Cumulative impacts across Australia’s Great Barrier Reef: a mechanistic evaluation

Bozec, Yves‐Marie; Hock, Karlo; Mason, Robert A. B.; Baird, Mark E.; Castro‐Sanguino, Carolina; Condie, Scott A.; Puotinen, Marji; Thompson, Angus; Mumby, Peter J.

doi:10.1002/ecm.1494

Cited by 24 publications

(81 citation statements)

References 140 publications

(180 reference statements)

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“…The magnitude of thermal stress upon GBR corals intensifies dramatically over time, particularly under scenarios that exclude strong international efforts to tackle climate change (SSP3‐7.0; Riahi et al, 2017) or assume an energy‐intensive fossil‐based economy (SSP5‐8.5; Figure 1a; O’Neill et al, 2016; Riahi et al, 2017). These scenarios lead to a three to fourfold increase in the magnitude of thermal stress upon corals (Figure 1a) compared to the worst of recent bleaching events, which have already caused mass mortality on many GBR reefs (Bozec et al, 2021; Hughes et al, 2018). In contrast, long‐term projections under a scenario built around global collaboration on climate policy targeting mean warming above preindustrial of 2° (SSP1‐2.6; Riahi et al, 2017), or a scenario which embraces large net negative emissions to limit warming to 1.5° (SSP1‐1.9; O’Neill et al, 2016; Riahi et al, 2017), lead to far smaller increases in absolute stress.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, any reduction in the frequency of bleaching events is likely to be beneficial, particularly if their magnitude remains under 8 DHW. Thus, although the average benefit of moving to 1.5° warming rather than 2°, is a reduction of two bleaching events per decade, the existence of substantial spatial and temporal variation means that some reefs will experience longer recovery periods between events (Bozec et al, 2021; Cheung et al, 2021). This is because not all reefs bleach during a given event (Hughes, Kerry, et al, 2018; Mumby et al, 2011) and many acute disturbances are temporally clustered giving longer recovery periods (Mumby et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

“…To calculate coral stress, two metrics were applied to the sea surface temperature output: DHW and the frequency of severe bleaching years. The DHW values are a potential trigger for coral bleaching and have been strongly correlated to bleaching events in the past (Bozec et al, 2021; Hughes, Anderson, et al, 2018; Hughes et al, 2017; Skirving et al, 2020), but do not necessarily provide evidence of coral bleaching. The DHW values were calculated using the National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch methodology described below (Heron et al, 2014; Skirving et al, 2020).…”

Section: Methodsmentioning

confidence: 99%

“…Within the tropical oceans, periods of anomalously warm sea temperatures have increased in frequency (Eakin et al, 2010; Hughes, Kerry, et al, 2018; Skirving et al, 2019) and severity, resulting in the deterioration of global coral ecosystems (Wilkinson & Souter, 2008). Recent mass coral bleaching events on the GBR (1998, 2002, 2016, 2017, 2020) occurred as a result of thermal stress (Bozec et al, 2021; Eakin et al, 2010; Great Barrier Reef Marine Park Authority, 2019; Hughes, Kerry, et al, 2018; Hughes et al, 2017), often after several weeks of temperatures exceeding their usual summer temperature by 1–2°C (Berkelmans & Willis, 1999; Glynn & D’croz, 1990; Reaser et al, 2000). The term ‘bleaching’ refers to the breakdown of the relationship between corals and their photosynthetic symbiont, zooxanthellae, more commonly under radiative stress associated with higher temperatures (Enríquez et al, 2005; Jokiel & Coles, 1990).…”

Section: Introductionmentioning

confidence: 99%

“…Corals were impacted throughout the entire GBR by the 2017 and 2020 events while the 2016 event was mainly concentrated in the far north and northern GBR (Hughes et al, 2017). The impact of these recent events on corals has been unprecedented with estimated losses of coral ranging from 30% across the entire GBR (Bozec et al, 2021) to 50% in shallow waters after the 2016 event alone (Hughes et al, 2017). Moreover, Cheung et al (2021) estimated that the average supply of coral larvae to reefs could have declined by 70% (Cheung et al, 2021).…”

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confidence: 99%

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The importance of 1.5°C warming for the Great Barrier Reef

McWhorter

Halloran

Roff

et al. 2021

Global Change Biology

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Tropical coral reefs are among the most sensitive ecosystems to climate change and will benefit from the more ambitious aims of the United Nations Framework Convention on Climate Change's Paris Agreement, which proposed to limit global warming to 1.5° rather than 2°C above pre‐industrial levels. Only in the latest Intergovernmental Panel on Climate Change focussed assessment, the Coupled Model Intercomparison Project phase 6 (CMIP6), have climate models been used to investigate the 1.5° warming scenario directly. Here, we combine the most recent model updates from CMIP6 with a semi‐dynamic downscaling to evaluate the difference between the 1.5 and 2°C global warming targets on coral thermal stress metrics for the Great Barrier Reef (GBR). By ~2080, severe bleaching events are expected to occur annually under intensifying emissions (shared socioeconomic pathway SSP5‐8.5). Adherence to 2° warming (SSP1‐2.6) halves this frequency but the main benefit of confining warming to 1.5° (SSP1‐1.9) is that bleaching events are reduced further to 3 events per decade. Attaining low emissions of 1.5° is also paramount to prevent the mean magnitude of thermal stress from stabilizing close to a critical thermal threshold (8 Degree Heating Weeks). Thermal stress under the more pessimistic pathways SSP3‐7.0 and SSP5‐8.5 is three to fourfold higher than the present day, with grave implications for future reef ecosystem health. As global warming continues, our projections also indicate more regional warming in the central and southern GBR than the far north and northern GBR.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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The importance of 1.5°C warming for the Great Barrier Reef

McWhorter

Halloran

Roff

et al. 2021

Global Change Biology

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Increasing disturbance frequency undermines coral reef recovery

Emslie,

Logan,

Bray

et al. 2024

Ecological Monographs

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Climate‐driven alterations to disturbance regimes are increasingly disrupting patterns of recovery in many biomes. Here, we examine the impact of disturbance and subsequent level of recovery in live hard coral cover on the Great Barrier Reef (GBR) across the last three decades. We demonstrate that a preexisting pattern of infrequent disturbances of limited spatial extent has changed to larger and more frequent disturbances, dominated by marine heatwaves and severe tropical cyclones. We detected an increase in the impact (measured as coral loss) across 265 individual disturbance impacts on 131 reefs in a 36‐year dataset (1985–2022). Additionally, the number of survey reefs impacted by disturbance has increased each decade from 6% in the 1980s to 44% in the 2010s, as has the frequency of mass coral bleaching across the GBR, which has increased between 19% and 28% per year, and cyclones (3%–5% per year), resulting in less time for recovery. Of the 265 disturbance impacts we recorded, complete recovery to the highest levels of coral cover recorded earlier in this study (the “historical benchmark”) occurred only 62 (23%) times. Of the 23% of disturbance impacts that resulted in complete recovery to historical benchmarks, 34/62 recovered to their benchmark in 2021 or 2022. Complete recovery was more likely when the historical benchmark was <25% live hard coral cover. The lack of recovery was attributed to recovery time windows becoming shorter due to increases in the frequency of cyclones and of thermal stress events that result in mass coral bleaching episodes. These results confirm that climate change is contributing to ecosystem‐wide changes in the ability of coral reefs to recover.

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Control efforts of crown‐of‐thorns starfish outbreaks to limit future coral decline across the Great Barrier Reef

et al. 2023

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Crown‐of‐thorns starfish (CoTS) naturally occur on coral reefs throughout the Indo‐Pacific region. On Australia's Great Barrier Reef (GBR), outbreaks of CoTS populations are responsible for ecologically significant losses of corals, and while they have been documented for decades, they now undermine coral recovery from multiple stressors, especially anthropogenic warming. Culling interventions are currently the best approach to control CoTS outbreaks on the GBR, but assessing control effectiveness under multiple stressors is complicated. Using an ensemble of two reef community models simulating the temporal and spatial dynamics of CoTS and corals under future climate scenarios, we evaluate the present‐day and future effectiveness of the current implementation of the GBR CoTS Control Program. Specifically, we determine the culling effort needed (i.e., number of vessels) to achieve the maximum ecological benefits as predicted by the models under possible warming futures. Benefits were measured by comparing projections of coral cover and CoTS densities under scenarios of increasing control effort and baseline scenarios where no control was simulated. Projections of present‐day control efforts (five vessels) show that the number of individual reefs subject to CoTS outbreaks is reduced by 50%–65% annually, yielding a benefit of 5%–7% of healthy GBR coral area per decade, equivalent to gaining 104–150 km2 of live corals by 2035. A threefold increase in current control efforts is sufficient to reach more than 80% of the maximum coral benefits predicted by each model, but the future amount of effort required to control CoTS effectively depends on the intensity of warming and the early detection of CoTS outbreaks. While culling CoTS across the entire GBR is unfeasible, we provide a framework for maximizing ecosystem‐wide benefits of CoTS control and guide management decisions on the required culling effort needed to reduce CoTS outbreaks to levels that may ensure coral persistence in the face of future climate change impacts.

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Cumulative impacts across Australia’s Great Barrier Reef: a mechanistic evaluation

Cited by 24 publications

References 140 publications

The importance of 1.5°C warming for the Great Barrier Reef

The importance of 1.5°C warming for the Great Barrier Reef

Increasing disturbance frequency undermines coral reef recovery

Control efforts of crown‐of‐thorns starfish outbreaks to limit future coral decline across the Great Barrier Reef

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