Drivers of macroalgal-epifaunal community structure on temperate rocky reefs in California, USALong-term Temporal Trends

Inez Mangino¹, Robert J. Miller¹

¹University of California, Santa Barbara, USA

Macroalgae are foundational to rocky reef ecosystems, providing complex, three-dimensional structure that supports diverse reef communities. Epifaunal invertebrates form dense populations on macroalgae, utilizing them for habitat, food and refuge from predation. These ubiquitous epifauna contribute significantly to secondary production and serve as a key energy source for higher-order reef consumers. Understanding the long-term temporal dynamics of macroalgal-epifauna communities (MECs) and how local and regional-scale environmental drivers influence them is essential for advancing our knowledge of marine food webs and ecosystem function, yet remains largely unexplored. Therefore, we analyzed how environmental predictors including sea surface temperature, wave height and nutrient availability influence MECs over a 16-year time series from three rocky reefs on Santa Cruz Island (Santa Barbara, California, USA). We used structural equation modeling (SEM) to evaluate both direct and indirect effects of environmental drivers on epifaunal species diversity, richness and abundance. SEM enables us to determine whether environmental changes influence epifaunal invertebrate communities directly or indirectly, through changes in the macroalgal habitat. This research provides valuable insights into the environmental drivers of epifaunal variability within macroalgal communities on rocky reefs and enhances our ability to predict how benthic communities may respond to future environmental and climate change scenarios.