Functional redundancy of primary producers mitigates function loss in an ice-scoured eelgrass meadow (Zostera marina, Linnaeus 1758)

In boreal and subarctic regions, sea ice scouring increases benthic heterogeneity of shallow coastal ecosystems. The ice foot can trap eelgrass (Zostera marina) leaves and sediments, and, as it breaks, patches of vegetation are either displaced or destroyed, creating a mosaic of vegetated and bare sediment habitats. This spatial heterogeneity reflects on environmental differences where biodiversity and ecosystem functioning (BEF) relationships can diverge. This study aims to explore the relationships between biodiversity and functioning in the boreal ice-scoured eelgrass meadow of Rimouski Bay (Québec, Canada). We assessed changes in diversity of the macrobenthic community and ecosystem functioning (based on carbon, oxygen, and nutrient fluxes) in 9 bare sediment and 9 vegetated cores sampled from the meadow, over a 20-day experiment. We hypothesized that bare sediment would exhibit lower species density, richness, and community functioning than vegetated habitats. Indeed, the absence of the foundation species Z. marina resulted in a less diverse macrofaunal community, as abundant in both habitats tough. During immersion, net community production and respiration were five-times higher in vegetated cores at the beginning of the experiment. However, this gap decreased by two throughout the experiment due to the natural recruitment of green algae (Ulva) and its functional redundancy in primary production. However, the non-perennial nature of Ulva questions functional redundancy all year long continuity, showing the need to integrate seasonal fluctuations in biodiversity and functioning assessment informing BEF theory.