Monitoring of intertidal fauna and flora on rocky shore and pier wall in southern Iwate

Representative Organization: Tohoku University

2015/04/01 - 2016/03/31
Once a year in Yoshihama bay, every three months at Okirai and Ofunato bays

Yoshihama bay, Okirai bay, Ofunato bay

Field survey

We examine fauna and flora of the intertidal organisms in a rocky shore and pier walls to estimate the impact of the 2011 disaster and monitor the recovery process from it by video camera in case for vertical pier wall at Okirai and Ofunato Bay.

1. Fauna and flora of intertidal zone before and after the Great East Japan Earthquake Fauna and flora of intertidal zone have been surveyed at Funasaku rocky shore in Yoshihama Bay. Before the 3.11 Earthquake, 38 macro algae were common at three stations in average in the north-west rocky beach. After the event, 14, 17, 23 and 20 species have been observed annually in subsided area in 2012, 2013, 2014 and 2015 respectively. On the other hand, 25 invertebrates were common in the intertidal zone at the south-east rocky shore before the earthquake. After the event, 22, 20, 20 and 24 species have been observed annually in 2012, 2013, 2014 and 2015, respectively (Fig.1). Fig.1 Changes of fauna and flora in intertidal zone at Funasaku rocky shore in Yoshihama Bay before and after the Great East Japan Earthquake. No. of species Before after 2001-2005 2012 2013 2014 2015 Flora (*1 38 14 17 23 20 Fauna (*2 25 22 20 20 24 *1: average number of macro algal species among three station *2: total number of invertebrate species appeared at four stations. 2. Intertidal community on the wall of breakwaters Succession processes on the breakwaters have changed depending on the survey site. At closed and low exposed site as Kamihira in Ofunato Bay which had been low biodiversity before the earth quake but high biomass and dominated by the alien barnacle Balanus glandula, the biodiversity has become increased as a result of recruitments of Semibalanus cariosus and Chthamalus challengeri more in three years after the earthquake. And the situation has not changed afterward, although B. glandula is still a dominant species in the community. On the other hand, at semi-closed and high exposed site as Sakihama in Okirai Bay which had low biomass and low biodiversity before the earthquake. However, due to decreased sea urchin density just after the backwash of the tsunami, biodiversity have become high by recruitments of the thatched barnacle, Semibalanus cariosus and then mussels, Mytilus galloprovincialis in the intertidal zone. As a result of the increment of the two dominant sessile animals, other organisms such as macroalgae and other barnacles settled on them and the biodiversity became increased. However, gradual increase of the sea urchin density year by year caused decrement of sessile organisms and the intertidal community almost disappeared in late 2015, except alien barnacle, Perforatus perforates which is firstly found at Otsuchi Bay and Okirai Bay in 2012 at the Pacific side of Japan and is increasing its density at the low intertidal zone. 3. Distribution and ecological features of P. perforatus in Japan Distribution of the alien barnacle P. perforatus has been surveyed along the northern shore of Honshu island and northern shore of Hokkaido in Japan. As a result, southern limit of P. perforatus was has found Uwozu in Toyama Prefecture at the Japan Sea side, northern limit was Kan-onji fishing port near Esashi in Hokkaido. On the other hand, southern limit at the Pacific side was Shizuhama fishing port in Miyagi Prefecture. No specimen has found at the Pacific side in Aomori Prefecture. Considering the present distribution, gradual expansion to the coast of Iwate Prefecture by natural dispersion of their planktonic larvae was not suggested, instead anthropogenic activities such as a barge and its tugboats may act vectors of this species from the Japan Sea side to the damaged ports by the tsunami at the Pacific side through the Tsugaru Strait. Settlement season of P. perforatus has been investigated at Sakihama, Iwate Prefecture and Funakawa, Akita Prefecture by using PVC test panels set at the low intertidal zone. Settlements were recorded during sea temperature raised more than 13-15 degree C. Settlement seasons were May to November (2013-14) at Funakawa, August to September (2012), July to August (2013) and July to October (2014), and June to October (2015) at Sakihama.Settlement season is expanding longer year by year at Okirai Bay. Size distribution of the barnacle shell had been investigated from June, 2013 to November, 2014 at Sakihama and Namiita in Okirai Bay. P. perforates grew 9-11mm (shell diameter) during a year after its settlement, and reached 14mm at the following a year. It was very rare to have more than 20mm in shell size at the two stations. Rearing experiments had carried out to know its larval growth and the survival against seawater temperatures and salinities. Nauplii metamorphosed to cyprids at more than 15 degree C in temperature and more than 20 in Salinity with more than 50 % of survival rate. Interim evaluation Intertidal community at the rocky shore in Yoshihama Bay has still on the way to recovery to the state before the earthquake in case of its flora, but almost restored on its fauna. While, successions of intertidal communities on the wall of breakwaters have changed much depending on the exchange rate of a bay water. Intertidal community at Ofunato Bay which has a closed bay has not changed much before and after the Earth Quake, although several species recruited a little to inside the bay by the breakdown of the tsunami guard at the bay mouth and attributing increment of exchange rate of the seawater. A new tsunami guard will be completed in 2016, it need to monitor the community to know the influence to species composition to them. At Sakihama break waters which had drastic change of the community, we have learned the influence by the sea urchin (and carnivorous gastropods) to the community structure and biodiversity. An alien barnacle, Perforatus perforatus will be a symbolic species to introduce just after the earth quake and have survived at the Pacific side with increasing its density. We have to monitor its density and distribution to know the influence to native community.

FY2015 Monitoring of intertidal fauna and flora on rocky shore and pier wall in southern Iwate

CTD Ofunato (Kamihira & Shizu) 1504-1512