Spatial Variability in Species and Functional Diversity of Nearshore Fishes Exceeds Variability Related to Shoreline Armor in an Urbanized Estuary

Abstract One important measure of biodiversity is functional diversity within a given assemblage, because it provides information about the collective roles that species play in an ecosystem. The expressed functional diversity of an assemblage can be thought of as realized niche space occupied by species present, shaped in part by characteristics of the available habitat. Assessing functional traits can therefore provide some indication of the ecological significance of different habitat features, and how habitat modification may impact community structure. Here, we assessed the functional diversity of fish across the Salish Sea, Washington, USA adjacent to shorelines of different degrees of anthropogenic impact via shoreline armor. We found differences in assemblage composition between shorelines from northern and southern sites, for example Pacific herring and Pacific tomcod were more abundant at northern sites, while three-spined stickleback were most abundant at southern sites. However, we found no equivalent trend in functional diversity between these groups, nor did we find any variation in metrics of taxonomic or functional diversity among coastal fish assemblages based on shoreline condition (natural, armored or restored). Although we detected some local variation in species richness, functional richness, and functional evenness, these differences did not appear to be structured by broader spatial context. This work represents the first broad-scale assessment of the functional diversity of fishes in the Salish Sea and informs our understanding of the degree to which nearshore fish assemblage structure varies in response to shoreline conditions within an urbanized estuary.