To examine leaf litter breakdown and utilization by macroinvertebrates in estuarine intertidal flats located in the northwestern Seto Inland Sea, Japan, we investigated the breakdown rate of air-dried reed litter using a litter bag method at the study site. Approximately 70% of the initial weight remained one month after the field experiment, suggesting that most of the reed litter supplied from a river can remain for more than one month at the site. We investigated macroinvertebrate colonization in a litter bag with plural holes (d=3cm). Decapoda, Amphipoda, and Gastropoda species mainly colonized the litter bags during the year. To investigate the litter utilization by macroinvertebrates, we conducted a food supplementation experiment using air-dried litter and that exposed in the field for two weeks to allow colonization by microbes such as bacteria and microalgae (conditioned litter) in the laboratory. Conditioned litter supplied to Decapoda showed a remarkable decrease in both weight and area during one month, suggesting that some Decapoda species use reed litter as a food source.

Our field and laboratory experiment results suggest that reed litter supplied from a river has an important role as a food source and habitat for some macroinvertebrates in an intertidal estuary.