From exposure to risk: Novel experimental approaches to analyse cumulative impacts and determine thresholds in the Great Barrier Reef World Heritage Area (GBRWHA)

Sven Uthicke

Led by: Dr Sven Uthicke, AIMS


Project Summary

Understanding cumulative impacts from multiple stressors will be critical for successful management of the Great Barrier Reef (GBR) under the Reef2050 Plan. We will produce experimental analyses of concentration-response relationships for selected species under broad, controlled envelopes of local stressors at different climate scenarios. Results will inform assessments of ecological risks, and management opportunities for a range of activities in the coastal zone and on the GBR. In a project-extension we will use exposure maps and ecological models, based on our developed and existing databases and experimental results, to advance our understanding of the contribution of individual disturbances in a cumulative framework (including both acute and chronic disturbances) to the current status of the reef. In turn, this new knowledge will inform management on setting future water quality thresholds, identifying catchments and regions as priorities for management action aimed at ameliorating impacts to reef health and building resilience for large-scale cumulative disturbances.

Project Description

The problem

  • Cumulative impacts result from one or more stressors and their interactions can accumulate in time and space, posing a threat to ecosystem resilience. Cumulative impacts represent added ecological risks and potential surprises not accounted for in conventional risk assessments. Inshore environments in the GBR are high-risk candidates for cumulative impacts as they are exposed to land-based and coastal development activities impacting water quality in addition to regional and global pressures from climate change.
  • While reef managers recognize that cumulative impacts are an added risk dimension, large knowledge gaps exist in our understanding of the effect of individual stressors on key reef species, the interplay of local and global stressors and the way individual stressors combine into cumulative impacts.
  • There is wide acceptance that improvement in water quality will ‘buy time’ for reefs to acclimatize to a warming climate and increasing ocean acidification, yet it is still unclear whether current water quality targets, are set at the right level to achieve this outcome of increased reef resilience under climate change.
  • The National Seas Simulator (SeaSim) facility in Townsville now allows us to investigate such complex interactions using sophisticated state-of-the art system controls. In SeaSim we can control cumulative exposures of sensitive marine organisms and processes under highly controlled yet environmentally relevant settings in an unprecedented way. We can therefore address and fill some of these key knowledge gaps on cumulative impacts far more efficiently than was possible in the past.
  • While previous research on cumulative impacts on the GBR has provided relevant data to inform the issue, few have followed an end-to-end pathway resulting in direct implementation and improvements to policy.

How Research Addresses Problem/Achieved outcomes of original project

  • This collaboration started with a 6-month NESP investment (project 1.6) as a gap analysis and to develop the foundational framework for prioritization of end point measurements, and building on the risk priorities defined in the Great Barrier Reef Marine Park Authority’s (GBRMPA) Outlook Report.
  • During the last 2.5 yrs (NESP 2.1.6) conducted multiple experiments on sediments, light and pesticides as local stressors and quantified their cumulative effects with climate scenarios (including climate-adjusted thresholds) for tropical coral reef species. We explored the concept of applying species-sensitivity curves to temperature for the first time in a coral reef context, and created a literature database available for adjusting pesticide guideline to account for thermal stress. Based on monitoring data and other sources (e.g. eReefs, eAtlas) we produced maps for individual stressors and explored techniques to combine those into cumulative exposure maps. Exposure layers, stressors and benthic reef data have been brought together in an ecological model which can be used to test how individual stressors interact in a cumulative fashion.
  • We investigated novel ways to assess combined risks on sensitive marine organisms and ecological processes, and will use concentration-response studies to determine climate adjusted exposure thresholds. One factsheet produced and > 10 scientific publications published.
  • Two stakeholder workshops were conducted, several workshops from other NESP projects attended. Frequent meetings with individual stakeholders at GBRMPA and the Office of the Great Barrier Reef (OGBR).
  • The findings will facilitate the development of more realistic GBR-wide exposure maps to identify acceptable and unacceptable risks for ecosystem integrity. These will be done for present day conditions and for some selected pressures under future climate scenarios, in collaboration with eAtlas. The thresholds and exposure maps will support integrated monitoring and assessments, including the adequacy of current targets for priority river pollutants.
  • An interactive tool to illustrate principals of cumulative impact and effects of land runoff under certain climate scenarios will be developed and made publically available. This tool will be developed so that findings from other NESP projects (e.g. Benthic Light, Bleaching Sensitivity along a water quality gradient) can be incorporated and communicated effectively to stakeholders. This tool will allow environmental managers to learn about key concepts in cumulative impacts, what the experimental results of the project mean and be able to investigate the model results that breakdown historic cumulative pressures on reefs based on coral functional types and water quality scenarios. This tool will be integrated with the eAtlas.


  1. To fill important experimental and conceptual gaps in understanding cumulative impacts on coral reef environments.
  2. To provide climate-adjusted thresholds for key stressors and key organisms
  3. To support cumulative risk analyses for selected key areas of the GBR
  4. To provide guidance for how exposure and risk should be analysed and mapped to inform:
    1. Spatial risk assessments of cumulative impacts on key species underpinning reef ecosystem health, resilience and outstanding universal values;
    2. Assessments of targeted risk mitigation associated with development proposals;
    3. Indicator development to monitor early warnings of cumulative impacts.


The project will use a staged approach with key identifiable and reportable and deliverable milestones at each stage:

  1. Based on synthesis and gap analysis of cumulative impacts and thresholds conducted under NESP1-1.6, the project will select key experimental variables and environmental envelopes.
  2. Conduct series of targeted short-term and longer-term experimental studies in SeaSim, using both highly replicated small-system designs and mesocosms, to improve our understanding of how the chosen indicator responses respond to multi-variate environmental scenarios of varying (short-term acute as well as chronic) exposures to sediments, turbidity, light, and temperature.
  3. Analyse multiple experimental response functions using non-linear regressions (surface fitting) to identify (1) critical thresholds for cumulative stress, (2) which stressor combinations represent the highest risks, and (3) which management actions could best alleviate stress and achieve safe distance from critical thresholds.
  4. Integration of experimental data and observational field data (Marine Monitoring Program/Long Term Monitoring Program) with eReefs and other environmental data to produce spatial/temporal exposure maps for selected field sites. Maps used to develop an interactive tool based on eAtlas which will effectively communicate to stakeholders the implications and extent of their potential actions, and how these may influence the health of the reefs in the GBR.

During the 18 month extension the project will

  • Apply our databases on species sensitivity distributions (SSD) for temperature stress to predict climate-adjusted toxicity thresholds of pesticides to tropical marine coral reef communities.
  • Continue further studies on the cumulative effects of water quality (e.g. sedimentation and light limitation) on coral under different climate conditions, and summarise findings in risk maps under three climate scenarios.
  • Analyse the influence of cumulative impacts on reef health trajectory using ecological models to identify levers that can be influenced by local management.
  • Develop an interactive on-line tool to deliver content to managers in an engaging and informative way, allowing them to explore the consequences of alternate management interventions. This tool will leverage existing capabilities in the eAtlas platform, along with new work developed as part of the Reef Integrated Monitoring and Reporting Program (RIMReP) and the Great Barrier Reef Foundation (GBRF) Reef Resilience Program. These tools will be tailored to deliver the content developed by this project.
  • Collate additional exposure maps for the last 30 years of exposure of the GBR to acute disturbances (1985 – 2018). Some of these maps have already been delivered to GBRMPA for the Fortunate Reefs projects. Data underlying the maps have been shared and are being used by scientists from the Marine Biodiversity hub for modelling. These maps will ultimately also be delivered as part of the on-line interactive tool in eAtlas
  • Produce threshold exposure maps for climate scenarios (e.g. Representative Concentration Pathways [RCP] 8.5) for 2050 and 2100 by combining experimental results with future climate predictions and present day exposure maps. These maps will ultimately also be delivered as part of the interactive tool.
  • Refine targeted research outputs through consultation with end users (OGBR and GBRMPA) to ensure a direct pathway for integration into end-user models and reporting. This will occur at the start and during the duration of the project and include a final dissemination of outputs on cumulative risk assessments to a broader group of key stakeholders.
  • Enhance collaboration between various NESP projects (e.g., Tropical Water Quality Hub: 3.3.1 Quantifying the linkages between water quality and the thermal tolerance of GBR coral reefs; Marine Biodiversity hub: Theme C Understanding pressures on the marine environment) and other projects addressing cumulative impacts by conducting an integration workshop with project leaders and staff. This workshop will be targeted at sharing experience and data and integrating outputs from different ecological models.

Links with other projects and hubs

eAtlas: All data will be lodged in eAtlas and eAtlas will be used to deliver the interactive tool.

NESP 2.3.1.: Benthic light as ecologically-validated GBR-wide indicator for water quality: drivers, thresholds and cumulative risks. Our project will use the produced light exposure maps as a predictor in the ecological models and exposure maps of this project.

NESP 3.3.1: Quantifying the linkages between water quality and the thermal tolerance of GBR coral reefs. The modelling team from our project will collaborate with Neal Cantin on this NESP project. We currently discuss inclusion of project outcomes into the interactive tool.

NESP 4.5 and 4.6 only started up and we will have discussions with the Project leader to integrate the projects. In addition, all NESP project leaders involved in cumulative impact work will be invited to our integration workshop.

Marine Biodiversity Hub: Themes C/E: Projects: E1 – (Guidelines for analysis of cumulative impacts and risks to the Great Barrier Reef) and C1 (Improving our understanding of pressures on the marine environment). Project staff have held in depth discussions with members of this project, and joined two workshops conducted by Theme C. Exposure maps and LTMP data recently supplied to project staff of project E1 for a collaborative project that will investigate the indirect effects of cumulative impacts on fish populations of the GBR.

Northern Australia Environmental Resources Hub: We recently started discussions with Dr Chris Brown about collaboration on modelling cumulative impacts, this collaboration will integrate efforts to improve our understanding of cumulative impacts from freshwater systems, to estuaries, to coastal waters and to the outer reef.

eReefs: We will summarise and use several parameters modelled in eReefs as exposure maps in our interactive online tool.

GBRMPA Fortunate Reefs: We supplied several exposure maps to this project.

GBRMPA cumulative impact Policy: Our initial work (e.g. report from NESP 1.6) stakeholder workshops at GBRMPA helped to inform the policy which is not published. The work of this project and the extension help will assist GBRMPA to implement the policy.


NESP 2017 Research Priority Alignment

This project has a strong alignment with the following Ministers and NESP Research Plan priorities:

The Ministers priorities:

Theme 1: Improved understanding of the impacts, including cumulative impacts, and pressures on priority freshwater, coastal and marine ecosystems and species.

1.4 Improve our knowledge of cumulative pressures on environmental and social values of the Great Barrier Reef to determine more effective management actions.

  • Develop better capacity to predict ecosystem decline due to cumulative pressures to guide planning and management practices.
  • Determine critical ecosystem thresholds for cumulative stress to guide environmental decision-making and policy under coastal development scenarios.
  • Identify environmental stress indicators for key reef species and habitats to support cumulative impact assessments.

Research Plan 2 priorities:

Priority 1G: Methods for assessing cumulative impacts from human activities and measures/approaches for ensuring a net environmental benefit.

As a secondary focus, the project also addresses: Priority 2A: Developing effective and cost-effective catchment and marine water quality indicators, thresholds and sub-lethal health-indicators for key marine organisms and processes in support of the Reef Integrated Monitoring Program.

Project Keywords

Cumulative impacts; Environmental risk; Thresholds.

Project Funding

This project is jointly funded through AIMS and the Australian Government’s National Environmental Science Program.

Project Publications