Nutrient cycles in both terrestrial and many freshwater habitats are fueled by terrestrial detritus. However, direct comparisons of decomposition processes in these environments are scarce. Aiming at shedding light on similarities and differences in these processes in different habitats, we studied decomposition of low-quality versus high-quality detritus through the action of shredders versus grazers in aquatic versus terrestrial microcosms under controlled climatic conditions. Decomposition processes were most strongly affected by whether they took place in the terrestrial or the aquatic environment: Leaching resulted in a rapid mass loss of detritus in the aquatic environment, and detritus traits became less pronounced over time. Thus, breakdown was mediated through dissolved organic matter (DOM) in water but through particulate organic matter (POM) on land. Litter mass loss and the promoting effects of detritivores on mass loss also depended on the environment, but shredders always had a greater effect than grazers. Both litter and detritivore diversity were overall of little relevance for litter mass loss, but more so in the aquatic than the terrestrial environment. By contrast, the influence of detritivores on microbes was stronger in water than on land, but effects depended on the litter type. The type of both litter and detritivores, however, was less significant in the aquatic than in the terrestrial environment, possibly due to leaching and abiotic processing of litter during early decomposition, resulting in diminishing differences between litter types. We conclude that the habitat type shapes the dynamics of leaf litter decomposition. Heavy leaching (in the aquatic environment) shortens initial decomposition phases and dislocates the degradation of easily accessible compounds in the form of DOM from the leaves into the water column. Consequently, initial interspecific differences in litter quality diminish, and both functional differences in, and diversity of, both litter and detritivores become less important than in the terrestrial environment.

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Sandy beaches are characterised by heterogeneously distributed food sources both in time and space. The major energy supply is derived from marine subsidies in the form of beach-cast macrophyte wrack. Wrack patches are short-lived, and their position on the beaches varies with tidal and seasonal cycles as well as weather conditions. Little is known about how sandy beach inhabitants orient themselves towards, and colonise, wrack patches. In a series of field studies on islands off Vancouver Island (British Columbia, Canada), colonisation patterns of wrack patches by beach fleas and sand hoppers (Amphipoda: Talitridae), the most abundant macrofaunal detritivores, were studied. As indicated by colonisation of experimental patches of wrack and wrack surrogates that were either visible or buried in the sand, beach fleas (Traskorchestia traskiana) rely on olfactory cues for locating freshly deposited wrack patches in their patchy and dynamic habitat. Dense colonisation of freshly deposited algal wrack generally occurred within less than 1 h but depended upon the tidal height of wrack patches. Beach flea density in freshly deposited wrack patches increased with increasing tidal height. By contrast, sand hoppers (Megalorchestia californiana) colonised freshly deposited wrack patches in densities that decreased with tidal height. Discussing these interspecific differences, we provide a primer for future detailed studies on transport of matter along the marineterrestrial gradient of sand beaches.

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