Environmental factors affecting Phragmites australis litterdecomposition in Mediterranean and Black Sea transitional waters

1. Leaf litter decomposition rates in aquatic ecosystems are known to be related to many abiotic and biotic factors. 2. Field experiments were carried out during spring 2005 in 16 ecosystems, each with four sampling sites, using the litter bag technique to investigate the influence of abiotic factors on patterns of reed litter breakdown in different physiographic, hydrological and physico-chemical gradients occurring in transitional water ecosystems in the Eastern Mediterranean and Black Sea. 3. Significant differences in leaf litter decomposition were observed among the studied ecosystems along univariate gradients of tidal range, water temperature, salinity and sinuosity index. 4. Overall, 71% of variance in the litter breakdown rate was explained by the hydrological, physico-chemical and physiographic components. Specifically, tidal range, salinity and sinuosity index are among the key factors in the most commonly used typological schemes for classifying transitional water ecosystems (i.e. Confinement Concept and Venice System), due to their influence on abundance and distribution of benthic macroinvertebrates and other guilds. 5. The patterns observed at the regional scale of the study suggest that certain key abiotic factors are likely to play a major role as drivers of plant detritus decomposition processes, through their influence on the overall metabolism of microorganisms and benthic macroinvertebrates. 6. These observations have implications for the identification of reference conditions for transitional water ecosystems in the studied area, on which all processes of classification and conservation of their ecological status are based.