Abstract
Monitoring of Tubuca arcuata in the Sumiyoshi tidal flat of Yoshinogawa Estuary, Tokushima Prefecture, has been conducted for five years through civic cooperation. This cooperative monitoring has clarified temporal change in the population density of Tubuca arcuata and in its distribution by particle size composition of the sediment. However, a questionnaire survey confirmed differences in awareness among citizens. Going forward, it will be necessary to conduct activities to raise satisfaction among participants, and to raise awareness to recruit participants.