Temporal changes of the fish community in seagrass beds in Funakoshi and Otsuchi bays after habitat destruction caused by a tsunami in 2011

The temporal changes in the fish community structure before and after a tsunami in 2011 were investigated in Funakoshi and Otsuchi bays, Iwate prefecture, on the Pacific coast of northern Japan. Fish species richness, abundance, biomass, and species composition were analyzed in relation to temporal variability of biotic and abiotic environmental conditions in two sub-intertidal seagrass Zostera marina beds. Mean seagrass shoot density decreased to < 5.8% of its original density after the tsunami, and gradually increased during the following survey periods in both bays. A total of 5206 fishes (74 taxa, 36 families) were collected by quantitative sampling for 10 years from 2009 to 2018. The Embiotocidae fishes dominated in terms of biomass in both bays. Mean seagrass shoot density had the most significant positive effect on total fish biomass in Funakoshi Bay. Fish species richness decreased immediately after the tsunami in both bays, corresponding to the drastic decrease in seagrass shoot density. Thereafter, the species richness gradually increased during the post-disturbance period of 7 years. In summer 2017, after approximately 6 years since the tsunami occurred, the seagrass habitat had recovered, and the fish community became similar to that before the tsunami disturbance in both bays.