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Many ecosystems suffer systemwide outbreaks of damaging species propagating from primary outbreak sites. Connectivity patterns can identify parts of the ecosystem that help turn local outbreaks into a systemwide contagion through a series of transmission events. Here, we show that patterns of larval connectivity among reefs can help explain periodic crown-of-thorns starfish ( COTS) epidemics across the Great Barrier Reef ( GBR)., We simulated potential dispersal of COTS larvae to obtain a connectivity network of coral reefs across the entire GBR. Network analysis revealed areas of high local connectivity where any outbreaks could be amplified locally, as well as those areas with potential to cause large-scale epidemics with ecosystem-wide impacts., We find that the regions where COTS epidemics are known to originate are predictable from their high local and systemwide connectivity. Extensive larval exchanges among reef clusters in these regions can start a chain reaction of COTS population build-up. The same regions also have high potential to reach and affect other parts of the GBR, thereby maximizing the likelihood that any outbreaks would eventually propagate throughout the ecosystem., Hydrodynamic properties and geography of the GBR make it vulnerable to COTS epidemics. Using network analysis to identify regions with high-risk high-impact sources could help control these devastating events in future., Synthesis and applications. The observed centre of origin for COTS epidemics (the Cooktown-Cairns region) can be predicted from its elevated short- and long-range levels of larval connectivity. Connectivity analysis of per-reef risks provides spatially explicit targets to guide surveillance and control measures that might help curtail COTS epidemics through prioritization of highly connected reefs. The analytical approach developed here for COTS connectivity can also be applied to identify well-connected patches and regions in other interconnected ecological systems. [ABSTRACT FROM AUTHOR]

Summary Rising anthropogenic CO2 emissions acidify the oceans, and cause changes to seawater carbon chemistry. Bacterial biofilm communities reflect environmental disturbances and may rapidly respond to ocean acidification. This study investigates community composition and activity responses to experimental ocean acidification in biofilms from the Australian Great Barrier Reef. Natural biofilms grown on glass slides were exposed for 11 d to four controlled pCO2 concentrations representing the following scenarios: A) pre-industrial (∼300 ppm), B) present-day (∼400 ppm), C) mid century (∼560 ppm) and D) late century (∼1140 ppm). Terminal restriction fragment length polymorphism and clone library analyses of 16S rRNA genes revealed CO2-correlated bacterial community shifts between treatments A, B and D. Observed bacterial community shifts were driven by decreases in the relative abundance of Alphaproteobacteria and increases of Flavobacteriales ( Bacteroidetes) at increased CO2 concentrations, indicating pH sensitivity of specific bacterial groups. Elevated pCO2 (C + D) shifted biofilm algal communities and significantly increased C and N contents, yet O2 fluxes, measured using in light and dark incubations, remained unchanged. Our findings suggest that bacterial biofilm communities rapidly adapt and reorganize in response to high pCO2 to maintain activity such as oxygen production. [ABSTRACT FROM AUTHOR]

In the face of increasing cumulative effects from human and natural disturbances, sustaining coral reefs will require a deeper understanding of the drivers of coral resilience in space and time. Here we develop a high-resolution, spatially explicit model of coral dynamics on Australia's Great Barrier Reef (GBR). Our model accounts for biological, ecological and environmental processes, as well as spatial variation in water quality and the cumulative effects of coral diseases, bleaching, outbreaks of crown-of-thorns starfish (Acanthaster cf. solaris), and tropical cyclones. Our projections reconstruct coral cover trajectories between 1996 and 2017 over a total reef area of 14,780 km 2 , predicting a mean annual coral loss of -0.67%/year mostly due to the impact of cyclones, followed by starfish outbreaks and coral bleaching. Coral growth rate was the highest for outer shelf coral communities characterized by digitate and tabulate Acropora spp. and exposed to low seasonal variations in salinity and sea surface temperature, and the lowest for inner-shelf communities exposed to reduced water quality. We show that coral resilience (defined as the net effect of resistance and recovery following disturbance) was negatively related to the frequency of river plume conditions, and to reef accessibility to a lesser extent. Surprisingly, reef resilience was substantially lower within no-take marine protected areas, however this difference was mostly driven by the effect of water quality. Our model provides a new validated, spatially explicit platform for identifying the reefs that face the greatest risk of biodiversity loss, and those that have the highest chances to persist under increasing disturbance regimes., (© 2019 John Wiley & Sons Ltd.)

Corals of the Great Barrier Reef (GBR) have declined over the past 30 years. While reef state depends on the balance between disturbance and recovery, most studies have focused on the effects of disturbance on reef decline. We show that coral recovery rates across the GBR declined by an average of 84% between 1992 and 2010. Recovery was variable: Some key coral types had close to zero recovery by the end of that period, whereas some reefs exhibited high recovery. Our results indicate that coral recovery is sensitive to chronic but manageable pressures, and is suppressed for several years following acute disturbances. Loss of recovery capacity was partly explained by the cumulative effects of chronic pressures including water quality, warming, and sublethal effects of acute disturbances (cyclones, outbreaks of crown-of-thorns starfish, and coral bleaching). Modeled projections indicate that recovery rates can respond rapidly to reductions in acute and chronic stressors, a result that is consistent with fast recovery observed on some reefs in the central and southern GBR since the end of the study period. A combination of local management actions to reduce chronic disturbances and global action to limit the effect of climate change is urgently required to sustain GBR coral cover and diversity.

Coastal development activities can cause local increases in turbidity and sedimentation. This study characterises the spatial and temporal variability of turbidity near an inshore fringing coral reef in the central Great Barrier Reef, under a wide range of natural conditions. Based on the observed natural variability, we outline a risk management scheme to minimise the impact of construction-related turbidity increases. Comparison of control and impact sites proved unusable for real-time management of turbidity risks. Instead, we suggest using one standard deviation from ambient conditions as a possible conservative upper limit of an acceptable projected increase in turbidity. In addition, the use of regional weather forecast as a proxy for natural turbidity is assessed. This approach is simple and cheap but also has limitations in very rough conditions, when an anthropogenic turbidity increase could prove fatal to corals that are already stressed under natural conditions.