Abstract
Seagrass beds provide a variety of ecosystem services, some of which accrue outside the bounds of the habitat itself. Here we use environmental DNA (eDNA) amplicons to analyze the temporal and spatial effect of eelgrass (Zostera marina) on the immediately surrounding ecological community. Sampling seawater along transects extending outward from eelgrass beds, we demonstrate that eDNA provides meter-scale resolution of communities in the field. We evaluate eDNA abundance indices for twelve major phylogenetic groups of marine and estuarine taxa along these transects, finding highly local changes linked with proximity to Z. marina for a diverse group of dinoflagellates. Eelgrass habitat consistently and dramatically limits dinoflagellate abundance both within the beds and for at least fifteen meters outside. Because many dinoflagellates are capable of forming Harmful Algal Blooms (HABs) toxic to humans and other animal species, the salutory effect of eelgrass habitat on neighboring waters has important implications for public health as well as shellfish aquaculture and harvesting.