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The contribution of aquatic shredders to leaf litter decomposition in Atlantic island streams depends on shredder density and litter quality
It is widely reported that shredders play an important role in leaf decomposition, especially in continental temperate streams.However, the paucity of shredders in many oceanic island streams leads to a relative greater contribution of microbes to litter decomposition in these streams. We investigated the importance of shredder presence and density (three levels) and leaf litter identity (Alnus glutinosa, Clethra arborea and Acacia melanoxylon) on leaf litter decomposition in one stream located in the Azores archipelago. Coarse and fine mesh bags were used, respectively, to allow natural colonization of leaf litter by macroinvertebrates or to exclude macroinvertebrates. Treatments with 1 and 3 shredders were accomplished by enclosing 1 or 3 shredders in fine meshes. Litter decomposition rates significantly differed among shredder density treatments only for A.glutinosa and C.arborea. Decomposition rates were significantly faster for the natural shredder density treatment than for other shredder treatments. Shredder density significantly differed among litter species being higher in A.glutinosa than in C.arborea and A.melanoxylon. We show that when shredders are present in high densities in oceanic island streams they can substantially contribute to the decomposition of high quality leaf litter, while the decomposition of hard leaf litter is mostly carried out by the microbial community.
MF18020 Accepted 20 February 2018
© CSIRO 2018