By Moramade White
Executive summary
Coral reefs are vital marine ecosystems. Although they cover less than 1 per cent of the ocean's surface, they are home to about 25 per cent of global marine biodiversity and provide essential ecosystem services for millions of people. In Haiti, these reefs play a crucial role for food security, coastal protection and the local economy of coastal communities.
Today, these fragile ecosystems are under multiple and growing pressures: ocean warming, acidification, coastal pollution, deforestation-related sedimentation, destructive fishing practices and lack of integrated management. Faced with this accumulation of stress, understanding the resilience of coral reefs becomes a scientific and societal priority.
This doctoral research aims to assess the resilience of the coral reefs of Haiti by analysing the growth of massive corals over several decades. By mobilizing sclerochronology and densitometry approaches, the study reconstructs the history of environmental and climatic stress, identifies the phases of resistance and recovery, and quantifys the adaptive capacity of corals in response to disturbances. The expected results will provide decision support tools to guide strategies for the conservation, restoration and sustainable management of Haitian reefs in a context of global change.
Keywords: Coral reefs, Resilience, Sclerochronology, Haiti, Climate change
Introduction
Coral reefs: essential but threatened ecosystems
Coral reefs are among the richest and most productive ecosystems on the planet. Although covering less than 1% of the ocean's surface, they are home to nearly 25% of known marine biodiversity (Moberg & Folke, 1999; Spalding et al., 2001). They are also a fundamental pillar for human societies, especially in tropical regions, by protecting the coasts from erosion and storms, providing essential fisheries resources, generating tourism revenues and bringing significant cultural value (Jackson et al. 2014).
However, these exceptional ecosystems are also among the most threatened in the world. For several decades, coral reefs have been subject to an accumulation of pressures related to human activities and global climate change. Warming surface waters, increasing the frequency and intensity of marine heat waves, coastal pollution, soil inputs, increased turbidity and overfishing weaken their ecological functioning and threaten their future (Hughes et al., 2017; Hoegh-Guldberg et al., 2018).
Globally, episodes of massive bleaching since the late 1990s illustrate the magnitude of the ongoing ecological crisis. The first global bleaching event in 1997-1998 marked a historic turning point, revealing the extreme vulnerability of corals to rising water temperatures. Since then, these events have multiplied and intensified in all tropical regions (Wilkinson, 2000; Jackson et al., 2014; Hughes et al., 2018).
Caribbean region: a highly impacted area
The Caribbean region has not been spared by this global dynamic of degradation. The bleaching events of 2005 and 2010 resulted in considerable loss of living corals. In some areas, more than 50 per cent of settlements have disappeared, particularly in the United States Virgin Islands, while other countries such as Barbados or the Dominican Republic have recorded significant mortality (Wilkinson & Souter, 2007; Jackson et al., 2014; Eakin et al., 2010).
These losses are not only the result of global warming. They are the result of a combination of global stress, such as rising ocean temperatures and climatic anomalies, and local pressures such as pollution, sedimentation, habitat degradation and overexploitation of marine resources. This interaction between global and local factors weakens the ability of reefs to withstand disturbance and recover after stress episodes (Burke et al., 2011; Hughes et al., 2017; McClanahan et al., 2019).
The coral reefs of Haiti: a critical case still poorly known
The situation in Haiti is of particular concern. Coral reefs are subject to rapid surface water warming, but also to intense coastal pressures: domestic and industrial pollution, earth inputs from massive deforestation, high turbidity, destructive fishing practices and lack of integrated coastal zone management.
Despite this apparent vulnerability, scientific knowledge about Haitian reefs remains limited. The tolerance thresholds of local corals, their sensitivity to climatic and environmental stresses, as well as their real capacity for resistance and recovery, are still unknown. This scientific gap is a major obstacle to effective conservation and sustainable management strategies.
It is in this context that this doctoral research, which aims to better understand the resilience of the coral reefs of Haiti through the study of massive corals, true natural archives of the climate and the environment.
Theoretical and methodological framework
Massive corals: high-resolution natural archives
Massive corals, such as Diplomaria, Orbicella or Siderastrea, build their limestone skeleton in successive annual layers, in the manner of tree growth rings. Each year, they record in their skeleton valuable information on the environmental conditions they have passed through: water temperature, nutrient availability, turbidity, thermal stress or extreme episodes.
Using techniques such as sclerochronology (study of annual growth bands) and densitometry (measurement of skeletal density), it is possible to reconstruct the history of coral growth over several decades or even centuries. These natural archives offer a unique and time-sensitive vision of coral response to environmental and climate change.
The concept of resilience: a multidimensional approach
The resilience of a coral reef is not limited to its ability to survive one-off stress. It is based on several complementary dimensions that provide insight into coral response dynamics to disturbance (Elmqvist et al. 2003):
- Sensitivity : describes the initial reaction of coral to an environmental disturbance.
- Resistance : corresponds to the coral's ability to maintain its physiological performance despite the stress.
- Recovery : measures the coral's ability to regain its initial performance after disturbance.
- Resilience : integrates both resistance and recovery, providing a global vision of adaptive capacity.
In this research, these concepts are quantified from three key parameters of coral growth: linear extension (length growth), skeletal density and calcification (extension and density combination).
Integrated methodology
To analyse the resilience of Haiti's massive corals, this study takes an integrated approach combining: - A spatial review at different geographical scales;
- Analysis of the main climatic indices (ENSO, NAO, AMO and sea surface temperature anomalies);
- Sclerochronology and densitometry techniques to quantify coral extension, density and calcification;
- Crossing these data with local environmental variables such as turbidity, underwater visibility and cloudiness.
The resulting time series identify the stress, resistance and recovery phases, as well as the short- and long-term coral growth dynamics.
Quantification of resilience
Resistance: Ability to maintain performance during stress
Resistance describes the ability of a coral to maintain its physiological functions in the face of a disturbance without collapse. In concrete terms, it indicates whether coral manages to maintain its growth (in length, density or calcification) for a difficult period, for example during an abnormal warming of water or cyclone. Conversely, a weak coral will quickly see its performance fall from the first disturbances.
Resistance is therefore a key indicator of the immediate vulnerability of corals to environmental and climatic stress.
Recovery: ability to recover initial performance
Recovery corresponds to the coral's ability to return to normal performance after the end of stress. Coral may have been heavily affected during a difficult period, but then show a remarkable ability to recover. This phase can be compared to recovery after a disease: some organisms take a long time to recover, others recover quickly and regain their vitality.
In corals, good recovery results in a resumption of growth, skeletal density and calcification, indicating that the organism has overcome the stress episode.
Resilience: a balance between resistance and recovery
The resilience of a growth parameter (extension, density or calcification) combines these two essential dimensions: the ability to resist and the ability to recover. A truly resilient coral is not necessarily the one that never experiences stress, but the one that manages to pass through the disturbances without irreversible damage and then rebuild.
Global resilience: an integrated vision of coral health
The overall resilience of coral incorporates all its growth performance: the speed at which it grows (extension), the strength of its skeleton (density) and its ability to produce calcium carbonate (calcification). This comprehensive approach provides a synthetic reading of coral health and its ability to cope with climate and environmental change.
A coral with a strong global resilience is a coral that is more resistant to stress, recovers more quickly and helps to maintain the structure and functions of the reef.
Importance of resilience indices for Haiti
In the Haitian context, where reefs are subject to both global climatic pressures and intense local impacts, these indices are real tools to help decision-making. They identify:
- The most robust reefs to protect as a priority;
- Those requiring ecological restoration actions;
- Areas where the reduction of anthropogenic pressures is most urgent.
Quantifying the resilience of Haitian corals thus allows to better understand their biological limits, but also to reveal their potential for survival in the face of the climate challenges of the 21st century. These indices also compare temporal performance of corals and between different reef areas, and identify the most resilient colonies or reefs.
Implications for sustainable management
The expected results of this research go far beyond scientific understanding. They provide concrete tools to: - Identify the reefs or species most resistant to environmental stress;
- Detect critical vulnerability thresholds;
- Orient restoration and conservation actions;
- Support the implementation of sustainable management strategies tailored to the Haitian context.
In a country where reefs play a fundamental role in food security, coastal protection and the livelihoods of coastal communities, understanding coral resilience is an essential step in anticipating the impacts of climate change and enhancing the adaptation of coastal socio-ecosystems.
Conclusion
In the face of climate change and growing local pressure, Haiti's coral reefs are at a critical juncture. This research will help fill an important scientific gap by providing a thorough understanding of the mechanisms of sensitivity, resistance, recovery and resilience of massive corals.
By revealing how Haitian corals respond to environmental and climate stress, it paves the way for more focused management actions, based on rigorous scientific data, and adapted to local realities. To preserve the resilience of the reefs is also to preserve the future of the coastal communities and the exceptional natural wealth of Haiti.
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White Moramade, Doctoral
Climate Change Research Team (CRT2)
Quisqueya University
blamo82@yahoo.fr
