engleski

The impact of invasive amphipod Dikerogammarus villosus on leaf litter decomposition in Croatian and German rivers

Native amphipod shredders are crucial for leaf litter decomposition. Invasive amphipods, like Dikerogammarus villosus, are replacing native shredders potentially affecting the processing of allochthonous organic matter in aquatic ecosystems. This study investigated differences in in-situ leaf litter decomposition between sites with and without the invasive D. villosus. The experiment was conducted at six locations, two locations in Germany and four in Croatia ; two sites were compared at each location, upstream with native species and downstream where D. villosus was present. At each site, coarse and fine leaf bags containing 2.5 g of willow leaves were placed in the water. Leaf bags were sampled three times, macroinvertebrates were identified and measured after each sampling, and leaves were dried at 60 °C for 16 hours. At all locations two- factorial PERMANOVA indicated that shredder community differed significantly between upstream and downstream sites, due to the presence of D. villosus. Leaf litter decomposition rates were 0.7-7.7 times lower in fine bags. Decomposition rates in coarse bags showed opposite results: three of six upstream sites with abundant native Gammarus species had significantly higher rates, while three of six downstream sites, where D. villosus was dominant shredder, also had higher rates. Locations with higher decomposition rates at downstream sites had higher water temperatures. These results suggest that replacement of the functional role of native Gammarus shredders by the invasive D. villosus depends on water temperature and shredder community composition in invaded rivers.

amphipoda ; leaf litter decomposition ; invasive species

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