Applying a ridge-to-reef framework to support watershed,water quality,and community-based fisheries management in American Samoa

Water quality and fisheries exploitation are localized, chronic stressors that impact coral reef condition and resilience. Yet, quantifying the relative contribution of individual stressors and evaluating the degree of human impact to any particular reef are difficult due to the inherent variation in biological assemblages that exists across and within island scales. We developed a framework to first account for island-scale variation in biological assemblages, and then evaluate the condition of 26 reefs adjacent to watersheds in Tutuila, American Samoa. Water quality data collected over 1 year were first linked with watershed characteristics such as land use and human population. Dissolved inorganic nitrogen (DIN) concentrations were best predicted by total human population and disturbed land for watersheds with over 200 humans km⁻², providing a predictive threshold for DIN enrichment attributed to human populations. Coral reef assemblages were next partitioned into three distinct reeftypes to account for inherent variation in biological assemblages and isolate upon local stressors. Regression models suggested that watershed characteristics linked with DIN and fishing access best predicted ecological condition scores, but their influences differed. Relationships were weakest between coral assemblages and watershed-based proxies of DIN, and strongest between fish assemblages and distances to boat harbors and wave energy (i.e., accessibility). While we did not explicitly address the potential recursivity between fish and coral assemblages, there was a weak overall correlation between these ecological condition scores. Instead, the more complex, recursive nature between reef fish and habitats was discussed with respect to bottom-up and top-down processes, and several ongoing studies that can better help address this topic into the future were identified. The framework used here showed the spatial variation of stressor influence, and the specific assemblage attributes influenced by natural and anthropogenic drivers which aims to guide a local ridge-to-reef management strategy.