Abstract
Similar to other coastal biogenic habitats (e.g. tidal marshes, kelp forests, mangroves and coral reefs), a key function of seagrass meadows is the enhancement of biodiversity. Variability at multiple spatial scales is a driver of biodiversity, but our understanding of the response of macrofauna communities to variability of seagrass meadows is limited. We examined the macrofauna community structure (abundance and biomass) and diversity patterns (α- and β-diversity) across a seascape gradient of eleven seagrass meadows differing in the number, composition and density of plant species. The variability of the macrobenthic communities was regulated by a combination of sedimentary (mainly for the infauna) and macrophyte (mainly for the epifauna) predictors. We demonstrate that the natural occurrence of drifting algae trapped in the aboveground complexity of the meadows benefits seagrass macrofauna. Seagrass-associated macrofauna showed a clear increase in abundance and α-diversity metrics with increasing habitat complexity attributes (i.e. shoot density, plant biomass and canopy height). Furthermore, partitioning of β-diversity (i.e. the variation of species composition between sites) implied the replacement of some species by others between sites (i.e. spatial turnover) instead of a process of species loss (or gain) from site to site (i.e. nestedness). Therefore, the enhancement of macrofauna diversity across an increasing gradient of seagrass complexity, and the dominance of the turnover component suggest that devoting conservation efforts on many different types of meadows, including the less diverse, should be a priority for coastal habitat-management.
Highlights
Seagrass meadows influence key coastal processes such as productivity, filtering, carbon sequestration, and food webs, turning these coastal habitats into one of the highest global economic assets among natural ecosystems (e.g. Boström et al 2006a, b; McGlathery et al 2007; Duarte et al 2010; Fourquerean et al 2012)
The macrofauna communities associated with seagrass meadows have been studied extensively, and clear evidence of macrofauna community variability has been documented at different spatial scales (e.g. Hovel and Lipcius 2002; Borg et al 2010; Boström et al 2011)
Sedimentary characteristics across a seascape gradient of seagrass meadows The Non-metric multidimensional scaling (nMDS) ordination of the sedimentary characteristics indicated a separation of the different sites (ANOSIM; R 2 = 0.630; p < 0.001) along the spatial gradient (Fig. 1; Fig. 2a)
Summary
Seagrass meadows influence key coastal processes such as productivity, filtering, carbon sequestration, and food webs, turning these coastal habitats into one of the highest global economic assets among natural ecosystems (e.g. Boström et al 2006a, b; McGlathery et al 2007; Duarte et al 2010; Fourquerean et al 2012). The macrofauna communities associated with seagrass meadows have been studied extensively, and clear evidence of macrofauna community variability has been documented at different spatial scales (e.g. Hovel and Lipcius 2002; Borg et al 2010; Boström et al 2011). In the case of the Baltic Sea, the aquatic flora is represented by a diversity of meadows ranging from monospecific patches dominated by high-biomass species, such as Zostera marina and Ruppia spp, to a different mixture of limnic species (e.g. Kautsky 1988; Gustafsson and Norkko 2019). This rich range of plant biodiversity is known to influence coastal ecosystem functioning (Gustafsson and Boström 2011)
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