Autonomous Reef Monitoring Structures (ARMS) Reveal Human-Induced Biodiversity Shifts in Urban Coastal Ecosystems

Biodiversity thrives in coastal marine habitats which host foundational species such as corals, mangroves, and seagrasses. However, coastal development and the growth of megacities along shorelines impose an array of stressors on the marine environment. These stressors inevitably impact biodiversity which dictates ecosystem functions and services. Despite extensive research on biodiversity responses to anthropogenic stressors, phylum-specific resistance and resilience dynamics - particularly in coastal marine ecosystems - remain poorly understood. Considering the global scale of coastal development, it is imperative to develop a more comprehensive understanding of how biodiversity, in terms of richness and community composition, is influenced by various anthropogenic stressors. Here, we present the first application of standardized Autonomous Reef Monitoring Structures (ARMS) as an experimental unit - using a common garden experimental design - to examine community responses to stress within an urbanized seascape. ARMS were seeded within two marine reserves for one year and then transplanted to sites of stress, including domestic sewage, and mariculture. We hypothesized that 1) human impacts reduce richness and alter composition of established communities; and 2) increasing intensity of these impacts reduces community resistance and resilience to stress. Using metabarcoding, we quantified richness and taxonomic composition and assessed their changes along an impact gradient. Our results showed that nutrient pollution, particularly inorganic nitrogen, significantly reduced species richness and restructured communities. Communities exhibited low resistance, yet high resilience - suggesting that urbanized seascapes have high recovery potential when stress is mitigated.