The Ecosystems Monitoring Survey of the Pacific Coastal Areas of the Tohoku Region in FY2013

Summary

### 1. Purpose of the project

The earthquake and ensuing tsunami that occurred on March 11, 2011 off the Pacific coast of Japan’s Tohoku region (hereinafter “the Great East Japan Earthquake” or “the disaster”) had an enormous impact on the natural environment, people’s lives, and the social environment in the Pacific coast of the Tohoku region and elsewhere. The purpose of this project was to survey tidal flats, seagrass beds, seaweed beds, and seabird breeding grounds in the coastal areas of the Tohoku region—where the impact of the Great East Japan Earthquake on the natural environment was particularly apparent—and to gauge the effects of the earthquake and tsunami on the natural environment in the region.

### 2. Results of the project

## (1) Survey of tidal flats

For the tidal flats, the numbers of and presence of benthic organisms were recorded through quantitative and qualitative surveys at eight sites (Tsugaruishi River, Orikasa River, Unosumai, Otomoura, Mangokuura, Matsushima Bay, Idoura, and Torinoumi). The results of the survey of each of the sites showed that at some of the sites, species present before the disaster still could not be confirmed. Nevertheless, on the whole, the tidal flat environment had become more stable than it had been immediately after the disaster, and the number of species occurring at the tidal flats at each of the sites had increased and were recovering, although individual densities were low. Moreover, because fluctuations were observed in the compositions of dominant species compared to pre-disaster compositions, it is necessary to continue to survey the changes that are occurring, including changes to the benthic fauna.

## (2) Survey of seagrass beds

For the seagrass beds, survey points were decided upon near and off the shore at each of the sites (Yamada Bay, Hirota Bay, Mangokuura, and Matsushima Bay). Species of seagrass occurring in quadrats and their respective coverage were recorded. Compared to the results of the $ 7^{th} $ National Survey on the Natural Environment (seaweed bed survey), seagrass showed an overall decline, with a low seagrass density at the survey sites. Nevertheless, seagrass exhibited signs of recovery, although slight. One of the reasons that it is necessary to conduct continual surveys is to keep track of this recovery.

## (3) Survey of seaweed beds

For the seaweed beds, species occurring in quadrats and their respective coverage were recorded at Yamada Bay, Onagawa Bay, the coastal part of Kitaibaraki City, and the coastal part of Nakaminato. At each of the sites, there was a decline compared to pre-disaster levels, although on the whole, seaweed communities overall were recovering. Nevertheless, because there is a possibility that seaweed communities could change depending on the conditions of the survey sites and the surrounding environments, it is necessary to continue to monitor.

## (4) Survey of seabirds

In the seabird survey, on the islands of Kabushima, Sanganjima, and Ashijima, the number of nests was estimated from the nesting areas and nest densities. The direct impact of the disaster could not be determined from the survey of the sites, but at each of the sites soil runoff, changes in vegetation, etc. were observed. There is a possibility that soil runoff, changes to vegetation, etc. could hinder the breeding of seabirds. It is therefore necessary to conduct ongoing surveys of their habitats and other such factors.