Comparison of fish assemblage structures among microhabitats in a salt marsh in Lake Hinuma, eastern Japan

A total of 33 fish species, including commercially important and threatened species, were collected in three microhabitats (upper and lower areas of a small creek, and a marsh edge separate from the creek) of a salt marsh in Lake Hinuma, eastern Japan, in October 2014, and January, April and July 2015. Five species (Acanthogobius lactipes, Oryzias latipes, Mugil cephalus cephalus, Tribolodon brandtii and Salangichthys microdon) were dominant and accounted for 90.7% of the total number of individuals. The fish assemblage structures differed remarkably among the microhabitats, tending toward higher species and individual numbers on the marsh edge than in the upper creek. Species compositions also differed between the upper creek and the other microhabitats. Food availability (e.g., mysids, chironomid larvae and detritus) was considered to be a causative factor of the assemblage structure differences. In addition, microhabitat variations in water depth, dissolved oxygen level and bottom sediment, the upper creek being shallower with lower dissolved oxygen and higher sediment silt-clay proportion compared with the marsh edge, were also causative factors that indicated the importance of both biotic and abiotic environmental factors in the determination of fish distribution patterns across salt marsh microhabitats.