Impact of huge tsunami in March 2011 on seaweed bed distributions in Shizugawa Bay, Sanriku Coast, revealed by remote sensing

Shingo X. Sakamoto; Shuji Sasa; Shuhei Sawayama; Ryo Tsujimoto; Genki Terauchi; Hiroshi Yagi; Teruhisa Komatsu

doi:10.1117/12.999308

11 December 2012 Impact of huge tsunami in March 2011 on seaweed bed distributions in Shizugawa Bay, Sanriku Coast, revealed by remote sensing

Shingo X. Sakamoto, Shuji Sasa, Shuhei Sawayama, Ryo Tsujimoto, Genki Terauchi, Hiroshi Yagi, Teruhisa Komatsu

Author Affiliations +

Proceedings Volume 8525, Remote Sensing of the Marine Environment II; 85251B (2012) https://doi.org/10.1117/12.999308
Event: SPIE Asia-Pacific Remote Sensing, 2012, Kyoto, Japan

Abstract

Seaweed beds are very important for abalones and sea urchins as a habitat. In Sanriku Coast, these animals are target species of coastal fisheries. The huge tsunami hit Sanriku Coast facing Pacific Ocean on 11 March 2011. It is needed for fishermen to know present situation of seaweed beds and understand damages of the huge tsunami on natural environments to recover coastal fisheries. We selected Shizugawa Bay as a study site because abalone catch of Shizugawa Bay occupied the first position in Sanriku Coast. To evaluate impact of tsunami on seaweed beds, we compared high spatial resolution satellite image of Shizugawa Bay before the tsunami with that after the tsunami by remote sensing with ground surveys to know impact of the tsunami on seaweed beds. We used two multi-band imageries of commercial high-resolution satellite, Geoeye-1, which were taken on 4 November 2009 before the tsunami and on 22 February 2012 after the tsunami. Although divers observed the tsunami damaged a very small part of Eisenia bicyclis distributions on rock substrates at the bay head, it was not observed clearly by satellite image analysis. On the other hand, we found increase in seaweed beds after the tsunami from the image analysis. The tsunami broke concrete breakwaters, entrained a large amount of rocks and pebble from land to the sea, and disseminated them in the bay. Thus, hard substrates suitable for attachment of seaweeds were increased. Ground surveys revealed that seaweeds consisting of E. bicyclis, Sargassum and Laminaria species grew on these hard substrates on the sandy bottom.

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Shingo X. Sakamoto, Shuji Sasa, Shuhei Sawayama, Ryo Tsujimoto, Genki Terauchi, Hiroshi Yagi, and Teruhisa Komatsu "Impact of huge tsunami in March 2011 on seaweed bed distributions in Shizugawa Bay, Sanriku Coast, revealed by remote sensing", Proc. SPIE 8525, Remote Sensing of the Marine Environment II, 85251B (11 December 2012); https://doi.org/10.1117/12.999308

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