A parasite indirectly impacts both abundance of primary producers and biomass of secondary producers in an intertidal benthic community

The New Zealand cockle Austrovenus stutchburyi is often found stranded on the sediment surface due to infections by echinostome trematodes. High densities of heavily-infected cockles on the sediment surface a¡ect near-seabed hydrodynamics and sedimentation and, in turn, benthic animal community structure and diversity. In a six-month ¢eld experiment on an intertidal sand£at we manipulated the density of cockle mimics on the sediment surface, and here we show that their presence had two signi¢cant impacts on community functioning. First, the benthic primary production (in terms of chlorophyll-a content) was reduced by 8^22%. Second, their presence signi¢cantly boosted (up to 5-fold) the secondary production (in terms of biomass) of Coelenterata, Nemertea, small polychaetes, small bivalves and the gastropod Diloma subrostrata. The results hence provide a ¢eld experimental example of a parasite-mediated link between diversity and productivity.