What defines an edge? : quantifying edge effects across multiple trophic levels

Habitat fragmentation is often cited as a primary driver of biodiversity loss across biomes. Spatial habitat fragmentation causes an increase in edge habitat relative to interior which may provide different value as they often vary in functionality. There is a general lack of consensus regarding the distance that delineates edge versus interior limiting the ability to accurately capture edge effects on seagrass ecological function. As fragmentation is accelerating, it is necessary to understand the factors driving edge effects to better predict the effect of changes in habitat configuration. My work measured community metrics in seagrass ecosystems at varying distances from the edge to understand edge effects driving organismal response to habitat fragmentation. First, I sampled seagrass beds in 2018 for a post-disturbance study one year after Hurricane Harvey hit Texas. I sampled along seagrass patch edges and interior to quantify seagrass morphometrics and biomass, benthic macrofauna and nekton communities. Next, I conducted a fine-scale study in 2019 sampling seagrass beds along 10 meter transects from the edge in towards bed interiors in the same region to quantify nekton and macrofaunal communities, seagrass metrics, predation risk, and flow at a precise scale. Across both studies, I found increased seagrass biomass in habitat interiors that was most pronounced around 2 meters in one study. I saw higher temperature and epiphyte biomass with increased distance from seagrass edge in the fine-scale study and across studies there were no demonstrated edge effects on benthic macrofaunal community composition, predation risk or flow. There was a positive effect on nekton diversity in the post-disturbance study driven by matrix spillover of species associated with soft muddy bottoms. Results suggest pronounced edge effect for seagrass itself, and ecologically defined edges may be larger than the edge sizes assumed in many past studies highlighting the need for edge designations to be scaled to the response variables tested in order to accurately capture edge effects. Multi-trophic and continued empirical measurement of habitat edges may help resolve differential responses across studies and predict the effects of anthropogenic habitat fragmentation on the ecological function of critical nearshore habitat like seagrassMarine Scienc