Adaptation strategies for coral reef ecosystems in Small Island Developing States: Integrated modelling of local pressures and long-term climate changes

https://doi.org/10.1016/j.jclepro.2019.119864Get rights and content

Highlights

  • Using an integrative approach rises the chance of successful execution of adaptation plans.

  • Planning for reefs requires integrated modelling of local pressures and long-term climate changes.

  • Bayesian Network was used to integrate multidisciplinary assessments with experts’ opinion.

  • The reefs’ resilience would be threatened severely by 2070 in the absence of adaptation strategies.

Abstract

Planning and decision-making vastly benefit from a holistic and systematic understanding of the long-term impacts of climate change and other non-climatic stressors on the health and resilience of coral reef ecosystems, and the efficacy of adaptation strategies and management interventions on mitigating these impacts and maintaining ecosystem condition and associated ecosystem service. This study reports on an approach to modelling coral reef stressors and possible adaptation interventions using the coral reef ecosystem of Port Resolution on Tanna Island, Vanuatu as the case study serving as a microcosm of endangered Pacific Small Island Developing States (SIDS). A novel participatory modelling framework was developed and followed in a stepwise manner to integrate local and long-term climate change pressures by coupling structural analysis and the Bayesian Network (BN) techniques. The BN model was quantified through an advanced consolidated data-induced, evidence-based, and expert-driven approach that incorporated: (1) projections of future climate conditions and changing human activities; (2) the influences of multiple stressors including physical environmental and sociological factors; and (3) spatial variability in the key processes and variables. The first and second phases conceptualised the whole system by providing a graphical presentation of system variables within the Driver-Pressure-State-Impact (DPSI) framework using the structural analysis technique. In the third phase, the BN technique was used to integrate the outcomes of multidisciplinary assessments and analysis with experts’ opinion. The BN modelling phase was completed based on evidence extracted from literature which reported the results of regional and downscaled climate models, GIS-based analysis, parametrised data obtained from the region, and tacit knowledge elicited from experts. The validated model was employed to anticipate the future health and resilience condition of coral reefs under different sets of climatic trajectories and adaptive responses scenarios. The results predict the risks to the health and resilience of the Port Resolution coral reef system from the adverse impacts of climate change and harmful human activities and the possible success of adaptations strategies. A sobering conclusion was that despite the current satisfactory condition of coral reefs in the case study zone, their health and resilience would be severely threatened by 2070 in the absence of implementing adaptation strategies and associated sustainable management interventions.

Introduction

Global population growth and increasing human impacts on ecosystems raise questions around the functionality and capability of marine ecosystems to provide adequate services which support social wellbeing to an acceptable level (Santos-Martín et al., 2013). Variations in the functioning and composition of marine ecosystems and the resultant threats and opportunities of ecosystem changes can significantly affect human well-being (IPCC, 2014). According to the Millennium Ecosystem Assessment (MEA, 2005), in many instances, the flow of ecosystem services is being impaired as a direct result of changing climate conditions as well as non-climatic pressure. Within several decades, this current trend will result in the alteration of all ecosystems and may have severe negative impacts on ecosystem services and human well-being (Colls et al., 2009). Therefore, it is of paramount importance to identify, assess, and understand the provision of ecosystem services, to put more planning efforts toward improving the health and resilience of the supporting ecosystems. However, recommending management strategies or adaptation planning should incorporate the uncertainties in future social and natural land conditions under different climate change pathways (Comte and Pendleton, 2018).

Small Island Developing States (SIDS) are among the most vulnerable communities, being highly dependent on services from coastal ecosystems. SIDS are a group of 57 small island countries listed by the United Nations Department of Economic and Social Affairs (UNDESA) (Spector et al., 1994) that share similar sustainable development challenges despite specific cultural and geographical differences (Hay, 2013). A range of factors, namely, remoteness, limited public education services and community awareness, being highly exposed to natural extreme events and disasters, and limited accessible funds are considered the most important challenges for SIDS. Inopportunely, coral reefs are also particularly vulnerable to multiple local-based activities and pollution, and climatic distresses (Hughes et al., 2017; Ateweberhan et al., 2013). Globally, coral reefs provide services and livelihoods for millions of people (Hughes et al., 2017). For SIDS in particular, coral reefs are among key ecosystems for sustaining livelihoods (Martin et al., 2017) and, together with mangroves, important for coastal protection against extreme weather events (Hughes et al., 2017). Thus, planning for SIDS communities under rapidly changing and uncertain non-climatic and climatic conditions requires a realistic and long-term evaluation of impacting factors and potential management interventions for minimising the risks to these ecosystem services and that are effective and appropriate (Betzold, 2015; Robinson, 2017). Tanna Island, Vanuatu, was selected as a case study region since it represents a typical microcosm of Pacific-SIDS geography and human settlements that are highly reliant on ecosystem services. It is to be noted that this study was undertaken as a part of an extensive project titled “EcoAapt in the Pacific” that aimed to identify appropriate adaptation interventions in the coastal zones of Pacific island states and territories in the face of rapidly changing climate and ongoing capital-intensive developments.

However, assessments of erratic, multidimensional and complex systems, such as coral reef ecosystems (Harvey et al., 2018) that exhibit a high level of uncertainty (Hoegh-Guldberg et al., 2019), mandates the employment of an integrated approach (Hafezi et al., 2018). Moreover, each assessment requires a customised procedure that can cater to the specific needs and characteristics of each system (Voinov and Shugart, 2013). Particularly, environmental systems, which are under constant changing climate conditions, are more likely to yield reliable outcomes when an integrated modelling approach is exploited (Hafezi et al., 2018). Besides, assessments of the socio-economic components of the coral reefs’ health and resilience system, as well as region-specific characteristics, opportunities, and limitations mandate the elicitation of local stakeholders’ knowledge in conjunction with other inputs, in order to derive reliable equations and probability distributions (Hoegh-Guldberg et al., 2019). Accordingly, this study required a modelling approach that is capable of taking into account the following aspects: 1) multiple factors that are conventionally dealt with by different disciplines but that account for a wide range of climate change-induced risks, and an assessment of the central ecosystem; 2) integrative evaluations that combine both quantitative and qualitative types of data; 3) understanding of the causal relationship between the multiple stressors and reef health and resilience; and 4) effective treatment of the modelling complexities and uncertainties associated with the array of social and environmental factors. In other words, adoption of an advanced and practical approach and strategy was a mandate rather than an option to incorporate different types of qualitative and quantitative multidisciplinary data as well as to include a proper description and quantification of uncertainty in the modelling and assessment processes. For this purpose, an innovative participatory and integrated modelling strategy was to be developed that is highly efficient in integrating local and long-term climate change pressures under the specific characteristics of SIDS.

Recently, the Bayesian Network (BN) technique has gained researchers attention (Kerebel et al., 2019) and been employed as the main modelling platform in different environmental studies such as ecosystems and ecological assessments (Smith et al., 2018), water management (Hallouin et al., 2018; Phan et al., 2016) and ecosystem services modelling (Zeng and Li, 2019). Landuyt et al. (2013) conducted a SWOT analysis of modelling techniques for ecosystem services and suggested the BN methodology as well suited for ecosystem-related assessment, despite some limitations and weaknesses. Similarly, Uusitalo (2007) identified the BN as an effective approach for complex environmental modelling and management problems having high specificity requirements. However, the key attributes for an adequate assessment of coral reefs health and resilience necessities the BN model to be quantified using multidisciplinary, data-induced, evidence-based, and expert-driven approaches. In light of these requirements, this study requires to further advance previous BN modelling frameworks for reef management, such as Gilby et al. (2016) and Brown et al. (2017), by integrating long term climate scenarios with local pressures from increasing human use and land-management. Additionally, the exploitation of structural analysis in a sequential integration procedure coupled with other modelling techniques in a stepwise manner enables modelling needs and requirements to be addressed more effectively (Suprun et al., 2018).

This paper presents a novel probabilistic scenario-based modelling approach using hybrid exploitation of the BN and structural analysis techniques using qualitative and quantitative data to investigate the long-term impacts of climatic and non-climatic pressures, together with a range of management response strategies, on the health and resilience of coral reefs for the time horizon of 2070. While the resilience of coral reefs represents the recovering capability of reef systems to recover towards a coral-rich state from either climatic or non-climatic pressures disturbance as a result of extreme events (Hughes et al., 2017). In addition, reef system resilience can be referred to their resisting or maintaining capacity against shifting from the morphological diversity towards single coral morphology or algal dominance (Scott et al., 2015). However, the health and resilience of coral reefs is relative to the coral cover in the study zone in this study. The Representative Concentration Pathways (RCP)s (IPCC, 2014) were used as the basis for different climatic scenarios to explore the implications of climate change impacts.

Section snippets

Case study location

Tanna is a relatively small island (550 km2) in Tafea Province, State of Vanuatu (in the Melanesian Pacific islands), in the South Pacific Ocean, with a rapidly increasing population largely living in traditional village communities (Buckwell et al., 2019). (Elliff and Kikuchi, 2017). Coral reefs are subject to multiple anthropogenic pressures, which currently deliver vital ecosystem services to Tanna’s community, including improving the local economy through tourist attraction (Mackay et al.,

Modelling approach

The modelling approach and procedure were formulated by the multidisciplinary team of experts having skillsets from diverse and independent research fields including marine biology, coastal systems, climate change, systems modelling and risk assessment. Importantly, it should be noted that these experts had adequate knowledge of the study area and context since they were previously involved in a research project focusing on climate change resilience analysis and ecosystem and socio-economic

Delineation

Formation of the modelling team, formulation of the modelling approach and the definition of modelling scope including regional, temporal, and interdisciplinary boundaries were established throughout the delineation step. An extensive review of the literature on coral reef health and resilience was conducted to identify the key variables and stressors (see Supplementary File A).

Following this, a list of 23 key variables was selected from a list of variables (known as nodes in BN modelling)

Codifying layers and data collection

The following sub-sections outline the various nodes and supporting evidence used to quantify the model by completing nodes’ relationship functions or CPTs within the four DPSI layers. Readers are referred to Supplementary Files A and B for a detailed discussion of the node definitions and supporting evidence.

Scenario setting

Once the model quantification was accomplished, scenario settings were defined to conclude the modelling procedure with the last phase. Scenario-based analyses aimed at predicting the health and resilience of coral reefs in response to the management strategies and prospective scenarios covering both direct and indirect anthropogenic as well as climatic disturbances by 2070. Scenario nodes’ states were changed to compare the target node of persisting or declining coral reef health and

Results and discussion

By the completion of the model and the accomplishment of meaningful scenario settings, the health and resilience conditions under each scenario for all four RCPs were projected. Scenario predictions showed the probability of both persisting and declining states. The scenario predictions show the probability of ecosystem condition for the time horizon of 2070. The results of this scenario-based modelling can provide decision-makers and stakeholders with a more holistic view and new insights into

Conclusion

This study explored the long-term perspective of the future health and resilience condition of coral reefs under different combinations of management strategies and under four climate change RCPs. A BN model was developed through a systematic approach by following a stepwise modelling procedure. Subsequently, twelve scenario settings were defined based on the effectiveness or the extent of management strategies, climate change trajectories, and future population projections. The presented

CRediT author statement

Mehdi Hafezi: Conceptualization, Literature review, Data curation, Methodology, Software, Writing- Original draft preparation.

Oz Sahin: Data curation, Methodology, Investigation, Writing- Original draft preparation, Reviewing and Editing.

Rodney A. Stewart: Methodology,Validation, Writing- Original draft preparation, Reviewing and Editing.

Rod M. Connolly: Data curation, Validation, Reviewing and Editing.

Brendan Mackey: Reviewing, Editing and Supervision.

Daniel Ware: Reviewing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research was conducted as part of the EcoAdapt Project which is funded by a private charitable trust that wishes to remain anonymous. The donor had no input or influence on any aspect of the design, implementation, analyses or documentation of the research reported here.

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