Role of seagrass physical structure in macrofaunal biodiversity-ecosystem functioning relationships

Seagrass above-ground shoot canopies and below-ground rhizome networks provide structurally complex habitat that supports diverse macrofaunal communities. Seagrasses also support biodiversity through their biological activity by influencing food availability. While numerous studies have demonstrated that seagrass physical and biological habitat elements influence macrofaunal diversity and community structure, we lack an understanding of how these elements potentially interact with sedimentary macrofaunal communities to influence ecosystem processes. To understand how physical seagrass structure affects macrofaunal biodiversity and the processes of carbon and nutrient cycling, we deployed artificial seagrass patches that mimicked canopies and surface rhizomes, in tandem with parallel observations of natural seagrass Zostera marina , unvegetated habitat, seagrass patch edge, and canopy control treatments. After 3 mo, we recorded rates of oxygen and nutrient flux from sediment cores and assessed macrofaunal biodiversity and environmental variables to relate them to benthic flux patterns. We found significantly higher macrofaunal abundance and diversity in natural seagrass treatments compared to unvegetated, patch edge, canopy control, and artificial seagrass treatments. However, we found no difference in benthic fluxes across all treatments, suggesting a lesser role for macrofaunal bioturbation in nutrient regeneration in these nearshore sediments. Our results also suggest lesser importance for the structural benefits of seagrasses than their biological contributions for supporting macrofaunal biodiversity. Negative edge effects on macrofaunal abundance and diversity suggest potential consequences for macrofaunal communities of fragmented seagrass habitats associated with anthropogenic disturbance.