Leaf size doesn’t matter: environment shapes eelgrass biodiversity more
than a foundation species’ traits.
Abstract
Aim: Understand the ecological processes that shape community
composition in eelgrass meadows along the coast of France at local and
regional scales. Location: Northeastern Atlantic. Methods: Combining
taxonomic and trait-based approaches with structural equation modeling,
we explored the mechanisms governing community assembly in five meadows
located over a distance of 800 km along the French coast in the
Northeast Atlantic. We assessed the spatial variability of
eelgrass-associated invertebrate communities as affected by
environmental parameters or morphological traits of the eelgrass and
linked these mechanisms to their impacts at local and regional scales
through analyses of the taxonomic and functional α and β diversities. We
then quantified the direct and indirect effects of environmental factors
on macrofaunal structure and composition. Results: Eelgrass meadows
locally favored higher species abundance, diversity, and functional
traits present in the community relative to nearby bare sediments. At
the regional scale, eelgrass diversity was comparable between sites,
with high species turnover observed among them, and each site being
characterized by different species and different sets of traits. These
differences were due in part to morphological traits of the meadows, but
the explanatory variables that best explained the differences among the
meadows were environmental conditions, including temperature, current
velocity, and Δ water level. Main conclusions: Meadows appear to harbor
subsets of species from the regional species pool, rather than harboring
eelgrass-specific assemblages. The processes that maintain seagrass
diversity appear to reflect a seascape-scale meta-community composed of
many habitats connected by source-sink dynamics. Given that eelgrass
enhances the diversity and abundance of species found in neighboring
habitats, conservation programs should consider ecosystem-level
protection spanning multiple habitats, including eelgrass, in order to
maximize the protection of biodiversity.