Rocky Intertidal Zonation: Impacts and Recovery from the Great East Japan Earthquake

Abstract

We assessed the course and status of the recovery of rocky intertidal zonation after the Great East Japan Earthquake by conducting a census of the vertical distribution of 11 dominant macrobenthos (7 sessile and 4 mobile species) around the mid-tidal elevation at 23 sites along the Sanriku Coast, 150–160 km north-northwest of the epicenter of the earthquake. Sites were observed from 2011 to 2013, and the vertical distributions of each species were compared with those from the pre-earthquake period. Our results show that the earthquake considerably altered rocky intertidal zonation, mainly through coseismic subsidence rather than by the subsequent tsunami. By 28 months after the earthquake, the zonation of late-successional sessile taxa had not recovered, suggesting that the rocky intertidal community will experience a long delay before recovering from the influence of the earthquake. The dynamics of rocky intertidal zonation after the earthquake and accompanying subsidence includes two unique features: a delayed negative impact and an occasional increase in population sizes of several taxa. Neither of which has been reported following earthquakes of similar magnitude with accompanying uplift, in which there were mass mortalities of zone-forming species within 1 year after the event, preceding downward shifts in their zonations.