The Great Barrier Reef (the Reef) is a globally significant socio-ecological system, where human wellbeing is deeply intertwined with ecological health. An adaptive management approach underpins, and shapes coordinated management of the Reef, in the face of spatial, temporal, and stakeholder diversity combined with rapidly changing climactic conditions. Social science, specifically human dimensions research, is essential for effective adaptive management of this marine environment. To examine how human dimensions research is currently applied in Reef adaptive management, and to identify barriers and enablers to its effective integration, we conducted semi-structured interviews with 30 Reef managers and social science practitioners. Overall, findings reveal increasing value placed on human dimensions research but also an uncertainty surrounding its application and significance beyond supporting biophysical science. We recommend that understanding the current challenges and the future opportunities for human dimensions to be a key player in management decision making, can be understood through a systems lens. Specifically, we suggest that shifting Reef adaptive management, from a rigid, solution-oriented hard systems approach to a more flexible, soft systems style has the potential to enable human dimensions research to move beyond contextual support for biophysical information to meaningful contributions shaping management processes and outcomes. We demonstrate the benefits of soft systems thinking for enhancing the influence of human dimensions research in environmental decision-making and adaptive management by linking empirical insights with governance literature. We conclude with recommendations to further support this transition, aiming to strengthen the resilience and inclusivity of Reef management in the face of accelerating environmental pressures.
Effective monitoring of crown-of-thorns starfish (COTS) populations and coral cover is critical for informing management of COTS outbreaks throughout their tropical Indo-Pacific range, including Australia’s Great Barrier Reef. However, existing monitoring tools such as manta tow and cull diver surveys have well-known limitations including accuracy and resource demands. This study evaluates a range of monitoring tools for assessing both COTS and coral populations. Tools that measure both COTS and coral include manta tow surveys, scooter-assisted large area diver-based (SALAD) surveys and surveys undertaken using the ReefScan towed camera platform. For COTS-only monitoring, we examine cull diver surveys and environmental DNA (eDNA) sampling. Data from side-by-side deployments on seven to ten reefs (depending on the tool) with varying COTS densities and coral cover were collected and analysed to calibrate estimates between tools. The calibration models developed will aid in integrating data from diverse sources and facilitate the translation of estimates based on one monitoring tool to another. Critically, the models provide a means of estimating COTS density (COTS per hectare) for monitoring tools that do not directly collect this measure, allowing more meaningful decision-making around ecological thresholds and enabling threshold-based management regardless of which tool collected the data. The study emphasises that each tool has specific applications for addressing knowledge gaps and informing management decisions, advocating for an integrated, multi-tool monitoring strategy that leverages the strengths of each tool to improve the overall effectiveness and efficiency of COTS and coral monitoring.
Crustose coralline algae (CCA) comprise hundreds of different species and are critical to coral reef growth, structural stability and coral recruitment. Despite their integral role in reef functioning, little is known about the diversity and structure of bacterial communities associated with CCA. We address this knowledge gap by characterising the surface microbial communities of 15 Indo-Pacific CCA species across eight different families from the Great Barrier Reef, using 16S rRNA amplicon sequencing. CCA microbial community composition was distinct and found to primarily differentiate by algal host species. When looking at the core bacterial communities, divergence across CCA microbiomes was additionally correlated to host phylogeny. CCA from similar light environments and depths also had more similar microbial communities, suggesting the potential role of environmental parameters in influencing microbial community organisation. The fundamental descriptions of CCA bacterial communities for a wide range of Indo-Pacific species presented here provide essential baseline information to further inform CCA microbial symbiosis research.
Predator removal can destabilise and devastate ecosystems, particularly if a species released from top-down control can itself fundamentally alter the system1. On Indo-Pacific reefs, coral-eating crown-of-thorns starfish (CoTS, Acanthaster spp.) threaten ecosystem function and resilience due to their propensity to undergo destructive population outbreaks that cause widespread coral loss2,3. One of the foremost hypotheses to explain these outbreaks centres around the overfishing of their putative predators4,5. Notably, outbreaks of CoTS seem to be less prevalent on reefs protected from fishing4,5, but the risk of predation has never been quantified. Here, we show that the predation risk for CoTS inside no-take marine reserves on Australia's Great Barrier Reef is 3.6- and 2.8-times higher than in areas where fishing is permitted and limited, respectively. Moreover, the elevated predation risk inside no-take reserves is directly attributable to a single fish species, the spangled emperor (Lethrinus nebulosus), a fishery species that shows up to 6.3-times greater biomass on no-take versus fished reefs. These findings may explain how no-take reserves protect reefs from CoTS outbreaks4 and highlight targeted conservation of L. nebulosus as a promising management strategy to mitigate reef degradation by CoTS outside of no-take reserves.
Acropora is the most diverse and widespread reef-building coral genus in the world. Although known for its critical ecological role in shallow water habitats, its abundance and diversity at upper mesophotic depths have only recently been uncovered. Consequently, little is known about the genetic structuring of mesophotic Acropora populations and their potential ecological and evolutionary relationships with shallow populations. Here, we present the first population genomic evaluation of the depth-generalist coral Acropora aculeus to assess genetic structuring across depths (10 and 40 m) and regions (the Great Barrier Reef (GBR) and the Western Coral Sea (WCS)). We observed strong geographic differentiation between regions, indicating the relative isolation of WCS atolls, with some admixture from WCS into the GBR, but rarely in the opposite direction. Conversely, we observed no geographic or depth-related genetic structuring within regions, although the limited sample sizes prevented evaluation of local allelic patterns over depth. In other words, A. aculeus appears to maintain widespread connectivity within regions, consistent with its broadcast spawning reproductive mode. The lack of depth differentiation requires further assessment to evaluate the potential refuge role of mesophotic populations on isolated reefs, such as in the WCS.
