Fine-scale oceanographic processes shape marine biodiversity patterns in the Galapagos Islands

Uncovering the drivers that shape biodiversity patterns is critical to understand ecological and evolutionary dynamics. Despite evidence that biodiversity composition is influenced by processes at different spatial scales, little is known about the role of fine-scale oceanographic processes on the structure of marine communities. This is particularly important in biodiversity hotspot regions, where small changes in environmental conditions may lead to substantial changes in species composition. We combined ocean modelling and 12S environmental DNA (eDNA) metabarcoding, targeting teleost and elasmobranch species, to explore if oceanographic processes influenced biogeographic patterns around the biodiverse Galapagos Islands. We first detected significant differences in eDNA-measured community structure across the archipelagos diverse seascape. We found no significant relationship between Lagrangian particle tracking metrics and nektonic biodiversity, and thus developed a novel metric to measure the cumulative seawater flow resistance between pairs of geographic sites. This metric explained a significant proportion of variation in eDNA-measured beta dissimilarity between sites, comparable in influence to important abiotic drivers, such as temperature and geographic distance between sites. Cumulatively, our results indicate that marine communities are particularly sensitive to changes in local current systems, and suggest that fine-scale oceanographic processes may have an underappreciated role in structuring marine communities globally.