The long-term effects of the tsunamis caused by the Great East Japan Earthquake on an intertidal host–parasite system

Due to the intimate relationship between hosts and parasites, parasites can be used as an indicator of host demography and provide a useful monitoring tool for conservation management. The tsunamis caused by the Great East Japan Earthquake damaged a large number of coastal organisms that host various parasite species. We monitored the demography of trematode parasites and their first intermediate host, the intertidal mud snail Batillaria attramentaria, between 2005 and 2024 to evaluate the impact of the tsunami on this snail-trematode system. We further investigated the changes in the community structure of potential second intermediate hosts (macrobenthic organisms) and definitive hosts (shorebirds) using the public database to evaluate their associations with trematode communities. Our long-term monitoring demonstrated that the trematode prevalence and diversity have fluctuated for more than 10 years after the tsunami event. The observed instability of parasite communities can be partially explained by the demographic imbalance of host populations and perhaps by other factors, including human activity, gradual land elevation and global climate change. Our study highlights the recovery process of coastal organisms from the tsunami disturbance and the potential usefulness of trematode parasites in monitoring their associated host communities. This article is part of the theme issue 'Managing infectious marine diseases in wild populations'.