Protection of coral reef fish delivers ecosystem-critical biocontrol of coral-eating starfish across the Great Barrier Reef – Nature

Report on Biocontrol Strategies for the Great Barrier Reef and Alignment with Sustainable Development Goals (SDGs)

Introduction: Addressing SDG 14 (Life Below Water)

This report evaluates the efficacy of biological control (biocontrol) measures in managing Crown-of-thorns starfish (CoTS, Acanthaster ssp.) populations on the Great Barrier Reef (GBR). CoTS represent a significant threat to the GBR, a critical marine ecosystem whose protection is central to achieving Sustainable Development Goal 14 (Life Below Water). By analyzing the role of predatory reef fish in moderating CoTS outbreaks, this study assesses how conservation strategies such as marine reserves and fisheries regulations contribute to SDG Target 14.2, which calls for the sustainable management and protection of marine and coastal ecosystems to enhance their resilience. A meta-community model of the GBR was utilized to demonstrate the impact of these interventions on ecosystem health and stability.

Analysis of Management Interventions and Ecosystem Resilience

The Critical Role of Historical Conservation Efforts (SDG 14.2, 14.4, 14.5)

Model simulations confirm that management strategies implemented in the Great Barrier Reef Marine Park, particularly the major re-zoning and fisheries regulations of 2004, have been instrumental in safeguarding the ecosystem. These interventions have delivered significant benefits that directly support multiple targets within SDG 14.

• Restoration of Fish Stocks (SDG 14.4): The regulations, including no-take zones and catch limits, effectively regulated harvesting and reversed the decline of predatory fish populations, such as groupers and emperors. This aligns with the goal to end overfishing and restore fish stocks.
• Conservation of Marine Areas (SDG 14.5): The establishment of no-take marine reserves has proven to be a successful method for conserving critical marine areas, leading to lower CoTS densities and reduced outbreak frequencies within these protected zones.
• Strengthening Ecosystem Resilience (SDG 14.2): By protecting natural predators of CoTS, these conservation measures have enhanced the GBR’s natural biocontrol capacity, mitigating coral loss and strengthening the overall resilience of the reef ecosystem against pest outbreaks.

The Counterfactual Scenario: Averting an Ecological Tipping Point

To quantify the importance of these historical interventions, the model simulated a counterfactual scenario in which no management regulations were ever implemented. The results indicate that these policies were critical in preventing a catastrophic ecosystem regime shift. Without them, the GBR would have likely experienced:

1. A consistent and severe decline in predatory fish populations, leading to their functional extinction by approximately 2025.
2. A subsequent meso-predator release, resulting in a new ecological state characterized by continuous and widespread CoTS outbreaks.
3. Substantially lower coral cover and a critical loss of ecosystem resilience, undermining the objectives of SDG 14.

These findings provide a strong evidence base that science-based management plans have successfully averted a major tipping point, preserving the ecological integrity of the GBR.

Future Projections and Management Efficacy towards 2050

Evaluating Future Biocontrol and Management Strategies

The report modeled several potential future management scenarios to assess their efficacy in further protecting the GBR. The projections highlight the complexities of enhancing ecosystem resilience in the face of multiple stressors.

• Fisheries and Zoning Management: While further expanding protected zones or reducing catch limits leads to increased predatory fish stocks, the corresponding gains in coral cover are not substantial. This is because external drivers, particularly climate change, tend to overwhelm the benefits of these localized actions. Furthermore, expanding protected zones without reducing the total allowable catch can displace fishing effort, creating new pressure points in unprotected areas.
• Manual CoTS Control: Over the next decade (to 2040), direct manual control of CoTS is projected to be the most reliable strategy for reducing the number of reefs experiencing outbreaks and increasing coral cover. This intervention provides a tangible, short-term action to support the goals of SDG 14.2.

The Overarching Threat of Climate Change (SDG 13: Climate Action)

A critical finding of this report is the limitation of local management actions under future climate projections. Model scenarios demonstrate that beyond 2040, the escalating impacts of climate change, such as marine heatwaves causing coral bleaching, will severely limit the effectiveness of interventions based on biocontrol and manual culling. The underlying resilience of CoTS populations, combined with climate-driven coral mortality, will overwhelm the benefits of these strategies. This underscores that local conservation efforts, while essential, are insufficient on their own. Achieving SDG 14 for the GBR and global coral reefs is fundamentally dependent on urgent and effective global implementation of SDG 13 (Climate Action) to mitigate global warming.

Conclusion and Implications for Sustainable Development

Key Takeaways for Marine Governance

This analysis provides clear directives for the ongoing sustainable management of the GBR and other marine ecosystems.

• Historical fisheries management and the establishment of marine reserves have been demonstrably successful in contributing to SDG 14 by protecting predatory fish, limiting CoTS outbreaks, and averting a detrimental regime shift on the GBR.
• While maintaining these protections is critical, further expansion of these specific approaches is projected to yield diminishing returns for coral health, particularly as climate change impacts intensify.
• A combined approach of continued conservation biocontrol, supported by targeted manual CoTS removal, offers the most effective strategy for enhancing reef resilience in the short to medium term.
• The long-term health and survival of the Great Barrier Reef are inextricably linked to global success in achieving SDG 13. Without significant global action to combat climate change, local management efforts will ultimately be overwhelmed.

Analysis of Sustainable Development Goals in the Article

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

The article addresses several interconnected Sustainable Development Goals (SDGs) by focusing on the management of the Great Barrier Reef (GBR), a critical marine ecosystem. The primary SDGs identified are:

• SDG 14: Life Below Water: This is the most central SDG to the article. The text is entirely focused on conserving and sustainably using the marine resources of the GBR. It discusses the health of coral reefs, the management of fish stocks, the impact of pest species on marine biodiversity, and the role of marine protected areas. The article’s core argument revolves around protecting marine ecosystems from collapse.
• SDG 13: Climate Action: The article explicitly identifies climate change as a major, escalating threat to the GBR. It states that “beyond 2040, the escalating impacts of climate change… will limit the effectiveness of interventions.” It also mentions “marine heatwaves” as a key environmental stressor. The management actions discussed, such as controlling Crown-of-thorns starfish (CoTS) outbreaks, are presented as measures to strengthen the ecosystem’s resilience against these climate-related impacts.
• SDG 15: Life on Land: While seemingly focused on terrestrial ecosystems, this goal includes a target directly relevant to the article’s subject. The article consistently refers to CoTS as a “pest species” causing widespread damage, analogous to an invasive species. The entire study evaluates methods to manage and control this pest species to protect biodiversity (corals) and ecosystem function.

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

Based on the issues discussed, the following specific SDG targets are relevant:

1. Under SDG 14 (Life Below Water):
   • 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…” The article directly addresses this by demonstrating how fisheries management and marine reserves have helped in “maintaining the resilience of the GBR ecosystem” and preventing a “major tipping point” characterized by low coral cover. The goal of the interventions is to mitigate coral loss and protect the reef ecosystem.
   • Target 14.4: “By 2020, effectively regulate harvesting and end overfishing… and implement science-based management plans…” The article’s central thesis is that “marine reserves and other fisheries regulations” have been critical. It details how regulations such as “protected zones where fishing is not permitted, catch and size limits, seasonal closures and gear restrictions” have helped recover populations of predatory fish, thereby preventing overfishing of these key species.
   • Target 14.5: “By 2020, conserve at least 10 per cent of coastal and marine areas…” The article highlights the importance of protected areas, noting that “CoTS densities and outbreak frequencies have since been found to be consistently lower in GBR protected zones.” It also evaluates scenarios for “Increasing the fraction of protected reefs from 30% to 40%… or 60%.”
2. Under SDG 13 (Climate Action):
   • Target 13.1: “Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.” The article frames local management actions as a way to bolster the GBR’s resilience against global climate threats. It notes that CoTS impacts are “compounded by the destructive effects of escalating climate change.” By controlling CoTS, managers can mitigate one major stressor, thereby strengthening the reef’s ability to withstand and recover from climate-related events like marine heatwaves.
3. Under SDG 15 (Life on Land):
   • 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.” Although CoTS are native, their outbreak dynamics are treated as a pest problem. The article is dedicated to evaluating measures to control this “pest species,” including “manual removal of starfish,” “intensive culling,” and “conservation biocontrol” (protecting natural predators) to reduce their devastating impact on the coral reef ecosystem.

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

The article mentions or implies several quantitative and qualitative indicators that can be used to measure progress towards the identified targets:

• Percentage Coral Cover: This is a primary indicator of ecosystem health and resilience (Targets 14.2, 13.1). The study’s model projections consistently use “percentage coral cover” as a key output variable to measure the success or failure of different management scenarios.
• Abundance of Predatory Fish: This serves as an indicator for the effectiveness of fisheries management (Target 14.4). The article specifically measures and models the “number of mature groupers per hectare” and “number of mature emperors per hectare” to show how their populations respond to regulations.
• Frequency and Extent of CoTS Outbreaks: This is a direct indicator of the success of pest control measures (Target 15.8). The model tracks the “percentage of reefs with CoTS outbreaks” as a critical measure of the problem’s scale and the efficacy of biocontrol and manual culling.
• Proportion of Marine Area Protected: This indicator measures progress towards conservation goals (Target 14.5). The article explicitly mentions the current protected area (“30%”) and models the potential benefits of increasing this proportion, thus using it as a key management lever and indicator.
• Implementation of Management Plans: The article implicitly uses the existence and enforcement of various management strategies as an indicator of progress (Target 14.4). These include “zoning,” “fisheries management strategies,” “catch and size limits,” and the “multi-million-dollar CoTS control programme.”

4. Table of SDGs, Targets, and Indicators

Source: nature.com