Assessing impacts of natural and anthropogenic stress on macrobenthic communities in a coastal upwelling system

Human induced eutrophication leading to hypoxia is increasingly impacting coastal areas. Coastal upwelling systems are naturally highly productive, making it difficult to distinguish between organic matter inputs derived from natural processes and anthropogenic disturbances. This concept is newly characterised here as the “Upwelling Ecosystem Quality Paradox”. Soft-bottom macrobenthic communities have been widely used as indicators for the detection of impacts of disturbances on the biota. I evaluated the performance of several biotic indices to assess ecological conditions in a Northern Chile bay subject to natural upwelling that displays naturally shallow hypoxia and hosts an industrial hub. Results highlight limitations of commonly used indices, especially those based on pre-existing sensitivity classifications. An index that compares taxonomic abundances from study sites with selected reference stations permitted a drastic reduction in the influence of natural conditions. A new functional index is proposed that provides early detection of ecological degradation.Benthic community functioning is described along a natural depth gradient of organic matter enrichment. Filling gaps of knowledge for these benthic communities helps to support appropriate management decisions to limit adverse effects of severe hypoxia and anoxia. Long term and continuous monitoring of atmospheric, oceanographic, biogeochemical and biological processes through international collaborations of science and society appears required to reach such an aim. The conservation of upwelling ecosystems and the exceptional life they support is necessary to continue receiving the many benefits associated from these key ecosystems.