Breaking it down: leaf litter processing by invasive Chinese mitten crabs and associated effects on water quality in laboratory conditions

In freshwater streams, leaf litter decomposition is a crucial ecosystem function that provides energy and nutrients. Biological invasions by non-native decapods, like the common invasive Chinese mitten crab, could potentially alter decomposition rates and therefore affect this key ecosystem function. This experimental study sheds light on the detrivorous feeding behaviour of these crabs and its consequences for water quality, including dissolved nutrient concentrations, fine particulate organic matter and biological oxygen demand. Two different crab life stages were tested and compared to a control condition without crabs. The crabs were fed with leaf litter originating from five different trees, including alder, beech, Canadian poplar, willow and large-leaved linden. Our findings revealed that juvenile crabs had minimal impact on leaf litter breakdown and nutrient concentrations. In contrast, adult crabs significantly accelerated litter breakdown rates and substantially increased dissolved nitrogen concentrations in the water column. Both juvenile and adult crabs were found to enhance the amount of fine particulate organic matter and elevate biological oxygen demand. Considerable variations across different leaf litter diets were observed, demonstrating the impact of leaf litter characteristics on the feeding behaviour of Chinese mitten crabs. These results underscore the potential of Chinese mitten crabs to expedite leaf litter processing and nutrient release in freshwater ecosystems, highlighting the significant role that invasive species can play in altering ecosystem functioning.