Reef biodiversity and urbanization

Home for thousands of species, coral reefs are one of the most productive and diverse ecosystems in the world. These habitats provide services and resources to human populations, including coastal protection, tourism, pharmacology, and seafood. However, urbanization can decrease marine genetic diversity and ecological functions. Examples of measures of anthropogenic impacts on reefs include distance from heavily populated areas or from treated wastewater input, significant fishing pressure, and coastal development (e.g., reclaimed land, road construction, artificial reefs, or dredging). Thus, it is crucial to evaluate and monitor changes in coral reef communities under distinct impact levels. A major challenge for researchers has been in quantifying diversity; traditional methods such as visual census, photoquadrats, or collection of tissues have several constraints. A very recent and revolutionary tool is environmental DNA (eDNA). For example, DNA filtered from seawater is accurate in detecting local biodiversity without the need to capture or directly observe organisms. However, eDNA surveys at large geographical scales are still missing. In this study, we used eDNA to address how urbanization affects coral reef biodiversity. Our global sampling surveys included relatively pristine to more densely populated sites, including regions of Brazil, Hawai‘i, Hong Kong, Niue, Okinawa, and Palmyra Atoll. At each location, we sampled and filtered seawater from several coral reefs. Using multiple metabarcoding markers, we characterize the diversity of microbes, invertebrates, and reef fishes. We then analyze the dissimilarity of genetic diversity and functional groups between regions and sites. Additionally, using an extensive literature review, we compile population and environmental data for these sites and build urbanization indices. We use coefficient models to evaluate the influence of urbanization levels on the biodiversity metrics. Together with collaborators from the local communities and governmental and non-governmental organizations, we aim to evaluate how eDNA surveys can support the monitoring and management of reef ecosystems.