodinium communities in 19 species of reef coral (in 16 genera) from tropical Dampier (20.5°S) to temperate Dunsborough (33.5°S). We documented a high number of novel ITS-2 types in Symbiodinium clades B (1 type) and C (14 types) as well as 7 previously reported ITS-2 types in clades B, C, and D. In addition, we compared symbiont distributions with Giovanni's OBIG MODIS-Aqua satellite temperature data set and found that the putatively thermotolerant Symbiodinium ITS-2 type D1a was more frequently detected in 'chronically warm' tropical sites than at 'chronically cool' temperate sites, while clade B symbiont types showed the reverse pattern, being found in certain corals at the southernmost sites. Symbiodinium type D1a was generally most abundant at Dampier, where bleaching had occurred 1 mo prior to sampling, although some variation by host taxa was observed. The diverse and novel Symbiodinium communities documented here may be a result of (1) the variable environmental histories of the study sites, (2) the apparent genetic divergence within this genus resulting from the relative isolation of Western Australian reefs, and/or (3) the frequent transport of symbionts (in hospite or free-living) from Indo-Malay reefs to Western Australia via the Leeuwin Current. These results indicate that understudied reefs in remote and isolated areas may contain Symbiodinium diversity that has not been reported previously.

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“…The control pH (zero CO2 dosing, corresponding to an atmospheric CO2 of 380 ppmV) ranged from 8.0 to 8.4, resulting in an estimated pCO2 range of 130 -465 ppm reflecting the diurnal variability of the intake water from the reef. To determine interactions with temperature in a factorial design, CO2 treatments were crossed with two temperature regimes representing low and high average summer temperatures for the region (25-26°C and 28 -29°C) (15). On the basis of measurements of pH, temperature, and total alkalinity [measured using the Gran alkalinity method (40) on a Mettler Toledo T50 automated titrator using 0.1M HCL for 130 g seawater samples], and salinity (measured using a Bellingham Stanley refractometer), the distribution of carbon species and aragonite saturation state were estimated for all treatments (Table 1) using the program CO2SYS (41).…”

Section: Methodsmentioning

confidence: 99%

Ocean acidification causes bleaching and productivity loss in coral reef builders

Anthony

Kline

Díaz-Pulido

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

1,041

894

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Ocean acidification represents a key threat to coral reefs by reducing the calcification rate of framework builders. In addition, acidification is likely to affect the relationship between corals and their symbiotic dinoflagellates and the productivity of this association. However, little is known about how acidification impacts on the physiology of reef builders and how acidification interacts with warming. Here, we report on an 8-week study that compared bleaching, productivity, and calcification responses of crustose coralline algae (CCA) and branching (Acropora) and massive (Porites) coral species in response to acidification and warming. Using a 30-tank experimental system, we manipulated CO2 levels to simulate doubling and three-to fourfold increases [Intergovernmental Panel on Climate Change (IPCC) projection categories IV and VI] relative to present-day levels under cool and warm scenarios. Results indicated that high CO2 is a bleaching agent for corals and CCA under high irradiance, acting synergistically with warming to lower thermal bleaching thresholds. We propose that CO2 induces bleaching via its impact on photoprotective mechanisms of the photosystems. Overall, acidification impacted more strongly on bleaching and productivity than on calcification. Interestingly, the intermediate, warm CO 2 scenario led to a 30% increase in productivity in Acropora, whereas high CO 2 lead to zero productivity in both corals. CCA were most sensitive to acidification, with high CO 2 leading to negative productivity and high rates of net dissolution. Our findings suggest that sensitive reef-building species such as CCA may be pushed beyond their thresholds for growth and survival within the next few decades whereas corals will show delayed and mixed responses.climate change ͉ global warming ͉ carbon dioxide ͉ Great Barrier Reef T he concentrations of atmospheric CO 2 predicted for this century present two major challenges for coral-reef building organisms (1). Firstly, rising sea surface temperatures associated with CO 2 increase will lead to an increased frequency and severity of coral bleaching events (large-scale disintegration of the critically important coral-dinoflagellate symbiosis) with negative consequences for coral survival, growth, and reproduction (2). Secondly, Ͼ30% of the CO 2 emitted to the atmosphere by human activities is taken up by the ocean (3, 4), lowering the pH of surface waters to levels that will potentially compromise or prevent calcium carbonate accretion by organisms including reef corals (1, 5), calcifying algae (6, 7) and a diverse range of other organisms (8). Ocean acidification research has focused mainly on the consequences of shifting ocean chemistry toward suboptimal saturation states of aragonite and calcite (9) and how this will affect the calcification processes of organisms in the pelagic (10) and benthic (11, 12) environments. Previous studies have shown dissolution of coral skeletons (13) and reduced rates of reef calcification (14) with increasing CO 2 concentrations. Ocea...

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Time-integrated thermal bleaching thresholds of reefs and their variation on the Great Barrier Reef

Cited by 208 publications

References 21 publications

Changes in coral-associated microbial communities during a bleaching event

Changes in coral-associated microbial communities during a bleaching event

Novel algal symbiont (Symbiodinium spp.) diversity in reef corals of Western Australia

Ocean acidification causes bleaching and productivity loss in coral reef builders

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