Field survey of rocky shore ecosystem in Oshika Peninsula

Representative Organization: Tohoku University

2015/04/01 - 2016/03/31
monthly

Kitsunezaki beach, Oshika Peninsula
0178_R01.pdf

Field survey

Dynamics of population or community after the subsidence will be monitored at area B in rocky shore of Oshika Peninsula. In area B, survival and growth of Eisenia bicyclis (brown algae) and hervivorous gastropod, Omphalius rusticus will be monitored, and their population dynamics after subsidence will be clarified in relation to various environmental factors.To clarify the effect of O. rusticus on E. bicyclis, exclosure experiment of O. rusticus will also be conducted.

1) Dynamics of Eisenia bicyclis community Spatio-temporal dynamics of the Eisenia bicyclis community in a permanent survey area of 120 m2 on the coast of Kitsune-Zaki have been monitored since July 2011. The 0.9 m-subsidence occurred by the 2011 earthquake caused the abundant settlement of young plants to the shallower area. At the deeper area, settlement of young plants was rare and over 60% of adult plants went through the earthquake survived and aged over eight years old. Breakwater restoration started from 2014 destroyed and landfilled the shallower 24 m2 area of the Eisenia community. Loss of the young individuals at shallower area and few supplies of young plants to the deeper area will cause the diminishing of the kelp community in the near future. 2) Analysis of the genetic structure of the Eisenia bicyclis community Leaf samples of all individuals of Eisenia bicyclis in the permanent survey area were obtained in July 2011, April 2012 and July 2014. We succeeded in the extraction of purified DNA from the samples and in the trial of the analysis of genetic structure of the kelp community. 3) Life history analysis of Omphalius rusticus Based on the periodical sampling survey and the mark-recapture survey, life history characteristics of Omphalius rusticus was analysed. Young snails recruited in September grew quickly and joined reproduction at age two. Growth lowered from age three and the maximum longevity was estimated as over four years old. Seasonal changes of the recapture rate showed the high mobility of the snails in spring and summer. 4) Estimation of the grazing pressure of Omphalius rusticus Snail exclusion experiments sustained for nine months showed that the grazing activity of the snails disturbed the early settlement of young algae. Continuous removal of depositing mud by the snails, however, facilitated the growth of the algae survived the early grazing pressure by snails. The grazing activity of Omphalius rusticus, the densely distributed small snail, is not negligible in this kelp bed community.

FY2015 Field survey of rocky shore ecosystem in Oshika Peninsula