Supporting resilience-based coral reef management using broadscale threshold approaches – Nature

 

Report on the Resilience-Based Management of Coral Reefs at Aldabra Atoll in Alignment with Sustainable Development Goals

Executive Summary

This report details a study assessing the resilience of coral reefs at Aldabra Atoll, a remote UNESCO Marine World Heritage Site, through the lens of Resilience-Based Management (RBM). The assessment aligns with key United Nations Sustainable Development Goals (SDGs), particularly SDG 14 (Life Below Water) and SDG 13 (Climate Action). Using reef survey data from 2014-2015, the study evaluated key resilience indicators against established broadscale thresholds. Findings indicate that the seaward reefs of Aldabra exhibit high resilience, characteristic of a well-managed marine reserve, thereby contributing significantly to SDG 14 targets. A composite resilience index was developed, and reefs were classified into management strategies (‘protect’, ‘recover’, ‘transform’) to guide future actions. The resilience scores were contextualized by tracking coral cover recovery following the 2016 global bleaching event. The results affirm that current management, including the regulation of human activity, effectively supports reef health. The report recommends enhancing future assessments by integrating site-specific factors and expanding the range of threshold categories to further strengthen adaptive management and progress towards global sustainability targets.

Introduction: Aligning Coral Reef Management with Sustainable Development Goals

The escalating impacts of climate change, a core concern of SDG 13 (Climate Action), are causing rapid transformations in coral reef ecosystems worldwide. This has necessitated a paradigm shift in conservation from preserving static systems to maintaining ecosystem function and maximizing resilience. This approach, known as Resilience-Based Management (RBM), directly supports the objectives of SDG 14 (Life Below Water), specifically Target 14.2, which calls for the sustainable management and protection of marine ecosystems to strengthen their resilience.

The Imperative for Resilience-Based Management

RBM provides a framework for managing ecosystems in the face of disturbances. Its successful implementation relies on:

• Clear articulation of management objectives.
• Identification of robust indicators to monitor ecosystem functions.
• Establishment of clear reference thresholds for these indicators.

However, a significant challenge for many marine managers is the lack of localized, long-term data needed to establish site-specific thresholds. This study addresses this gap by applying published, broadscale thresholds to assess reef condition at Aldabra Atoll, providing a model for data-limited regions to advance towards their SDG 14 commitments.

Study Objectives and Contribution to SDGs

This study utilizes pre-bleaching event data (2014-2015) from Aldabra Atoll to achieve three primary objectives, each contributing to the evidence base for sustainable ocean management:

1. Assess the relative resilience of Aldabra’s reefs by comparing local indicator data to broadscale scientific thresholds.
2. Synthesize these indicators into a composite resilience index for each site to provide a clear, comparative metric for managers.
3. Classify reefs into management strategies (‘protect’, ‘recover’, ‘transform’) to guide targeted, evidence-based interventions.

By evaluating these resilience assessments against observed coral recovery trajectories post-2016, this report provides critical insights into the effectiveness of such frameworks, supporting SDG Target 14.a by increasing scientific knowledge and research capacity for improved ocean health.

Methodology: A Framework for Assessing Marine Ecosystem Resilience

Study Site: Aldabra Atoll – A Case Study in Marine Protection (SDG 14.5)

Aldabra Atoll, part of the Seychelles, is a UNESCO Marine World Heritage Site and a large no-take Marine Protected Area (MPA). Its remote location and protected status make it an ideal natural laboratory for studying reef resilience in the absence of significant local anthropogenic stressors. The management of Aldabra by the Seychelles Islands Foundation (SIF) exemplifies the commitment to SDG 14.5, which aims to conserve at least 10% of coastal and marine areas. The site is subject to seasonal monsoon-driven wave energy, creating distinct environmental conditions across its coastlines.

Data Collection and Analysis: Quantifying Resilience Indicators

Data was collected at eight seaward reef sites in 2014 and 2015. The selection of resilience indicators was guided by the availability of published broadscale thresholds relevant to ecosystem function and resilience. The key indicators measured were:

• Structural Complexity: A measure of habitat availability for marine life.
• Total Fish Biomass: An indicator of overall ecosystem productivity and fishing pressure, relevant to SDG 14.4 (regulate harvesting).
• Herbivorous Fish Biomass: Critical for controlling algal growth and facilitating coral recruitment.
• Juvenile Coral Density: A direct measure of a reef’s recovery potential.
• Trophic-Level Fish Biomass: Indicates the balance and integrity of the food web.

Data from transects at 5m and 15m depths were pooled for analysis. A composite resilience index was calculated by scoring each site against the four primary thresholds (structural complexity, total fish biomass, herbivore biomass, juvenile coral density) and normalizing the sum to a scale of 0-100.

Application of Management Frameworks for SDG Alignment

To classify reefs for future management, the study employed a framework that considers both ecological condition and climate change exposure, directly addressing the adaptation needs highlighted in SDG 13.1.

1. Ecological Condition: Assessed by the pre-bleaching cover of framework-building corals (competitive and stress-tolerant species), which are essential for maintaining a net-positive carbonate budget.
2. Climate Change Exposure: Assessed using satellite-derived Degree Heating Weeks (DHW) data from 2014-2017 to quantify thermal stress.

Based on these two factors, each reef site was assigned to one of three management strategies: ‘Protect’, ‘Recover’, or ‘Transform’.

Results: Resilience Assessment of Aldabra’s Coral Reefs

Performance Against Resilience Thresholds

The overall assessment revealed high resilience across Aldabra’s seaward reefs. At the atoll level, key indicators met or exceeded the recommended scientific thresholds, demonstrating the effectiveness of its protected status in maintaining ecosystem health as envisioned by SDG 14.

• Total and Herbivorous Fish Biomass: Significantly greater than the recommended thresholds.
• Juvenile Coral Density: Significantly greater than the recommended threshold.
• Structural Complexity: Not significantly different from the threshold, with some site-level variation attributed to natural wave exposure.

The composite resilience index for the entire atoll was 87.5%. At the site level, scores ranged from 62.5% to 100%, indicating that all surveyed reefs possessed strong resilience characteristics prior to the 2016 bleaching event.

Trophic Structure and Ecosystem Health (SDG 14.4)

The trophic pyramid structure of Aldabra’s fish community was concave, with high biomass in both top predators and lower-level herbivores. This shape is characteristic of healthy, unfished reef systems and indicates that the limited, managed subsistence fishery is not compromising the ecosystem’s trophic integrity, aligning with the principles of sustainable resource management under SDG 14.4.

Management Strategy Classification and Post-Bleaching Recovery

The management assessment classified seven of the eight sites into the ‘Recover’ strategy, reflecting their high pre-bleaching coral cover (>10% framework corals) but significant exposure to thermal stress during the 2014-2017 bleaching event. One site (ARM05) was classified as ‘Transform’ due to its lower cover of framework corals. This classification provides a strategic roadmap for prioritizing management efforts to bolster climate resilience (SDG 13.1). The predicted resilience generally aligned with observed recovery trajectories, with most sites showing substantial coral cover rebound by 2022.

Discussion and Recommendations for Sustainable Management

Interpreting Resilience in the Context of SDG 14 and SDG 13

The findings strongly suggest that Aldabra’s status as a large, well-managed MPA has been crucial in fostering the high levels of resilience observed. The healthy fish populations, high juvenile coral density, and robust trophic structures are hallmarks of an ecosystem with the capacity to resist and recover from climate-related disturbances like coral bleaching. This underscores the critical role of MPAs in achieving the targets of SDG 14. However, the severe bleaching experienced in 2016 highlights that even the most resilient reefs are vulnerable, reinforcing the urgency of global efforts under SDG 13 to mitigate climate change.

Integrating Terrestrial and Marine Management (SDG 15.8)

The report identifies opportunities to further enhance reef resilience by addressing cross-ecosystem threats. A key recommendation is the eradication of invasive alien mammals (rats and cats) from Aldabra’s islands. This action directly supports SDG 15.8 (reduce the impact of invasive alien species) and is expected to have significant positive impacts on the marine environment. Restoring seabird populations would increase the natural flow of nutrient subsidies to the reefs, which has been shown to boost coral growth, recruitment, and fish biomass, thereby strengthening the entire ecosystem’s resilience to future climate shocks.

Advancing Resilience-Based Management through Partnerships (SDG 17)

This study serves as a successful example of SDG 17 (Partnerships for the Goals) and SDG 14.a (Increase scientific knowledge). It demonstrates how local management bodies like the SIF can leverage global scientific frameworks and data to generate actionable, site-specific insights. The application of broadscale thresholds proved to be a valuable, time-efficient exercise for initiating RBM in a data-limited context. For future assessments, it is recommended to:

• Develop locally-calibrated thresholds for indicators like structural complexity that are influenced by site-specific conditions (e.g., wave energy).
• Incorporate additional indicators, such as fine-scale temperature variability and nutrient inputs, to create a more comprehensive resilience profile.
• Utilize composite indices to summarize complex data for clear communication and decision-making.

Conclusion: The Path Forward for Data-Driven Reef Conservation

This report confirms that the coral reefs of Aldabra Atoll are highly resilient, a testament to its long-term protection and effective management. By applying broadscale threshold approaches, this study provides a practical model for reef managers worldwide to implement Resilience-Based Management, a critical strategy for safeguarding marine ecosystems in the era of climate change. Continuing to invest in monitoring, integrating site-specific knowledge, and addressing cross-ecosystem threats will be essential for adapting management strategies and ensuring that vital ecosystems like Aldabra continue to contribute to the global vision outlined in the Sustainable Development Goals.

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on Resilience-Based Management of coral reefs at Aldabra Atoll addresses several Sustainable Development Goals (SDGs) by focusing on marine ecosystem health, climate change impacts, and conservation management strategies.

• SDG 14: Life Below Water

  This is the most central SDG to the article. The entire study revolves around the conservation and sustainable management of a marine ecosystem—the coral reefs of Aldabra Atoll. It assesses reef health, the impacts of disturbances like coral bleaching, and the effectiveness of management within a Marine Protected Area (MPA).

• SDG 13: Climate Action

  The article directly confronts the impacts of climate change on coral reefs. It uses the 2016 global coral bleaching event, a direct consequence of rising ocean temperatures, as a case study to assess reef resilience and recovery. The management strategies discussed are framed as responses to climate-related hazards.

• SDG 15: Life on Land

  The article connects terrestrial and marine ecosystems by discussing how land-based management actions, such as the eradication of invasive alien species (rats and cats) and the restoration of seabird populations, can enhance marine ecosystem resilience through nutrient subsidies. This highlights the importance of integrated ecosystem management.

2. What specific targets under those SDGs can be identified based on the article’s content?

The article’s content aligns with several specific targets under the identified SDGs.

1. SDG 14: Life Below Water

   • Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.

     The article mentions local stressors that can impact coral reefs, including “plastic pollution.” It notes that “An estimated 500 tonnes of plastic pollution have accumulated along Aldabra’s coastline,” and that the managing body (SIF) “undertakes active management of this issue through regular clean-ups.” It also discusses the influence of nutrient inputs from seabird guano, linking it to reef resilience.

   • Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans.

     This is the core theme of the article. The study is an application of “Resilience-Based Management (RBM)” which “aims to maintain ecosystem function and maximise resilience.” The entire methodology, including the assessment of resilience indicators and the classification of reefs into management strategies (‘protect’, ‘recover’, ‘transform’), is designed to inform actions for protecting and restoring the Aldabra reef ecosystem.

   • Target 14.4: By 2020, effectively regulate harvesting and end overfishing, illegal, unreported and unregulated fishing and destructive fishing practices and implement science-based management plans…

     The article assesses the impact of a “small-scale subsistence fishery” by comparing fish biomass against thresholds for unfished areas. It notes that “even within the most heavily fished area, biomass ranged from 986 to 4267 kg/ha,” suggesting that “current levels of subsistence fishing are having limited impacts.” It also mentions the establishment of “six designated fishing zones to monitor and manage fishing pressure.”

   • Target 14.5: By 2020, conserve at least 10 per cent of coastal and marine areas, consistent with national and international law and based on the best available scientific information.

     The study is set in “Aldabra, a UNESCO Marine World Heritage Site,” which is a “remote MPA” and a “Special Reserve.” The article explicitly mentions the “maintenance of the no-take protected area (2559 km² since 2018; formerly 439 km²),” demonstrating a direct contribution to this target.

   • Target 14.a: Increase scientific knowledge, develop research capacity and transfer marine technology…

     The study itself is an example of this target in action. It applies advanced ecological assessment frameworks (“broadscale threshold approaches”) to a local context, generating scientific knowledge to guide management. The discussion highlights the need for more data and suggests that “applying similar resilience-based assessments across Seychelles and other island groups” would strengthen management, promoting the development of research capacity.

2. SDG 13: Climate Action

   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.

     The article is fundamentally about strengthening the resilience of coral reefs to climate-related hazards. It evaluates “reef resilience… towards large scale climatic disturbances” like the “2016 bleaching event” caused by thermal stress. The development of a “composite resilience index” and management strategies are direct efforts to build adaptive capacity.

   • Target 13.3: Improve education, awareness-raising and human and institutional capacity on climate change mitigation, adaptation, impact reduction and early warning.

     By publishing this research and providing a framework for “Resilience-Based Management (RBM),” the study contributes to the institutional capacity of organizations like the Seychelles Islands Foundation (SIF). It provides a “transparent, structured rationale for selecting indicators” and offers a model for other reef managers, thereby improving capacity for climate change adaptation in marine conservation.

3. SDG 15: Life on Land

   • Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species.

     The article mentions management efforts on the atoll that include “native species re-introductions,” which directly relates to halting biodiversity loss and protecting threatened species within the terrestrial part of the World Heritage Site.

   • Target 15.8: By 2020, introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species.

     The study explicitly discusses the role of invasive species. It mentions “invasive alien species eradications” as part of ongoing management. It further proposes that “eradicating introduced rats and cats from Aldabra” is of the “highest priority” to restore seabird populations, which in turn would enhance the resilience of the adjacent marine ecosystems.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article is rich with specific, quantifiable indicators used to assess reef resilience and ecosystem health, which can directly serve as metrics for tracking progress towards the SDG targets.

1. Indicators for SDG 14 (Life Below Water)

   • Structural Complexity: Measured on a 6-point scale and compared to a threshold. This indicates the physical habitat structure available for marine life, relevant to Target 14.2.
   • Total Fish Biomass: Measured in kg/ha and compared to a threshold of 1000 kg/ha. This is used to assess fishing pressure and overall ecosystem health, relevant to Targets 14.2 and 14.4.
   • Herbivore Biomass: Measured in kg/ha and compared to a threshold of 177 kg/ha. This indicates the reef’s capacity to control algae and facilitate coral recovery, relevant to Target 14.2.
   • Juvenile Coral Density: Measured as colonies per m² and compared to a threshold of 6.2 juveniles/m². This is a direct measure of a reef’s recovery potential, relevant to Target 14.2.
   • Trophic Pyramid Structure: The relative biomass distribution among five trophic levels is compared to models for “fished” and “unfished” seascapes. This provides insight into ecosystem integrity and fishing impacts (Target 14.4).
   • Live Coral Cover (%): Measured before (2014) and after (2016, 2022) the bleaching event to assess impact and recovery rates. This is a key indicator of ecosystem health (Target 14.2).
   • Framework Coral Cover (%): The percentage of competitive and stress-tolerant corals is compared to a 10% threshold to determine the reef’s carbonate budget potential and classify it for management (Target 14.2).
   • Marine Debris Levels: The article quantifies plastic pollution (“An estimated 500 tonnes”) and mentions clean-up efforts, serving as an indicator for Target 14.1.
   • Proportion of Marine Area Protected: The size of the no-take MPA (2559 km²) is a direct indicator for Target 14.5.

2. Indicators for SDG 13 (Climate Action)

   • Degree Heating Weeks (DHW): Used to quantify thermal stress exposure. The article uses a threshold of >4 °C-weeks to classify reefs for management strategies based on their climate vulnerability (Target 13.1).
   • Composite Resilience Index: A score synthesized from multiple indicators (fish biomass, juvenile corals, etc.) to provide an overall measure of a reef’s ability to withstand climate shocks (Target 13.1).
   • Post-Bleaching Recovery Trajectory: Measured as the percentage of pre-bleaching coral cover regained over time (by 2022). This is a direct measure of adaptive capacity (Target 13.1).

3. Indicators for SDG 15 (Life on Land)

   • Status of Invasive Alien Species: The article mentions ongoing “invasive alien species eradications” and proposes the eradication of rats and cats as a priority. The presence/absence or population density of these species is an indicator for Target 15.8.
   • Seabird-derived Nutrient Levels: The article mentions isotopic analysis of algae to detect nutrient inputs from seabirds, which is an indicator of the health of the land-sea ecosystem link, relevant to the goals of Target 15.8.

4. Table of SDGs, Targets, and Indicators

SDGs	Targets	Indicators Identified in the Article
SDG 13: Climate Action	13.1: Strengthen resilience and adaptive capacity to climate-related hazards. 13.3: Improve institutional capacity on climate change adaptation.	Degree Heating Weeks (DHW) as a measure of thermal stress. Composite resilience index score (%). Post-bleaching coral cover recovery trajectory (%). Application of Resilience-Based Management (RBM) frameworks.
SDG 14: Life Below Water	14.1: Reduce marine pollution and debris. 14.2: Sustainably manage and protect marine ecosystems and strengthen their resilience. 14.4: Regulate harvesting and end overfishing. 14.5: Conserve coastal and marine areas. 14.a: Increase scientific knowledge and research capacity.	Quantity of accumulated plastic pollution (tonnes). Total fish biomass (kg/ha). Herbivorous fish biomass (kg/ha). Juvenile coral density (colonies/m²). Structural complexity score. Live coral cover (%). Framework coral cover (%). Trophic pyramid structure (relative biomass distribution). Area of Marine Protected Area (km²). Number and application of scientific assessment studies.
SDG 15: Life on Land	15.5: Reduce degradation of natural habitats and halt biodiversity loss. 15.8: Prevent and reduce the impact of invasive alien species.	Status of invasive alien species (presence/eradication efforts for rats and cats). Status of native species re-introductions. Levels of seabird-derived nutrient subsidies in adjacent marine ecosystems.

Source: nature.com