Eelgrass habitat structure affects epifaunal biodiversity and community composition but not the distribution of functional traits among taxa

Habitat structure strongly influences faunal assemblages, but the relative roles of structural characteristics across different spatial scales in driving community structure and composition are not well understood. In this study, we extensively sampled a Southern California eelgrass Zostera marina L. seascape to determine which aspects of seagrass habitat structure exert the greatest influence on epifaunal density, diversity, community composition, and functional trait distribution. We use generalized linear models, generalized additive models, distance-based redundancy analysis, and fourth-corner analysis of trait distribution to model the relationships between epifaunal communities and features of eelgrass seascapes at microhabitat scales (e.g. shoot and epiphyte biomass) and patch scales (e.g. patch area, distance to edge, and percent eelgrass cover). We found that total epifaunal density and diversity were most strongly correlated with eelgrass shoot biomass and weakly correlated with patch area and eelgrass percent cover. Distance to the nearest patch edge explained very little of the variability in epifaunal density and diversity. In contrast, community taxonomic composition was most strongly driven by local shoot density and the availability of eelgrass habitat at larger scales as measured by the percent of eelgrass cover in the surrounding seascape. We found no evidence for effects of eelgrass habitat structure at any scale on epifaunal community functional composition. Our results demonstrate that epifaunal communities are influenced more by the amount of seagrass habitat than its configuration, but that the scale at which the amount of habitat is relevant depends on the community characteristic in question.