Changes in fish community in seagrass beds in Mangoku-ura Bay from 2009 to 2014, the period before and after the tsunami following the 2011 off the Pacific coast of Tohoku earthquake

Abstract

In order to evaluate the impact of the tsunami following the 2011 off the Pacific coast of Tohoku earthquake on habitat condition and fish community structure in seagrass Zostera marina beds, seagrass vegetation and structure of fish communities were investigated in Mangoku-ura Bay, on the Pacific coast of northern Japan, from 2009 to 2014. Underwater observation revealed a decrease in the vegetation coverage in the seagrass bed after the tsunami. A total of 1764 fishes belonging to 37 species (18 families) were collected. Effects of year on mean fish abundance (no. fish 100 m−2) and biomass (fish weigh in g 100 m−2) in the seagrass bed were significant, while there was no significant effect of year on number of fish species. Seagrass-associated or substrate-associated species such as Sebastes cheni and Ditrema viride were dominant by weight in the fish community in 2009, and were replaced with sand or mud bottom-associated fish species such as Acanthogobius flavimanus in 2011. An increase in abundance of sand or mud bottom-associated fish species such as Acentrogobius virgatulus and Takifugu niphobles contributed to significant increase in the mean fish abundance in 2011, when seagrass shoot density decreased due to the disturbance of the sea bottom and sediment deposition by the tsunami. Changes in sea bottom and vegetation conditions are concluded to have been factors causing the change in dominant fish species.