scholarly journals Large-scale interventions may delay decline of the Great Barrier Reef

2021 ◽  
Vol 8 (4) ◽  
Author(s):  
Scott A. Condie ◽  
Kenneth R. N. Anthony ◽  
Russ C. Babcock ◽  
Mark E. Baird ◽  
Roger Beeden ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Great Barrier Reef ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Coral Cover ◽  
Solar Radiation Management ◽  
Successful Implementation ◽  
Barrier Reef ◽  
Cumulative Impacts ◽  
Coral Rubble

On the iconic Great Barrier Reef (GBR), the cumulative impacts of tropical cyclones, marine heatwaves and regular outbreaks of coral-eating crown-of-thorns starfish (CoTS) have severely depleted coral cover. Climate change will further exacerbate this situation over the coming decades unless effective interventions are implemented. Evaluating the efficacy of alternative interventions in a complex system experiencing major cumulative impacts can only be achieved through a systems modelling approach. We have evaluated combinations of interventions using a coral reef meta-community model. The model consisted of a dynamic network of 3753 reefs supporting communities of corals and CoTS connected through ocean larval dispersal, and exposed to changing regimes of tropical cyclones, flood plumes, marine heatwaves and ocean acidification. Interventions included reducing flood plume impacts, expanding control of CoTS populations, stabilizing coral rubble, managing solar radiation and introducing heat-tolerant coral strains. Without intervention, all climate scenarios resulted in precipitous declines in GBR coral cover over the next 50 years. The most effective strategies in delaying decline were combinations that protected coral from both predation (CoTS control) and thermal stress (solar radiation management) deployed at large scale. Successful implementation could expand opportunities for climate action, natural adaptation and socioeconomic adjustment by at least one to two decades.

Settlement and recruitment of Acanthatser planci on the Great Barrier Reef: questions of process and scale

1992 ◽  
Vol 43 (3) ◽  
pp. 611 ◽  
Author(s):  
C Johnson
Keyword(s):  
Spatial Distribution ◽  
Great Barrier Reef ◽  
Deep Water ◽  
Large Scale ◽  
Coral Cover ◽  
Larval Settlement ◽  
Future Research ◽  
Small Scale ◽  
Barrier Reef ◽  
Coral Rubble

This paper briefly reviews information on settlement and recruitment of Acanthaster planci in the Great Barrier Reef (GBR) system, with emphasis on the recent phenomenon of population outbreaks of the starfish. Observations that recent outbreaks have occurred in two series of activity (1962-77 and 1979-91+), each characterized by a southward wave of infestations in the central section of the GBR, and that outbreaks are not preceded by observable increases in densities of juveniles, have important implications for settlement and recruitment processes. The pattern of outbreaks indicates that primary outbreaks occur infrequently and unpredictably in the vicinity of 16�s. However, it is not possible to assert that primary outbreaks have not occurred elsewhere in the GBR system, and isolated outbreaks at the southern end of the GBR may be primary events. Present data are insufficient to discern whether recruitment leading to primary outbreaks is by mass settlement of larvae or aggregation of adult starfish of various ages. In contrast, evidence indicates strongly that the majority of outbreaks in the system are secondary infestations as a result of water-borne transport and subsequent mass settlements of planktonic larvae seeded by other outbreak populations (and initially by populations undergoing primary outbreaks). The likelihood and pattern of secondary outbreaks is influenced by several parameters that operate at vastly different scales. These include passive transport of larvae by large-scale circulation patterns at scales of 104-106 m, which can largely account for the southward wave, and substratum selectivity by larvae at small scales (0-10-3 m). The spatial distribution of important cues for larval settlement (coral rubble and the coralline alga Lithothamnium pseudosorum) suggests that mass settlements are more likely to occur in deep water at the base of reefs, where they are less likely to be observed. Several foci are defined for future research on settlement and recruitment processes. These include (1) identification of parameters influencing the spatial and temporal distribution of recruitment events that initiate primary outbreaks, (2) testing of hypotheses relating to dissipation of the southward movement of outbreaks at about 20�s despite an abundance of reefs in the area supporting high coral cover, (3) determining the period of competency of larvae for settlement, (4) elucidating the behaviour of larvae (particularly late brachiolaria) in the water column, (5) further work to identify substrata inductive of larval settlement and to determine the nature of inducers, the spatial distribution of inductive substrata, and the effect of small-scale hydrodynamic processes in modifying the response of larvae to inductive substrata, and (6) testing of the hypothesis of deep-water recruitment.

scholarly journals Cumulative impacts across Australia’s Great Barrier Reef: A mechanistic evaluation

2020 ◽  
Author(s):  
Yves-Marie Bozec ◽  
Karlo Hock ◽  
Robert A. B. Mason ◽  
Mark E. Baird ◽  
Carolina Castro-Sanguino ◽  
...  
Keyword(s):  
Water Quality ◽  
Life History ◽  
Great Barrier Reef ◽  
Community Dynamics ◽  
Multiple Stressors ◽  
Coral Cover ◽  
Environmental Data ◽  
Environmental Drivers ◽  
Barrier Reef ◽  
Cumulative Impacts

ABSTRACTCumulative impacts assessments on marine ecosystems have been hindered by the difficulty of collecting environmental data and identifying drivers of community dynamics beyond local scales. On coral reefs, an additional challenge is to disentangle the relative influence of multiple drivers that operate at different stages of coral ontogeny. We integrated coral life history, population dynamics and spatially-explicit environmental drivers to assess the relative and cumulative impacts of multiple stressors across 2,300 km of the world’s largest coral reef ecosystem, Australia’s Great Barrier Reef (GBR). Using literature data, we characterized relationships between coral life history processes (reproduction, larval dispersal, recruitment, growth and mortality) and environmental variables. We then simulated coral demographics and stressor impacts at the organism (coral colony) level on >3,800 individual reefs linked by larval connectivity, and exposed to temporally- and spatially-realistic regimes of acute (crown-of-thorns starfish outbreaks, cyclones and mass coral bleaching) and chronic (water quality) stressors. Model simulations produced a credible reconstruction of recent (2008–2020) coral trajectories consistent with monitoring observations, while estimating the impacts of each stressor at reef and regional scales. Overall, corals declined by one third across the GBR, from an average ∼29% to ∼19% hard coral cover. By 2020, less than 20% of the GBR had coral cover higher than 30%. Global annual rates of coral mortality were driven by bleaching (48%) ahead of cyclones (41%) and starfish predation (11%). Beyond the reconstructed status and trends, the model enabled the emergence of complex interactions that compound the effects of multiple stressors while promoting a mechanistic understanding of coral cover dynamics. Drivers of coral cover growth were identified; notably, water quality (suspended sediments) was estimated to delay recovery for at least 25% of inshore reefs. Standardized rates of coral loss and recovery allowed the integration of all cumulative impacts to determine the equilibrium cover for each reef. This metric, combined with maps of impacts, recovery potential, water quality thresholds and reef state metrics, facilitates strategic spatial planning and resilience-based management across the GBR.

scholarly journals Potential for rapid genetic adaptation to warming in a Great Barrier Reef coral

2017 ◽  
Author(s):  
Mikhail V. Matz ◽  
Eric A. Treml ◽  
Galina V. Aglyamova ◽  
Madeleine J. H. van Oppen ◽  
Line K. Bay
Keyword(s):  
Genetic Variation ◽  
Great Barrier Reef ◽  
Coral Cover ◽  
Reef Coral ◽  
Biophysical Model ◽  
Detectable Effect ◽  
Genetic Adaptation ◽  
Barrier Reef ◽  
Biophysical Modeling ◽  
Adaptive Genetic Variation

AbstractCan genetic adaptation in reef-building corals keep pace with the current rate of sea surface warming? Here we combine population genomic, biophysical modeling, and evolutionary simulations to predict future adaptation of the common coralAcropora milleporaon the Great Barrier Reef. Loss of coral cover in recent decades did not yet have detectable effect on genetic diversity in our species. Genomic analysis of migration patterns closely matched the biophysical model of larval dispersal in favoring the spread of existing heat-tolerant alleles from lower to higher latitudes. Given these conditions we find that standing genetic variation could be sufficient to fuel rapid adaptation ofA. milleporato warming for the next 100-200 years, although random thermal anomalies would drive increasingly severe mortality episodes. However, this adaptation will inevitably cease unless the warming is slowed down, since no realistic mutation rate could replenish adaptive genetic variation fast enough.

scholarly journals Long-term shifts in the colony size structure of coral populations along the Great Barrier Reef

2020 ◽  
Vol 287 (1936) ◽  
pp. 20201432
Author(s):  
Andreas Dietzel ◽  
Michael Bode ◽  
Sean R. Connolly ◽  
Terry P. Hughes
Keyword(s):  
Great Barrier Reef ◽  
Colony Size ◽  
Size Structure ◽  
Coral Cover ◽  
Spatial Scales ◽  
Reproductive Capacity ◽  
Barrier Reef ◽  
Size Frequency Distribution ◽  
Coral Colony ◽  
Recovery Potential

The age or size structure of a population has a marked influence on its demography and reproductive capacity. While declines in coral cover are well documented, concomitant shifts in the size-frequency distribution of coral colonies are rarely measured at large spatial scales. Here, we document major shifts in the colony size structure of coral populations along the 2300 km length of the Great Barrier Reef relative to historical baselines (1995/1996). Coral colony abundances on reef crests and slopes have declined sharply across all colony size classes and in all coral taxa compared to historical baselines. Declines were particularly pronounced in the northern and central regions of the Great Barrier Reef, following mass coral bleaching in 2016 and 2017. The relative abundances of large colonies remained relatively stable, but this apparent stability masks steep declines in absolute abundance. The potential for recovery of older fecund corals is uncertain given the increasing frequency and intensity of disturbance events. The systematic decline in smaller colonies across regions, habitats and taxa, suggests that a decline in recruitment has further eroded the recovery potential and resilience of coral populations.

Larval dispersal simulations: correlation with the crown-of-thorns starfish outbreaks database

1992 ◽  
Vol 43 (3) ◽  
pp. 569 ◽  
Author(s):  
MK James ◽  
JP Scandol
Keyword(s):  
Great Barrier Reef ◽  
Larval Dispersal ◽  
Large Scale ◽  
Numerical Models ◽  
Temporal Distribution ◽  
Research Programme ◽  
Strong Positive Correlation ◽  
Barrier Reef ◽  
Central Hypothesis ◽  
Scale Population

The work reported in this paper is a further development of results from a research programme whose principal objective is to achieve an understanding of the large-scale population dynamics of Acanthaster planci. The research is based on the development and use of numerical models of hydrodynamics and resulting larval dispersal throughout a large portion of the Great Barrier Reef. It is chiefly concerned with the large-scale statistical patterns of larval dispersal, the central hypothesis being that passive hydrodynamic dispersal plays an important role in the recruitment process. The present aim is to examine more closely than has been done before the consistencies between the modelling results and the database of recorded observations of crown-of-thorns starfish outbreaks. Reefs in the Cairns and Central Sections of the Great Barrier Reef Marine Park that were recorded as carrying active outbreaks during the period 1979-89 were used as sources in a programme of intensive simulations of Acanthaster larval dispersal under forcing by the wind, tidal action and the East Australian Current. The resulting broad-scale patterns of larval dispersal were found to be in strong qualitative agreement with the observed spatial and temporal distribution of adult Acanthaster populations. Statistical analysis of the results revealed a strong positive correlation between potential recruitment on surveyed reefs, as estimated by the dispersal simulations, and the observed presence of outbreak populations on those reefs. The correlation was particularly strong when different cross-shelf zones were considered separately.

scholarly journals Cross-Shelf Variation Among Juvenile and Adult Coral Assemblages on Australia’s Great Barrier Reef

Diversity ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 85 ◽  
Author(s):  
Michelle J. Jonker ◽  
Angus A. Thompson ◽  
Patricia Menéndez ◽  
Kate Osborne
Keyword(s):  
Great Barrier Reef ◽  
Coral Cover ◽  
Synergistic Effects ◽  
Outer Shelf ◽  
Lower Latitude ◽  
Barrier Reef ◽  
Hard Coral ◽  
Coral Abundance ◽  
The Status ◽  
Community Types

Coral reefs are under increasing pressure from a variety of stressors, highlighting the need for information about the status of coral reef communities including the distribution, abundance and composition of juvenile and adult coral assemblages. This information is currently limited for the Great Barrier Reef (GBR) and is necessary for understanding the impacts of disturbances and the system’s potential for recovery. This study reports juvenile and adult hard coral abundance and composition from 122 reefs on the GBR during a period of limited acute disturbance. The data represent baseline observations for juvenile hard coral assemblages spanning the longitudinal cross-shelf gradient of the GBR and 12 degrees of latitude and augment reported distribution of adult coral assemblages over the same scale with inclusion of additional reefs. Juvenile and adult coral assemblages reflected broad differences imposed by the gradient of environmental conditions across the GBR. The mean density of juvenile hard corals was lower in the inshore reefs (5.51 m2) than at either the mid-shelf (11.8 m2) or outer shelf reefs (11.2 m2). The composition of juvenile and adult coral assemblages covaried overall, although there were different relationships between these two life stages across the continental shelf and among community types. Dissimilarity between juvenile and adult coral assemblages was greater on inshore and outer shelf reefs than on reefs in the mid-shelf, although, there were differences in community types both within these shelf positions and those that spanned mid- and outer shelf reefs. Dissimilarity was greatest for Inshore branching Acropora and high for Southern Acropora communities, although very high coral cover and very low juvenile densities at these reefs precluded interpretation beyond the clear competitive dominance of Acropora on those reefs. Dissimilarity was also high between juvenile and adult coral assemblages of Turbid inshore communities suggesting water quality pressures, along with synergistic effects of other stressors, pose ongoing selective pressures beyond the juvenile stage. Conversely, relatively low dissimilarity between juvenile and adult coral assemblages on mid-shelf and lower latitude outer shelf reefs suggests pressures beyond those influencing settlement and early post-settlement survival were having less influence on the composition of adult coral assemblages.

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