1. IntroductionMatsukawa-ura Lagoon, a shallow brackish la-

goon located in northeastern Fukushima prefec-ture, communicates with the Pacific Ocean at thenorthern entrance of the lagoon（Fig. 1）. Matsu-

kawa-ura Lagoon has a 23Ȃkm circumferenceand surface area of 5.9 km2. Before the 2011 offthe Pacific coast of Tohoku Earthquake（herein-after, the earthquake）, approximately 70% of thesurface area（5. 9 km2）was dry at low tide,forming a tidal flat（GEOSPATIAL INFORMATION

AUTHORITY OF JAPAN, 2011）. Actually, Matsuka-wa-ura Lagoon is a major fishing ground forManila clams（SATO et al., 2007）. During 1910Ȃ1970, artificial seeding of the edible red alga Por-phyra tenera, made the area a major fishery thatsupplied other “nori” seaweed production areasthroughout Japan（IWASAKI and MATSUDAIRA,1954）. Because of environmental changes occur-ring from 1971 spurred by waterway dredging

La mer 56 : 11Ȃ20, 2018Société franco-japonaise dʼocéanographie, Tokyo

Temporal change of eelgrass Zostera marina bed inMatsukawa-ura Lagoon, Fukushima Prefecture

Akira MATSUMOTO1)＊, Kaoru NARITA1), Tsuneo FUJITA1),Tatsuma SATO2), Ikuo MATSUMOTO2) and Toshihiro WADA3)

Abstract: This study estimated the area of eelgrass beds in Matsukawa-ura Lagoon and investi-gated spatiotemporal changes of the area using satellite images obtained after the 2011 off thePacific coast of Tohoku Earthquake. Furthermore, we examined the spatial distribution of mudcontents in the lagoon after the earthquake. In April 2012, the eelgrass beds were observed insmall area（0.013 km2）of the northern part of the lagoon. Almost all eelgrass was physically re-moved by devastating tsunami waves. In September 2014, the bed area had increased sharply toapproximately 0.39 km2. The spatial distribution also expanded from the northern to the centrallagoon. In November 2015, the rate of increase was only approximately 10% compared with theprevious year. No remarkable change was found in the spatial distribution. The mud contentwas 0Ȃ79%, the eelgrass bed was observed in the area where the mud contents were less than30%. The eelgrass bed area in 2015 was roughly twice that in 2010. Eelgrass beds had expandedto the upper edge of the waterway after the earthquake. The subtidal zone, which is suitable foreelgrass growth, expanded because of ground subsidence.

Keywords : Matsukawa-ura Lagoon, Zostera marina, Tsunami, Subsidence

1）Fukushima Prefectural Fisheries ExperimentalStation Soma Branch, Soma, Fukushima 976Ȃ0022,Japan

2）Fukushima Prefectural Inland Water FisheriesExperimental Station, Inawashiro, Fukushima969Ȃ3283, Japan

3）Institute of Environmental Radioactivity, Fukush-ima University, Fukushima 960Ȃ1296, Japan

＊Corresponding author:E-mail: mattun_s15@yahoo.co.jp

1）Institute of Marine Science, Burapha University,Bangsaen, Chon Buri 20131, Thailand

2）Department of Aquatic Science, Faculty of Sci-ence, Burapha University, Bangsaen, Chon Buri20131, Thailand

3）Atmosphere and Ocean Research Institute, The

University of Tokyo, 5Ȃ1Ȃ5, Kashiwanoha, Kashi-wa, Chiba 277Ȃ8564, Japan

＊Corresponding author: Thidarat NoiraksarTel: + 66(0)38 391671Fax: + 66(0)38 391674E-mail: sargassum2005@gmail.com

12 La mer 56, 2018

operations from the entrance to the inside of thelagoon（YANAI and OWADA, 1976）, Matsukawa-ura fishery changed from artificial seeding ofPorphyra tenera to Monostroma nitidum culture

（ONO et al., 1972）. In the northeastern partof the lagoon, the eelgrass bed was formedbefore the earthquake（GEOSPATIAL INFORMATION

AUTHORITY OF JAPAN, 2011）. The eelgrass Zosteramarina stretches its rhizomes and roots to thesandy bottom. The leaf length reaches 1 m ormore. These rhizomes or roots of the eelgrasshave sometimes disturbed the Manila clam fish-ery. Therefore, the excess eelgrass near the fish-ing ground was sometimes thinned out by fisher-man before the earthquake. Nevertheless, theeelgrass bed generally plays important ecologi-cal roles by attaching diatoms as a primary pro-ducer to their leaves（DUFFY et al., 2015）. It iswidely known to be a nursery ground for vari-ous juvenile fish including commercial fish spe-

cies（e.g., KIKUCHI and PERES, 1977）. In addition, inrecent years, growth-inhibiting bacteria havebeen found from eelgrass possessing strong ac-tivity against the toxic dinoflagellate Alexandri-um tamarense and red tide raphidophytes Chat-tonella antiqua and Heterosigma akashiwo（ONISHI

et al., 2014; IMAI et al., 2016）. The earthquakeʼ sconsequent tsunami temporarily removed manyeelgrass beds from Miyako Bay, Iwate Prefec-ture and Matsushima Bay, Miyagi Prefecture,not only Matsukawa-ura Lagoon（SAKAMAKI andNISHIMURA, 2014; SAKAMAKI et al., 2016; OKADA andFURUKAWA, 2013; SASA et al., 2012; KOMATSU et al.,2015）. After the tsunami, recovery trends wereobserved for some eelgrass beds（SASAKI et al.,2016; MURAOKA et al., 2016）. As in these eelgrassbeds, the recovery trend was also apparent inthe Matsukawa-ura Lagoon. In fact, the recoveryreportedly interfered with the Matsukawa-urafishery. Considering the fishery and ecosystem

Fig. 1 Map of the study area in Matsukawa-ura Lagoon, Fukushima Prefecture:a）Map of Tohoku, Japan; and b）Map of Matsukawa-ura Lagoon, Fukushima Prefecture and60 stations of sediment sampling. *Sand-covered during 2012Ȃ2013.

13Temporal change of eelgrass Zostera marina in Matsukawa-ura Lagoon

comprehensively, the eelgrass bed in Matsuka-wa-ura Lagoon might exert a particularly usefulfunction. Nevertheless, no report describes astudy showing the spatial distribution of eelgrassbeds in the lagoon after the tsunami. Examina-tion of the spatiotemporal changes of eelgrassbeds after the tsunami must therefore be con-ducted. As described herein, we estimated theeelgrass bed area and examined spatiotemporalchanges of the lagoon area using Google Earthsatellite images obtained after the earthquake.Furthermore, we investigated factors determin-ing the distribution of eelgrass beds in the la-goon.

2. Materials and methodsEstimation of area of eelgrass beds using satel-lite imagery

For this study, we used Google Earth satelliteimages showing Matsukawa-ura Lagoon taken inApril 2012, September 2014, and November 2015.We used Google Earth Pro（Ver. 7.1.5.1557）toidentify eelgrass Zostera marina based on thecolor tone of the imagery. Matsukawa-ura La-goon was shallow（approximately 1.5 m）enoughthat the edge of eelgrass bed（black）could bedistinguished from sandy bottom（light brown）as well as Waquoit Bay, Massachusetts（SHORT

and BURDICK, 1996）. The outer edge of the identi-fied eelgrass was traced to ascertain its exactlatitude and longitude. Each eelgrass area wasestimated to 0.1 m2 based on the latitude and lon-gitude using R statistical software（Ver. 3.3.2, RDEVELOPMENT CORE TEAM, 2016）and a geospheresoftware package（ver 1.5Ȃ5, HIJMANS, 2016）. Theareas（km2）of all eelgrass beds were found ev-ery year. In addition, we examined the temporalchange of the spatial distribution of the eelgrassbed. Furthermore, we estimated the area of eel-grass bed before the earthquake using GIS dataobtained from the acoustic and aircraft surveys

conducted in 2010（GEOSPATIAL INFORMATION

AUTHORITY OF JAPAN, 2011）. Thereby, we wereable to compare eelgrass areas before and afterthe earthquake.

Sediment sampling and determination of mudcontent

Using an Ekman-Birge sampler, we collectedsurface sediment samples（approximately 3 cm）from 60 sites around Matsukawa-ura Lagoon inJuly every year from 2012 through 2015(Fig. 1b). The particle-size distribution of sedi-ments was measured using laser diffraction/scattering particle-size analyzers（SALDȂ3100;Shimadzu Corp.）. The mud content was calculat-ed from the percentage of the particle size lessthan 0. 063 mm in the particle-size distribution.The spatial distribution of mud contents was ex-amined using spline interpolation using statisti-cal software R（Ver. 3.3.2, R DEVELOPMENT CORE

TEAM, 2016）and the akima package（ver 0.6Ȃ2,AKIMA and GEBHARDT, 2016）. The relation be-tween the spatial distribution of mud contentand that of eelgrass was investigated. Further-more, we compared the spatial distribution ofmud contents in our sediment samples after theearthquake and that of distribution surveyed in2010（GEOSPATIAL INFORMATION AUTHORITY OF

JAPAN, 2011）.

3. Results and discussionSpatiotemporal distribution of eelgrass bed andmud contents

In April 2012, the eelgrass bed was found inthe northern part of the Matsukawa-ura Lagoon.Its area was as small as 0.013 km2（Fig. 2a）. Ap-proximately two years later in September 2014,the area had increased sharply by approximate-ly 30 times（0.39 km2）. The spatial distributionalso expanded from the northern part to the cen-ter of the lagoon（Fig. 2b）. In November 2015,

14 La mer 56, 2018

the increase of the area was only approximately10% compared with that of the previous year. Noremarkable change was found in the spatial dis-tribution（Fig. 2c）. In the lagoon as well as othercoastal areas（personal communication）, the leaflength and shoot density of eelgrass were high-est in summer and lowest in winter. Moreover,other types of seaweed grow in winter. There-fore, to minimize underestimation and overesti-mation, we specifically examined September andNovember（2014 and 2015, respectively）in thisstudy, when the eelgrass grew and when no oth-er algae were observed. The eelgrass bed areabefore the earthquake was estimated as approxi-mately 0.22 km2 from the survey conducted byGeospatial Information Authority of Japan in2010. The area after the earthquake（in 2012）was estimated as approximately 0.013 km2,which was remarkably lower than the area be-fore the earthquake. The devastating tsunamifollowing the earthquake destroyed the sandbarfacing the Pacific Ocean in the eastern part ofthe lagoon（NISHI et al., 2012）. From the eelgrassarea in April 2012, almost all eelgrass beds hadbeen physically removed by the devastating tsu-

nami. Some effects such as construction activitymight have been used to restore the sandbar. Inother coastal areas, it had been reported thatmuch of the eelgrass beds had been removedfrom the bottom by tsunami wave action

（WHANPETCH et al., 2010; MURAOKA et al., 2016;NAKAOKA et al., 2017）. Although it was suggestedthat almost all the eelgrass plants in Matsuka-wa-ura Lagoon had been removed from the bot-tom by the tsunami, a few eelgrass plants had re-mained in the northern part of the lagoon in 2012

（Fig. 2a）. The little remaining eelgrass was alsoobserved visually in another study（ABE et al.,2017）. In that study, the area of eelgrass bed re-portedly expanded to roughly twice its area of2010 during the subsequent three years. In addi-tion, the northern and central part of the lagooninto which the eelgrass bed had expanded aremajor fishing grounds for Manila clams（SATO etal., 2007）. Therefore, some concern arose thatthe rhizomes or roots of the eelgrass might dis-turb the Manila clam fishery. However, ABE et al.

（2017）reported that the little remaining eel-grass might serve as refuges for the clams be-cause of their function as a natural barrier resist-

Fig. 2 Spatiotemporal change of eelgrass bed（km2）in Matsukawa-ura Lagoon during 2012Ȃ2015:a）April 2012, b）Sep. 2014, and c）Nov. 2015.

15Temporal change of eelgrass Zostera marina in Matsukawa-ura Lagoon

ing the tsunami waves. Therefore, the possibilityexists that the eelgrass was beneficial for the re-covery of clams and the entire ecosystem in thelagoon after the tsunami. Although eelgrass bedsin other prefectures that had reportedly disap-peared because of the tsunami had also startedto recover（MURAOKA et al., 2016）, no report ofany other study describes eelgrass beds that had

increased beyond the pre-tsunami area.The spatial distribution and the temporal

change of mud contents are depicted in Fig. 3. InJuly 2012, the mud content was low（0Ȃ17.1%）inthe northern and the central parts of the lagoon.However, the mud contents were high（76.4%）in the southern area of the lagoon（Fig. 3a）.During 2014Ȃ2015, the spatial distribution of high

Fig. 3 Temporal change of spatial distribution of mud content（%）in Matsuka-wa-ura Lagoon during 2012Ȃ2015 and sediment distribution in 2010:a）July 2012, b）July 2014, c）July 2015, and d）2010.

16 La mer 56, 2018

mud contents was shifted from the south to thewest of the lagoon（Figs. 3b, 3c）. In 2015, maxi-mum mud contents（79. 0%）were observed inthe western part of the lagoon（Fig. 3c）. Lowmud contents（less than 30%）were observed inthe central part of the lagoon in all years. Com-parison showed that the spatial distribution ofhigh and low mud contents in the south andwest of the lagoon in 2012 differed from that in2010（Figs. 3a and 3d, GEOSPATIAL INFORMATION

AUTHORITY OF JAPAN, 2011）. Nevertheless, noclear difference was apparent between the spa-tial distribution, which was high in the westernlagoon in 2015 and that in 2010（Figs. 3c and 3d,GEOSPATIAL INFORMATION AUTHORITY OF JAPAN,2011）: The high and low mud contents observedin the southern and western areas of the lagoonin 2012 might be attributable to the tsunami. Af-ter the tsunami, the supply of particles of differ-ent particle sizes from Koizumi-gawa River, Uda-gawa River, and Ume-kawa River（ARITA et al.,2014）suggest that the spatial distribution ofmud contents might have returned to the statethat prevailed in 2010, before the tsunami.

Factors controlling the eelgrass bed distribu-tion

Comparison between the eelgrass bed distri-bution in 2015（Fig. 2c）and that of mud con-tents the same year（Fig. 3c）shows that theeelgrass bed was observed in the northern andcentral parts of the lagoon, where the mud con-tents were less than 30%. Four important factorscontrol eelgrass growth（Table 1）. Generally,previous reports demonstrate that mud contentsof less than 30% are suitable for eelgrass bed for-mation（Table 1, FISHERIES AGENCY OF JAPAN andMARINO-FORUM 21, 2007）. Therefore, the currentdistribution of the eelgrass bed in the lagoon wasapparently also regulated by mud contents inour study. As described in the previous section,

although the spatial distribution of mud contentshad reverted to that in 2010（Fig. 3d）, the eel-grass bed area had expanded to roughly twicethat of 2010 in the following three years（Figs. 2,4）. In other words, the spatial distribution of theeelgrass bed before the earthquake would beregulated by some factor different from the mudcontents. The change in the spatial distributionof eelgrass bed after the earthquake is portrayedin Fig. 4. Apparently, the eelgrass bed after theearthquake had expanded to shallow areas suchas the upper edge of waterway which dried outat low tide before the earthquake, with no ex-pansion to the center of the waterway（Figs. 4band 4d）. YANAI and OWADA（1976）observedbottom water velocity with consideration of thewaterway topography. Reportedly, the water ve-locity increased from the shallow area（upperedge）to the deepest area（center）of the wa-terway（Fig. 4a）, where it exceeded 0.6 m/s

（YANAI and OWADA, 1976）. Generally, earlier re-ports describe that water velocity of less than 0.6m/s is suitable for eelgrass bed formation（Ta-ble 1, MORITA and TAKESHITA, 2003）. Accordingly,the center of the waterway was thought to beunsuitable for the eelgrass bed formation. Al-though the water velocity in upper edge of thewaterway is slow（YANAI and OWADA, 1976）, theeelgrass bed formation might be inhibited be-cause of drying at low tide in these shallow areas

（intertidal zone）before the earthquake（Fig. 4c,

Table 1. Eelgrass growth conditions＊

Environmentalcondition

Threshold value

（1）Mud content less than 30%（2）Water velocity less than 0.6 m/s.（3）Shields parameter less than 0.2（4）Depth 1Ȃ2 m（not dried out）（＊MORITA and TAKESHITA, 2003; FISHERIES AGENCY OFJAPAN and MARINO-FORUM 21, 2007）

17Temporal change of eelgrass Zostera marina in Matsukawa-ura Lagoon

Table 1, GEOSPATIAL INFORMATION AUTHORITY OF

JAPAN, 2011）. However, the eelgrass bed expand-ed to these shallow areas after the earthquake

（Fig. 4d）. Change from intertidal to subtidalzone because of subsidence in these shallowareas might be regarded as a main factor of theeelgrass bed expansion in the lagoon. Groundsubsidence on the Oshika Peninsula in MiyagiPrefecture and Ofunato Bay in Iwate Prefecturewere reported to be approximately 100 cm and75 cm respectively; with other remarkable re-sults also on the Sanriku coast（GEOSPATIAL

INFORMATION AUTHORITY OF JAPAN, 2017）. In addi-tion, subsidence of approximately 30 cm was re-

ported in Soma City, Fukushima Prefecture（GEOSPATIAL INFORMATION AUTHORITY OF JAPAN,2017）, where the lagoon depth also became sev-eral tens of centimeters deeper in 2011（HIDAKA

et al., 2012）. However, dredging operations wereconducted during 2012Ȃ2013 in the waterway,where sand had been deposited by the tsunami.The dredged sand covered an area that hadbeen part of the clam fishery ground before thetsunami（Fig. 1b）. These areas dried out at lowtide after the sand coverage, and eelgrass didnot grow（Figs. 2b, 2c）. As explained above, therelief of growth inhibition with the increase ofwater depth because of subsidence might have

Fig. 4 Schematic diagram of the change in the spatial distribution of eelgrass bed (areasfilled in gray) caused by land subsidence after the earthquake in Matsukawa-ura Lagoon:a）vertical and c）horizontal distributions of eelgrass before the earthquake（2010）;b）vertical and d）horizontal distributions of eelgrass after land subsidence caused bythe earthquake.

18 La mer 56, 2018

contributed to the rapid eelgrass bed expansionin the shallow area which sand had not covered.

4. Implications for the future eelgrass bed dis-tribution

Much of the eelgrass bed in the Andaman Seacoast of Thailand was affected heavily by thetsunami following the earthquake in 2004

（WHANPETCH et al., 2010）. In Mangoku-ura Bay,located approximately 80 km north-northeast ofMatsukawa-ura Lagoon, although the eelgrassbed was not heavily affected by the tsunami fol-lowing the 2011 off the Pacific coast of TohokuEarthquake, the eelgrass bed decreased in lateryears（MURAOKA et al., 2016; NAKAOKA et al., 2017;SHOJI and MORIMOTO, 2016）. As negative effects ofapproximately 0.8 m of subsidence and low wa-ter transparency, the decrease mentioned abovemight derive from the low light penetration

（NAKAOKA et al., 2017; SHOJI and MORIMOTO, 2016）.In contrast to other coastal areas includingMangoku-ura Bay, the eelgrass bed expansionobserved in our study was thought to be the re-sult of the positive effect of the increase in waterdepth associated with the subsidence. However,the subsided ground has been returning gradual-ly around the lagoon as well as in other coastalareas of Sanriku （GEOSPATIAL INFORMATION

AUTHORITY OF JAPAN, 2017）. In the future, if theground and water depth in the lagoon were toreturn to their levels before the earthquake,then the growth inhibition of eelgrass attributa-ble to the drying would occur again（Table 1Ȃ4）.In other words, the area of eelgrass bed and thedistribution would be reduced to the pre-earthquake scale. Given the fact that the eel-grass bed had not increased substantially during2014Ȃ2015（Fig. 2）and the fact that the spatialdistribution of mud content had returned to thatin 2010（Fig. 3）, the eelgrass bed in the lagoonwould not expand further in the future.

In the coastal ecosystem, eelgrass is a funda-mentally important species that provides impor-tant ecosystem services. However, coastal devel-opment and climate change cause the global lossof eelgrass beds; protection and management ap-proaches are necessary to protect them fromfurther losses（WAYCOTT et al., 2009）. Althougheelgrass restoration programs have been launch-ed in many countries（ORTH et al., 2006）, restora-tion success with recovery of nursery function ofeelgrass is less than 30%（VAN KATWIJK et al.,2015）. Results of the present study show that theexpansion of upper edge of subtidal zone mightbe crucially important for eelgrass bed expan-sion in the lagoon, although we did not clarifythe recovery of the above nursery function ofeelgrass beds in this study. In addition, currenteelgrass beds in the lagoon are likely to decreasein the future. Accordingly, it is necessary tomonitor the eelgrass beds and their growth con-ditions in Matsukawa-ura Lagoon continuously.

AcknowledgementsWe thank Professor Hisayuki Arakawa,

Messrs. Ken Higuchi, Takehiko Ota and YuichiOkamura for their assistance in our study. We al-so thank Dr. Masami Hamaguchi for useful com-ments related to our study.

ReferencesABE, H., T. SATO, T. IWASAKI, T. WADA, T. TOMIYAMA,

T. SATO, M. HAMAGUCHI, N. KAJIHARA, and T.KAMIYAMA（2017）: Impact of the 2011 tsunami onthe Manila clam Ruditapes philippinarum popu-lation and subsequent population recovery inMatsukawa-ura Lagoon, Fukushima, northeast-ern Japan. Reg. Stud. Mar. Sci., 9, 97Ȃ105.

AKIMA, H. and A. GEBHARDT（2016）: Akima: Interpola-tion of Irregularly and Regularly Spaced Data. Rpackage version 0.6Ȃ2.

ARITA, K., T. YABE, and S. HAYASHI（2014）: Actual sit-uation of concentration and inventory of radioac-

19Temporal change of eelgrass Zostera marina in Matsukawa-ura Lagoon

tive cesium in Matsukawaura Lagoon sediment,Fukushima Prefecture. Society of Civil Engi-neers, Ser. G（Environment）70, III_225ȂIII_231.

（in Japanese）DUFFY, J. E., P. L. REYNOLDS, C. BOSTRÖM, J. A. COYER,

M. CUSSON, S. DONIDI, J. G. DOUGLASS, F. J. S. EKLÖ,A. H. ENGELEN, B. K. ERIKSSON, S. FREDRIKSEN, L.GAMFELDT, C. GUSTAFSSON, G. HOARAU, M. HORI, K.HOVEL, K. IKEN, J. S. LEFCHEK, P. -O. MOKSNES, M.NAKAOKA, M. I. Oʼ CONNOR, J. L. OLSEN, J. P.RICHARDSON, J. L. RUESINK, E. E. SOTKA, J. THORMAR,M. A. WHALEN and J. J. STACHOWICZ（2015）: Biodi-versity mediates top-down control in eelgrassecosystems, a global comparative-experimentalapproach. Ecol. Lett., 18, 696Ȃ705.

FISHERIES AGENCY OF JAPAN and MARINO-FORUM 21（2007）: Guideline for restoration of eelgrassbeds.（in Japanese）

GEOSPATIAL INFORMATION AUTHORITY OF JAPAN（2011）:Technical Report of the Geospatial InformationAuthority of Japan, D1ȂNo. 574. The Report ofLake and Wetland Survey of “Matsukawa-UraArea” in Fukushima. http: //www. gsi. go. jp/kankyochiri/shitsugenchousa-seika.html（in Japa-nese）

GEOSPATIAL INFORMATION AUTHORITY OF JAPAN（2017）:Six years from the 2011 off the Pacific coast ofTohoku Earthquake: A list of fluctuationamounts of coastal observation stations（height）.http://www.gsi.go.jp/common/000184909.pdf

HIDAKA, M., K. WAKUI, J. KAMIYAMA, K. TAKASAKI, R.NISHI, S. YAMASHITA and K. HAYASHI（2012）:Change in sediment characters and bathymetryin Matsukawaura inlet due to the Tsunami onMarch 11, 2011. Journal of Japan Society of CivilEngineers, Ser. B3（Ocean Engineering）68, I_186ȂI_191.（in Japanese）

HIJMANS, R. J.（2016）: Geosphere: Spherical Trigon-ometry. R package ver. 1.5Ȃ5.

IMAI, I., T. YAMAMOTO, K. ISHII, N. INABA and K.YAMAMOTO（2016）: Prevention of Harmful AlgalBlooms by Algicidal Bacteria Associated withEelgrasses. Journal of Water and Waste, 58,388Ȃ397.（in Japanese）

IWASAKI, H. and C. MATSUDAIRA（1954）: Studies of

Cultural Grounds of a Laver, Porphyra teneraKjellman in Matsukawa-Ura Inlet-I Environmen-tal Characteristics effecting upon Nitrogen andPhosphorus Contents of Laver. Nippon SuisanGakkaishi, 20, 112Ȃ119.（in Japanese）

KIKUCHI, T. and J. M. PERES（1977）: Consumer ecolo-gy of seagrass beds. In Seagrass ecosystems: ascientific perspective. MC ROY, C. P. andHELFFERICH, C.（eds.）, pp. 147Ȃ193, Marcel Dek-ker, New York.

KOMATSU, T., T. OHTAKI, S. SAKAMOTO, S. SAWAYAMA, Y.HAMANA, M. SHIBATA, K. SHIBATA and S. SASA

（2015）: Impact of the 2011: Tsunami on Seagrassand Seaweed Beds in Otsuchi Bay, SanrikuCoast, Japan, Marine Productivity: Perturbationsand Resilience of Socio-ecosystems, 43Ȃ53.

MORITA, K. and A. TAKESHITA（2003）: Estimation ofthe upper and lower critical depths for eelgrassbed formation. Doboku Gakkai Ronbunshu, 741,39Ȃ48.（in Japanese）

MURAOKA, D., D. SHIMIZU, N. SHIRAFUJI, H. TAMAKI, T.NODA, M. HAMGUSHI, Y. FUJINAMI and Y.MATSUMOTO（2016）: The IȂ7. Impact and recov-ery process of the Great East Japan Earthquakeand the following tsunami on Zostera meadows.Nippon Suisan Gakkaishi, 82, 142.（in Japanese）

NAKAOKA, M., H. TAMAKI, D. MURAOKA, M. TOKUOKA, T.KOMATSU and N. TANAKA（2017）: Temporalchanges in seagrass beds of Sanriku Coast be-fore and after the Great East Japan Earthquake.Nippon Suisan Gakkaishi, 83, 659Ȃ663.（in Japa-nese）

NISHI, R., J. MANU, T. JANSEN and K. HAYASHI（2012）:Scarp generation behind a dune and shore pro-tection structure by Tsunami on March 11, 2011.Journal of Japan Society of Civil Engineers, Ser.B3（Ocean Engineering）, 68, I_198ȂI_203.（inJapanese）

OKADA, T. and K. FURUKAWA（2013）: Sediment condi-tions for restoration of eelgrass（Zostera mari-na）damaged by Tsunami in Miyako Bay. Jour-nal of Japan Society of Civil Engineers, Ser. B3

（Ocean Engineering）, 69, I_31ȂI_36.（in Japa-nese）

ONISHI, Y., Y. MOHRI, A. TUJI, K. OHGI, A. YAMAGUCHI

20 La mer 56, 2018

and I. IMAI（2014）: The seagrass Zostera marinaharbors growth-inhibiting bacteria against thetoxic dinoflagellate Alexandrium tamarense.Fish. Sci., 80, 353Ȃ362.

ONO, T., Y. TERAI and T. OKAMOTO（1972）: Productiv-ity of Nori Culture Farm in Matsukawa-Ura In-let. Bull. Fukushima Pref. Exp. Stat., 1, 17Ȃ33.（inJapanese）

ORTH, R. J., T. J. B. CARRUTHERS, W. C. DENNISON, C. M.DUARTE, J, W. FOURQUREAN, K. L. HECK, A. R.HUGHES, G. A. KENDRICK, W. J. KENWORTHY, S.OLYARNIK, F. T. SHORT, M. WAYCOTT and S. L.WILLIAMS（2006）: A Global Crisis for SeagrassEcosystems. BioScience, 56, 987Ȃ996.

R DEVELOPMENT CORE TEAM（2016）: R: A languageand environment for statistical computing. RFoundation for Statistical Computing, Vienna,Austria.

SAKAMAKI, T. and O. NISHIMURA（2014）: Impacts of theGreat East Japan Earthquake on coastal ecosys-tems of Miyagi Prefecture. Journal of Japan Soci-ety of Civil Engineers, Ser. B3（Ocean Engineer-ing）, 70, I_31ȂI_36.（in Japanese）

SAKAMAKI, T., Y. SAKURAI and O. NISHIMURA（2016）:Tsunami impacts on eelgrass beds and acute de-terioration of coastal water quality due to thedamage of sewage treatment plant in Matsushi-ma Bay, Japan In: Santiago-Fandino, V., Tanaka,H., Spiske, M.（eds）Tsunamis and earthquakesin coastal environments: significance and resto-ration. Springer. 222 pp.

SASA, S., S. SAWAYAMA, S. SAKAMOTO, R. TSUJIMOTO, G.TERAUCHI, H. YAGI and T. KOMATSU（2012）: Didhuge tsunami on 11 March 2011 impact seagrassbed distributions in Shizugawa Bay, SanrikuCoast, Japan? Proc. SPIE 8525, Remote Sensingof the Marine Environment II, 85250X.

SASAKI, H., K. OTANI and Y. SAKURAI（2016）: Disap-pearance of Zostera Beds in Matsushima Bay bythe Great East Japan Earthquake Disaster andActivities toward their Regeneration. Journal ofWater and Waste, 58, 315Ȃ320.（in Japanese）

SATO, T., Y. OGATA, Y. NEMOTO and S. SHIMAMURA

（2007）: Status Review and Current Concerns ofthe Fishery for the Short-neck Clam, Ruditapes

philippinarum, in Matsukawaura Lagoon, Fu-kushima Prefecture. Bull. Fukushima Pref. Exp.Stat., 14, 57Ȃ67.（in Japanese）

SHOJI, J. and M. MORIMOTO（2016）: Changes in fishcommunity in seagrass beds in Mangoku-uraBay from 2009 to 2014, the period before and af-ter the tsunami following the 2011 off the Pacificcoast of Tohoku earthquake. J. Oceanogr., 72,91Ȃ98.

SHORT, F. T. and D. M. BURDICK（1996）: Quantifyingeelgrass habitat loss in relation to housing devel-opment and nitrogen loading in Waquoit Bay,Massachusetts. Estuaries, 19, 730Ȃ739.

VAN KATWIJK, M. M., A. THORHAUG, N. MARBÀ, R. J.ORTH, C. M. DUARTE, G. A. KENDRICK, I. H. J.ALTHUIZEN, E. BALESTRI, G. BERNARD, M. L.CAMBRIDGE, A. CUNHA, C. DURANCE, W. GIESEN, Q.HAN, S. HOSOKAWA, W. KISWARA, T. KOMATSU, C.LARDICCI, K.-S. LEE, A. MEINESZ, M. NAKAOKA, K. R.O'BRIEN, E. I. PALING, C. PICKERELL, A. M. A.RANSIJN and J. J. VERDUIN（2015）: Global analysisof seagrass restoration: The importance of large-scale planting. J. Appl. Ecol., 53, 567Ȃ578.

WAYCOTT, M., C. M. DUARTE, T. J. B. CARRUTHERS, R. J.ORTH, W. C. DENNISON, S. OLYARNIK, A. CALLADINE,J. W. FOURQUREAN, K. L. HECK, JR., A. R. HUGHES, G.A. KENDRICK, W. J. KENWORTHY, F. T. SHORT and S.L. WILLIAMS（2009）: Accelerating loss of sea-grasses across the globe threatens coastal eco-systems. PNAS, 106, 12377Ȃ12381.

WHANPETCH, N., M. NAKAOKA, H. MUKAI, T. SUZUKI, S.NOJIMA, T. KAWAI and C. ARYUTHAKA（2010）:Temporal changes in benthic communities ofseagrass beds impacted using a tsunami in theAndaman Sea, Thailand. Estuar. Coast. Shelf Sci.,87, 246Ȃ252.

YANAI, N. and K. OWADA（1976）: Flow situation of af-ter channel digging in Matsukawaura. Bull. Fu-kushima Pref. Exp. Stat., 4, 115Ȃ120.（in Japa-nese）

Received: September 17, 2017Accepted: February 20, 2018