ecosystems

MSc thesis report

The coral reefs of Bonaire, providing resources and environmental services, are often ranked among the richest, most resilient and least degraded in the Caribbean, but they are not escaping the global degrading trend in coral reefs. Identifying and combatting local stressors, increases the resilience to global stressors. Research has shown that even the deeper, relatively unexplored reefs, mesophotic coral ecosystems (MCE), ranging from 30 to 150m in depth, are being impacted by anthropogenic disturbances. As the MCEs start where Scuba diving stops, and submersibles are often too costly, this study deployed an ROV to explore and monitor the shallow (5-20m) and the upper-mesophotic (40- 60m) reefs at eight sites along the leeward coast of Bonaire. These sites were subdivided into different zones, showing a gradient in human impact and water quality. The imagery obtained by the ROV is of adequate quality, allowing for identification to genus level if not species level, and showed comparable results in estimated percentage coral cover with other recent studies. The benthic community composition changed along the vertical (depth) and horizontal (human impact and water quality) gradient. Benthic cyanobacterial mats were found around 40-60m depth, covering large parts of the ocean floor. Hard and soft corals, sponges, macroalgae and crustose coralline algae occurred at 40m depth at six of the eight monitored sites, indicating the presence of MCEs, and only at one site (Karpata), hard corals were present at 60m depth. Coral cover showed a clear increasing trend with decreasing human impact, addressing the need for a better understanding of heterogeneity among sites and local conservation measures. Developments in underwater robotics and machine learning enable more research on these hidden coral reefs and identification of the effect of local stressors on MCEs.

Small islands are particularly vulnerable to climate change because of their fragile ecosystems, small economies, and often extensive, low-lying coastal areas.

Therefore, small islands, such as present in the Caribbean Netherlands, are expected to suffer excessively from rising temperatures, changes in precipitation, sea level rise, coral bleaching, cyclones, droughts and floods. Yet, scientific evidence of these effects in the Caribbean Netherlands is scarce.

In this study, an analysis is conducted assessing the impacts of climate change for the island of Bonaire. A mix of methods is used to estimate the impacts of climate change, including climate and flood models, ecological-economic models, as well as social-science methods such as social media analysis and participatory mapping. Four sub-studies can be distinguished: the estimation of the biophysical impacts, the modelling of economic effects, the identification of socio-cultural effects, and the exploration for potential adaptation options.

The main findings of the study include the following:

• Already by 2050, sea level rise will cause permanent inundation of parts of the low-lying nature reserves of the saliñas, Lac Bay and Klein Bonaire. The flooded surface area will increase further by 2150, threatening Bonaire's high-risk built-up areas such as Belnem and other areas in Kralendijk. The loss of coral reefs as a natural buffer will amplify these effects.
• The economic impact of climate change is mainly felt through damage costs caused by floods as well as negative effects on tourism caused by the loss of corals. Storms and floods are expected to cause an estimated damage costs of US$317 million by 2050. The degradation of coral reefs leads to the degradation or loss of the majority of dive sites on Bonaire, which may cause a reduction in tourist arrivals of more than 100 thousand visitors.
• Climate change is also expected to severely cause loss of cultural heritage and health impacts on Bonaire. Among others, this includes the permanent flooding of key locations with cultural significance for Bonaireans, such as the slave huts and the house at Boca Slagbaai. Additionally, climate change is expected to affect Bonaireans’ health, such as changes in vector-borne disease incidence and heat-related stress.
• Potential adaptation strategies against climate change on Bonaire include nature-based solutions such as the conservation of coral reefs and the restoration of coastal vegetation, which contribute to the prevention of flooding. We conclude that, although the impacts of climate change necessitate immediate action, decision-makers should also focus on the longer term, such as 2150 and beyond, as the effects of climate change will worsen significantly over time.

For more information about the study or sub-studies, download the following reports:

• Synthesis report
• Impacts of climate change on coastal inundation on Bonaire
• Coral reef degradation and the impacts on tourism and economic development
• Impacts of climate change on the built environment
• Impacts of climate change on cultural heritage
• Impacts of climate change on public health
• Adaptation strategies against coastal flooding