Mitsuyo Saito

Coastal habitats are crucial for supporting ecological processes and serve as vital ecosystems for diverse fish species, providing essential functions such as feeding, nursery provision, and reproductive habitats. Fish communities are ecologically important components of coastal ecosystems and are affected by multiple environmental factors. Despite their importance, determining the effects of environmental factors on seasonal variations in fish species diversity and community dynamics remains a challenge. The advent of environmental DNA (eDNA) technology, an environmentally conscious approach, has resulted in considerable advancements in recent years and has been progressively adopted for marine fish population monitoring. Here, we used environmental DNA metabarcoding to study seasonal variations in fish community structure on a coastal island, and we assessed the effects of environmental factors in structuring these communities. Our findings revealed a rich diversity of 72 fish species across 40 families and 23 orders in the seawater surrounding an island of the Seto Inland Sea (SIS), Western Japan. Notably, the composition of fish communities varied significantly between seasons, with seawater temperature, salinity, and dissolved inorganic phosphorus (DIP) concentration identified as important factors correlated with fish communities’ structures. In conclusion, our study provides useful information of fish diversity, and we suggest that eDNA is a valuable technique for monitoring fish diversity in coastal areas. These findings are crucial for ecological studies and the environmental monitoring of oceanic coastal environments.