Ecosystem Vulnerability and Mapping Cumulative Impacts on Hawaiian Reefs

Abstract

The nearshore reef environment in Hawai‘i is impacted by a wide range of human activities. As a result of these anthropogenic stressors, economic and sociocultural benefits to communities in Hawai‘i have diminished over time. Understanding the spatial distribution, intensity, overlap, and cumulative impact of human activities is essential for effective marine management and protection of ecosystem services generated by coral reefs. Currently, this kind of information is not readily available to resource managers and policy makers in Hawai‘i. This research used existing data and novel approaches to produce maps for some of the most important anthropogenic stressors on coral reefs in Hawai‘i. To accomplish this, I compiled a comprehensive database, synthesized a suite of spatial datasets into a unified framework, and devised geospatial methodologies to produce statewide maps of anthropogenic stressors including: fishing pressure, land-based pollution, habitat modification, invasive species, marine debris, and climate change. Expert knowledge surveys were conducted to assess the vulnerability of three nearshore habitat types to anthropogenic stressors. The resulting vulnerability weighting factors for stressor-habitat pairs were used to produce continuous maps of cumulative impacts across the Main Hawaiian Islands. Experts ranked fishing as the most impactful stressor to coral dominated and other hard bottom habitats. Invasive species were another major concern for Hawai’i experts, which differs from other global surveys of coral reef experts. Coral dominated hard bottom habitat was both the most vulnerable to stressors and the most impacted across the Main Hawaiian Islands. Human population density was shown to be a poor proxy for this approach to map cumulative anthropogenic impacts. Spatial datasets developed by this study are available for use in future research on patterns of reef state and coral reef degradation. These maps also directly benefit management by identifying what places and habitat types are most impacted, which drivers should be of greatest concern in different areas, and where different management strategies (e.g., regulations, restoration, enforcement, or increased monitoring) should be prioritized.