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

Uncovering the drivers that shape biodiversity patterns is critical to understand fundamental ecological and evolutionary processes, but also to assist biodiversity managers and conservation agencies. Despite evidence that biodiversity composition is influenced by processes at different spatial scales, little is known about the role of fine-scale oceanographic processes in controlling marine biodiversity patterns. This is particularly important in biodiversity hotspot regions, where small changes in local conditions may facilitate introductions of novel species, local extirpation, or even extinction. Here, we conducted oceanographic modelling and environmental DNA (eDNA) metabarcoding to investigate how fine-scale oceanographic processes shape marine biogeographic patterns across the Galápagos Islands. We found that eDNA data confirmed previously reported biogeographic regionalization, and demonstrated significant differences in community structure across the highly diverse oceanographic seascape of the Galápagos Islands. We then tested the effect of local current systems with a novel metric, termed oceanographic resistance, measuring the cumulative seawater flow resistance between pairs of geographic sites. Oceanographic resistance explained a significant proportion of variation in eDNA-measured beta dissimilarity between sites (2.0% of total), comparable in influence to some of the most important abiotic drivers, such as temperature (2.9%) and geographic distance between sites (11.5%). This indicates that oceanographic resistance can be a useful metric to understand the effects of current systems on marine biota. Taken together, 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.