Field survey of rocky shore ecosystem in Oshika Peninsula

Representative Organization: Tohoku University

2013/04/01 - 2014/03/31
monthly

Kitsunezaki coast, Oshika Peninsula

Field survey

Dynamics of population or community after the subsidence was monitored at two areas (areaA and B) in rocky shore of Oshika Peninsula. In area A, distribution pattern of Sargassum yezoense (a species of brown algae) and two species of sea urchins: Mecocentrotus nudus and Hemicentrotus puicherrimus was examined, and interaction among these species was discussed with relation to subsidence and water temperature. In area B, survival and growth of Eisenia bicyclis (brown algae) and hervivorous gastropod, Omphalius rusticus were monitored, and their population dynamics after subsidence were clarified in relation to various environmental factors.

0029_R01_map01.pdf, 0029_R01_map02.pdf

(1) area A In this area, population dynamics of Sargassum yezoense and sea urchins have been monitored since before the tsumani and subsidence occurred. Sea urchin Mesocentrotus nudus, which had been abundant in the site A and B, was not or rarely found after tsunami, and this continued during 2013 survey. They might have been run off by tsunami and could not recover possibly because of unfavorable high water temperature in summer of 2012. In site A, size (distance between upper and lower limit) of the Sargussum yezoense bed began expanding in August 2011. In October 2012 its size reached 6 m and then have been maintained by August 2013. This expanding of Surgassum bed may be related to the decline of sea urchins, which feed on the macroalgae. Those monitoring will be continued next year. (2) area B In this area, population dynamics of Eisenia bicyclis have been monitored soon after the tsunami and subsidence occured. Eisenia recruitment peaks were observed twice: in August-October 2011 and May-July 2013. Recruitment rarely occurred in the deeper zone which had been gone below the lower limit of Eisenia distribution. In this zone, growth rate was also lower and Eisenia may possibly extinct at some future date. Eisenia monitoring will be continued next year. Herbivorous snails Omphalius rusticus was found across the study area and Chlorostoma lischkei was found in the shallower zone. As its grazing may possibly influence Eisenia survival and growth, exclusion and/or inclusion experiment will be conducted.

FY2013 Field survey of rocky shore ecosystem in Oshika Peninshura

CTD Oshika Peninsula (area B) 1304-1403