Changes in disturbance regimes due to climate change are increasingly challenging the capacity of ecosystems to absorb recurrent shocks and reassemble afterwards, escalating the risk of widespread ecological collapse of current ecosystems and the emergence of novel assemblages1,2,3. In marine systems, the production of larvae and recruitment of functionally important species are fundamental processes for rebuilding depleted adult populations, maintaining resilience and avoiding regime shifts in the face of rising environmental pressures4,5. Here we document a regional-scale shift in stock–recruitment relationships of corals along the Great Barrier Reef—the world’s largest coral reef system—following unprecedented back-to-back mass bleaching events caused by global warming. As a consequence of mass mortality of adult brood stock in 2016 and 2017 owing to heat stress6, the amount of larval recruitment declined in 2018 by 89% compared to historical levels. For the first time, brooding pocilloporids replaced spawning acroporids as the dominant taxon in the depleted recruitment pool. The collapse in stock–recruitment relationships indicates that the low resistance of adult brood stocks to repeated episodes of coral bleaching is inexorably tied to an impaired capacity for recovery, which highlights the multifaceted processes that underlie the global decline of coral reefs. The extent to which the Great Barrier Reef will be able to recover from the collapse in stock–recruitment relationships remains uncertain, given the projected increased frequency of extreme climate events over the next two decades7.
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Source data on reef locations, adult coral abundance, recruit densities and coral reproductive condition before and after bleaching are available online at the Tropical Data Hub (https://tropicaldatahub.org/ with DOI: 10.25903/5c81fc323d129).
Computer code for statistical analyses is available from the corresponding author on request.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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We acknowledge support from the Australian Research Council’s Centre of Excellence Program (CE140100020). We thank the many dozens of student volunteers and technicians who assisted with this research over three decades.
Nature thanks James Guest, Peter Sale and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
Extended Data Fig. 1 Frequency distribution of the density of coral recruits, before and after mass bleaching in 2016 and 2017.
In total, 1,784 settlement panels were deployed before mass bleaching (in 1996, 1997, 1998, 2004 and 2014–2016) on 47 reefs, and 977 panels on 17 reefs after mass bleaching in2017–2018. Figure 1 shows the reef locations.
The shared lettering (A–C) indicates recruit densities in each year that are statistically indistinguishable, based on an analysis of variance with Bonferroni-corrected Tukey’s post hoc test. Horizontal lines show the median, boxes indicate the middle two quartiles, vertical lines indicate the first and fourth quartiles, and data points are outliers. a, Box plots show recruit density per settlement panel (n = 30, 55, 44, 125, 126 and 118 panels in 1996, 1997, 1998, 2016, 2017 and 2018, respectively) on Lizard Island Reef in the northern Great Barrier Reef, before and after mass mortality of established corals in March 2016 (after the retrieval of settlement panels in January 2016). Most values for 2017 are zero, causing the box plots to collapse. b, Box plots show average recruit density per panel on the Great Barrier Reef in 1996, 1997 and 2018 (n = 15 reefs per year, in 5 latitudinal sectors). The same 15 reefs were resampled in 1996 and 2018; see Fig. 1c.
Related to Fig. 2b, showing the shift in the taxonomic composition of coral recruits.
Extended Data Fig. 4 Changes in the density of coral recruits as a function of the loss or gain of adult corals.
Data points represent the change in recruitment and coral cover, shown as log10(change in recruitment) and log10(change in cover), respectively, on each of five sectors arrayed along the length of the Great Barrier Reef. Blue lines represent the linear model fits and grey shading represents 95% confidence intervals. a, Spawners. b, Brooders. Figure 3 shows the reef-scale relationships.
Extended Data Fig. 5 Coral reproductive condition on the Great Barrier Reef before mass spawning in November 1995 and 2017.
Data in each year were collected from the same set of ten reefs in five latitudinal sectors. Horizontal lines show the median percentage of spawning Acropora corals that were gravid on each reef. Boxes indicate the middle two quartiles, vertical lines indicate the first and fourth quartiles. Reef locations are provided in the source data (available online at the Tropical Data Hub).