Original article Intermediate tidal stress promotes the detritivore-mediated decomposition of Spartina litter Anett Pfauder, Martin Zimmer * Zoologisches Institut, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany Available online 18 October 2005 Abstract Saltmarshes, functionally important habitats in the marine–terrestrial ecotone that are regularly affected by tidal inundation, are mainly detritus-based in terms of fluxes of nutrients and energy. With respect to the mediating influence of saltmarsh detritivores on microbial colonisation of detritus and on decomposition processes, we tested whether the “intermediate disturbance hypothesis” (IDH) is also applicable to the effects of stress in this stressful environment. Decomposition experiments with litter of the cord- grass, Spartina anglica, and with terrestrial [Porcellio scaber (Isopoda)] and marine/semi-terrestrial [Orchestia gammarellus (Am- phipoda)] detritivores as well as animal-free controls were carried out in an artificial saltmarsh system. Different daily flooding regimes served as experimental levels of stress. Both litter mass loss and microbial respiration were mostly higher under aquatic than under terrestrial conditions, no matter whether detritivores were present or not. Considering the intertidal zone, low to inter- mediate daily inundation rates resulted in increased microbial respiration and an increased influence of detritivores on litter mass loss in early stages of cordgrass decomposition with high rates of detritus mass loss, and intermediate tidal stress led to higher microbial cell counts throughout the entire experiment. Summarised over 3 months, regression analyses suggested that microbial activity and detritus mass loss show a trend towards highest values at low inundation rates and under permanent inundation, although microbial density was higher under longer daily inundation. Access to detritus by detritivores enhanced both litter mass loss and microbial respiration, especially in later decomposition stages, whereas microbial density was reduced by detritivores. In conclusion, we predict that overall the decomposition of cordgrass detritus in saltmarshes is promoted in the intermediate to high area of the intertidal zone with daily inundation of ca. 4–10 hours where both marine and terrestrial detritivores have access to promote decomposition processes through feeding and mediating microbial activity. © 2005 Elsevier SAS. All rights reserved. Keywords: Spartina anglica; Decomposition; Detritivores; Terrestrial; Marine; Porcellio scaber; Orchestia gemmarellus 1. Introduction Saltmarshes, ecologically connecting coastal waters and the terrestrial coastline fringe, are dominated by harsh, but predictable, environmental conditions caused by regular tidal inundation [5,10]. It has been argued over decades as to how to distinguish between stress and disturbance (for discussion, see [16]), but according to the definition of disturbance by several influential papers—e.g. [8,9,12,14–16]—tidal cycles have to be considered stress rather than disturbance. Although salt- marsh inhabitants are expected to be adapted to the flooding regime, the cyclic submersion and emersion of their intertidal habitat still poses stress on them; http://france.elsevier.com/direct/ejsobi European Journal of Soil Biology 41 (2005) 135–141 * Corresponding author. Fax: +49 431 880 4153. E-mail address: mzimmer@zoologie.uni-kiel.de (M. Zimmer). 1164-5563/$ - see front matter © 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.ejsobi.2005.09.007