Species-specific patterns of litter processing by terrestrial isopods (Isopoda: Oniscidea) in high intertidal salt marshes and coastal forests

1. The species-specificity of litter processing by three species of isopods at the interface between salt marsh and coastal forest habitats in the south-eastern United States was examined. 2. To quantify isopod performance, measurements were taken of feeding, digestion and growth of isopods fed on three litter types ( Juncus roemerianus , Quercus virginiana and Pinus palustris ) and on artificial diets containing one of three classes of model phenolic compounds (simple phenolics and hydrolysable and condensed tannins). 3. To quantify the ecosystem impact of isopods, promotion of microbial respiration, changes in detritus chemistry, and the quantity of litter processed by isopod populations were measured. 4. The results support three hypotheses concerning isopod–litter interactions. (i) Isopod performance on different litter types can be predicted based on chemical litter traits, e.g. phenolic concentrations and C : N ratios. (ii) Fully terrestrial isopods are better adapted to the range of phenolics found in angiosperm litter than are semiterrestrial species inhabiting the supralittoral. (iii) Isopod species differ with respect to their impact on decomposition processes due to species-specific digestive capabilities, different effects on microbial decomposition and different rates of net litter processing. 5. Because isopods are transitional between semiterrestrial and terrestrial habitats, unlike most other salt marsh detritivores, they are likely to play a unique role in decomposition processes and in the flux of materials between salt marsh and terrestrial habitats.