Original article by:
Jay R.S. Doorga, Université des Mascareignes
Olivier Pasnin, Reef Conservation
Yeshna Dindoyal, Climate Change Lawyer, Independent
Clara Diaz, School of Biological and Marine Science, University of Plymouth
Tropical coral reefs, such as the ones found in Mauritius, are vital for biodiversity and coastal protection. They are particularly vulnerable to warming ocean temperatures and face a combination of climate change and local pressures. To adequately protect what has been called the rainforest of the ocean, we need to assess coral reef climate vulnerabilities and the impact of local stressors such as agricultural pollution and coastal development projects.
The reefs surrounding Mauritius are experiencing rising sea surface temperatures at a rate of 0.16°C per decade, surpassing the global average of 0.11°C. This warming, combined with frequent overshoot of the bleaching threshold, has led to severe declines in coral cover. Between 2004 and 2019, hard coral declined by 40% and soft coral by 83%, with algae increasing by 78%.
These pressures are exacerbated by local stressors, including industrial and urban sewage outflows, agricultural runoff, coastal development, and outbreaks of coral-eating crown-of-thorns starfish (COTs). While these stressors are known, there is a need to map the impact of these climatic and human driven stressors to allow effective monitoring and intervention.
Understanding Coral Reef Vulnerabilities
The study employed a Multi-Criteria Decision-Making (MCDM) model and Geographic Information Systems (GIS) to analyse coral reef vulnerabilities under six scenarios, focusing on 10 climate, ecological, and socio-economic stressors as listed in table 1.
Table 1: Evaluation criteria for coral vulnerability in oceanic islands
Climate-Oriented Scenarios:
The study revealed that temperature changes play a key role in determining vulnerability along Mauritius’ coasts—areas in the southeast face high to critical risks due to significant temperature fluctuations. Meanwhile, the east and southeast of the island are particularly vulnerable to mean and maximum sea surface temperatures. In the eastern region, average temperatures often exceed 27.5°C, a critical point that triggers coral bleaching.
Ecological Scenarios:
Scenarios emphasising coral predator outbreaks highlighted severe impacts in the southeast and northwest, indicating that COTs outbreaks amplify climate-related stressors.
Socio-Economic Scenarios:
Agricultural pollution and hotel construction were found to uniformly exacerbate coral vulnerabilities along the eastern and western coasts. The southeast remains a critical hotspot due to agricultural runoff and sedimentation from tourism infrastructure.
Aggregated Vulnerability Scenarios
By combining all scenarios, the study generated an aggregated vulnerability map. As seen in figure 6 below, the southeast and eastern coasts are the most critical zones for coral vulnerability, with moderate to high impacts in the north and west.
The model’s findings closely align with real-world observations, such as bleaching surveys and local expertise observations. Diving surveys in high-risk areas such as Belle Mare revealed predominantly bleached coral colonies, confirming the model’s accuracy.
Also, a comparison of sea surface temperature trends over two decades shows a rise of 0.66°C between 1985–2003 and 2003–2020. The increase in sea surface temperature over the 2003 to 2020 period is reported at 0.16 °C per decade which is higher than the global average of 0.11 °C per decade. The frequency of temperatures exceeding the bleaching threshold has increased, weakening coral resilience and amplifying future risks.
The Path Forward: Resilience and Protection
There is an urgent need for effective management strategies that should focus on building resilience, including:
- Expanding and making Marine Protected Areas (MPAs) more effective: Strategically designed and strictly enforced Marine Protected Areas (MPAs) should focus on building resilience to climate change, addressing local stressors through integrated coastal management, and safeguarding the well-being of local communities.
- Targeting Local Stressors: Policies must mitigate fertiliser use and agricultural runoff, regulate coastal development, and control reef predator outbreaks to reduce cumulative impacts.
- Harnessing Technology: Satellite-based monitoring offers a cost-effective approach to tracking stressors and coral health, enabling timely interventions.
Mauritius exemplifies the vulnerabilities of island ecosystems, where climate and human pressures intersect. Its reefs are not only vital for biodiversity but also for the economy, supporting fisheries and tourism while protecting coastlines.
This study provides a blueprint for preserving coral reefs in Mauritius and beyond. By leveraging scientific research and community-focused policies, we can build resilience in the face of intensifying challenges, ensuring these ecosystems thrive for generations to come.
KEY FINDINGS
Importance and Vulnerabilities of Coral Reefs
- Tropical coral reefs, including those in Mauritius, are critical for biodiversity and coastal protection but are highly susceptible to climate change and local pressures.
- Rising sea surface temperatures (SSTs) and frequent exceedances of bleaching thresholds are causing severe declines in coral cover.
Temperature and Coral Bleaching
- Sea surface temperatures around Mauritius are increasing at 0.16°C per decade, above the global average of 0.11°C.
- Between 2004 and 2019, hard coral cover declined by 40%, soft coral by 83%, and algae increased by 78%.
- The southeast and eastern coasts face the highest risks due to significant temperature fluctuations and exceedances of critical bleaching thresholds (27.5°C).
Local Stressors
- Local pressures, including agricultural runoff, coastal development, sewage outflows, and crown-of-thorns starfish (COTs) outbreaks, exacerbate climate impacts.
- Agricultural pollution and tourism-related sedimentation critically impact coral reefs in the southeast and eastern regions.
OTHER RESEARCH BY THE AUTHORS:
Surging seas, rising sea levels, and sinking communities: The urgent need for climate adaptation in small island states. Link:https://www.sciencedirect.com/science/article/pii/S1462901124001229
Assessment and management of coastal erosion: Insights from two tropical sandy shores in Mauritius Island. Link:https://www.sciencedirect.com/science/article/pii/S0964569121003069
GIS-based multi-criteria modelling of flood risk susceptibility in Port Louis, Mauritius: Towards resilient flood management. Link:https://www.sciencedirect.com/science/article/pii/S2212420921006440
Original Paper Risk assessment of coral reef vulnerability to climate change and stressors in tropical islands: The case of Mauritius – ScienceDirect
Main photo from Jay Doorga.
Charles Telfair Centre is an independent nonpartisan not for profit organisation and does not take specific positions. All views, positions, and conclusions expressed in our publications are solely those of the author(s).