Relationships between seagrass biodiversity and infaunal communities: implications for studies of biodiversity effects

Controlled experiments to elucidate links between ecosystem functioning and biodiversity have produced differing results. We investigate links between the species diversity in multispecies tropical seagrass beds in Thailand and the abundance, diversity and community structure of free-living nematodes within the beds. No relationship was found between seagrass diversity and nematode species richness or abundance, but a posteriori power analyses demonstrate that our sampling design had little prospect of detecting such relationships against a background of naturally occurring variability. We conclude that in a variable world biodiversity effects may be difficult to detect, even if they are large. Multivariate analyses show that there are relationships between seagrass diversity and the community structure of free-living nematodes, with different nematode assemblages occurring in patches of seagrasses with different numbers of seagrass species. We therefore conclude that biodiversity effects do exist in the real world. Different mixtures of seagrass species alter environmental conditions and food availability within the sediment through a range of processes (ranging from sediment trapping to interspecific differences in photosynthate production) which in turn affect differences in nematode community structure directly or through indirect pathways.