Algal Resources (2013) 6：1-13

Distributions of species along the coasts of Prefecture, locating at the northernmost of ,

Shinji KIRIHARA1*, Naoto KON２, Daisuke FUJITA３ and Masahiro NOTOYA４

Abstract : Distribution and standing crops of Zosteraceae species were surveyed along the coasts of , locating at the northernmost of Honshu, Japan, from 1999 to 2002. Sampling were made at depths of 2.5 m (1,079 points), 5 m (1,181 points) and 10 m (1,183 points) on transects set at about 500 m intervals along the whole coasts divided in four areas according to oceanographic and topographic characteristics: the Japan Sea coastal area affected by Tsushima (warm) Current, the Pacific coastal area affected by Oyashio (cold) Current, coastal areas facing to the connecting the two seas, and coastal areas of embayed by Tsugaru and . Distribution patterns of Zosteraceae species can be summarized as below. iwatensis Makino: common on bedrocks along the Tsugaru Straight and Pacific coast but absent in Mutsu Bay; Zostera marina Linnaeus: common on soft bottoms of Mutsu Bay and Tsugaru Straight areas but absent in the Pacific coast; Z. caespitosa Miki: common on soft bottoms of Tsugaru Strait and Mutsu Bay; Z. caulescens Miki: restricted to a depth of 10 m in Tsugaru Strait coast. In Mutsu Bay, distributions of Z. marina and Z. caespitosa rarely overlapped and the latter species showed a tendency to grow in deeper depths. Sediment analyses of their habitats revealed that Z. caespitosa were likely to grow in the habitat with thinner sediment layer and coarser particle than Z. marina.

Keywords : Zosteraceae, Zostera marina, Zostera caespitosa, Zostera caulescens, Phyllospadix iwatensis, distribution of seagrass, Aomori Prefecture

Introduction Center of Japan 1994). Aomori Prefecture is located at the northernmost of Honshu Island Seagrass meadows are important for coastal and has the second largest seagrass meadows in environment and fisheries because they diver- total areas (7,271 ha) in Japan, following 17,071 sify both habitats and living organisms in ha of those in (Environment Agency coastal waters, improve water quality and pro- and Marine Parks Center of Japan 1994). mote sedimentation (Hemminga and Duarte The coastal area of Aomori Prefecture is 2000). In Japan, Zosteraceae species are major geographically divided into four sub-areas, that components of the seagrass meadows (Miki is, Japan Sea, Pacific Ocean, Tsugaru Strait and 1933) and the total area of the domestic Mutsu Bay areas. These areas are affected seagrass meadows was estimated to be 49,464 differently by both Tsushima (Tsugaru) warm ha (Environment Agency and Marine Parks and Oyashio cold Currents and show different

1 Fisheries Bureau, Aomori Prefectural Government, Aomori, Aomori 030-8570, Japan 2 MAC Co. Ltd., Kugurizaka, Aomori, Aomori 038-3212, Japan 3 Tokyo University of Marine Science and Technology, Konan, Minato-ku, Tokyo 108-8477, Japan 4 Notoya Research Institute of Applied Phycology, Taitoo-ku, Tokyo 108-8477, Japan ＊Correspondence author : e-mail : [email protected]

1 Shinji KIRIHARA,NaotoKON, Daisuke FUJITA and Masahiro NOTOYA

Fig. 1. Map of Aomori Prefecture showing location of major survey points and area di- vision. oceanographic characteristics. In addition, topo- Materials and methods graphic characteristics are also quite different among them, e.g., though Japan Sea and Pacif- The biomass survey of Zosteraceae species ic Ocean area are directly facing to open oceans, was conducted from 1999 to 2002. In the sur- Mutsu Bay area is a semi-closed area which vey, 1,183 transects in total were set at about 500 is deeply embayed between Shimokita and m intervals along the whole coasts of Aomori . Therefore, the distribution Prefecture except for port areas (Fig. 1). On each of Zosteraceae species along the coasts of the transect, sampling and observation were made Aomori Prefecture is interesting from the bio- at depths of 2.5 m (1,079 points), 5 m (1,181 geographical point of view. points) and 10 m (1,183 points) and totally 3,443 Furthermore, the seagrass meadows are used points were observed by SCUBA diving (Table as important fishery grounds, as well as spaw- 1). On transects set along a long sandy beach ning, nursery and feeding grounds of fish and which is approximately 50 km long in the shellfish (e.g. sea cucumbers, flounders) in Ao- middle of the Pacific coast area, sampling could mori Prefecture. However, information of the not be conducted at a depth of 2.5 m because seagrass meadows in Aomori Prefecture has of adverse physical conditions of high waves. been limited to parts of nation-wide floristic At each observation point, quadrates of 25m2 studies (Miki 1933; Tanaka et al. 1962; Omori (5 × 5 m) were placed and substratum charac- 1993, 2000) and a local biomass survey (Notoya teristics was categorized in the following five and Aruga 1992). Therefore, the authors con- categories; bedrock, boulder (diameter ca. 256 ducted a detailed survey on the distribution of mm ＜), gravel (2 - 256 mm), sand (0.1 - 2 mm) seagrass along the whole coasts of Aomori and mud (0.1 mm ＞). At soft substrata (sand or Prefecture from 1999 to 2002. In the present mud), sediments were sampled within the paper, we report the horizontal and vertical quadrates after thickness of sediments (up to 1 distribution of Zosteraceae species along the m in thickness) were measured using a gradu- coasts of Aomori Prefecture and discuss the ated bar. The sampled sediments were dried environmental factors affecting these distribu- and sieved to measure the size distribution of tional patterns. particles. Median particle diameter (φ50) of these samples were read from cumulative frequency curves about seven particle sizes of Wentworth

2 Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan

Table 1. Number of survey points in each district and depth

(1922)'s class terms; granules (particle diameter standing crop. The frequency in occurrence is 2mm＜), very coarse sands (1 - 2 mm), coarse the ratio of the number of observation points sands (0.5 - 1 mm), medium sands (0.25 - 0.5 where the species appears to the total number mm), fine sands (0.125 - 0.25 mm), very fine of points. Standing crop of each species was sands (0.63 - 0.125 mm) and silts (0.063 mm ＞). measured in a wet weight of samples after they Asmallerquadrate(50× 50 cm = 0.25 m2)was were brought back to the laboratory at Aomori placed on a patch of each Zosteraceae species Prefectural Fisheries Research Center. in the large quadrate (25 m2)tosampleand Pentad average seawater temperatures from estimate standing crops. Distribution of each 1985 to 2002 on the nine sites (Fukaura, Aji- species along the coast of Aomori Prefecture gasawa, Mimmaya, , Sai, , was described as frequency in occurrence and Rokkasho, and Hashikami) of Ao-

3 Shinji KIRIHARA,NaotoKON, Daisuke FUJITA and Masahiro NOTOYA

mori Prefectural coasts were obtained from the data of“UODAS”report (Aomori Prefectural Fisheries Research Center 2004).

Results

Seawater temperature Seasonal changes in pentad average seawater temperature at the nine sites of Aomori Pre- fectural coasts are shown in Fig. 2. The aver- aged seawater temperatures of sites in the Ja- pan Sea area (Fukaura, Ajigasawa), at the northern coast of Tsugaru Peninsula (Mim- maya), at the coast of Mutsu Bay (Hiranai), at the northern coast of Shimokita Peninsula (Sai, Kazamaura)andatthecoastofthePacific Fig. 2. Seasonal changes of average sea water tem- Ocean (Rokkasho, Hachinohe, Hashikami) were perature at nine coastal sites in Aomori Pre- in the range of 6.6 - 25.5 ℃,7.7- 23.4 ℃,7.2- fecture (Aomori Prefectural Fisheries Research Center 2004). See Fig. 1 for alphabets in 23.7 ℃,6.6- 23.3 ℃ and 5.3 - 21.1 ℃, respectively. parentheses showing locations. There was a tendency that seawater tempera- ture was higher at the sites in the western ar- ea of Aomori Prefecture. substrata observed between Cape Shiriya and Cape Nakayama（‘v - w’）and near Hashika- Substratum characteristics mi（‘y-z’）. Distribution of five types of substrata on the Median particle diameters of sediments sam- whole coast of Aomori Prefecture is shown in pled from 2,009 points (58.4％ to total points) Fig. 3. dominated by soft bottom (sand or mud) were Along the Japan Sea coast, bedrock was showninTable2. dominant in the southern area（area‘b’）and The mean median particle diameter of sedi- northern area（‘f’）with the exception of a long ments averaged on five coasts (Japan Sea, sandy beach (about 40 km) in the middle area westernpartofthecoastfacingtoTsugaru （‘c - e’）.Intheareas‘g-i’along the coast Strait, Mutsu Bay, eastern part of the coast between Cape Tappi and Cape Myojin facing facing to Tsugaru Strait and the Pacific Ocean) to the Tsugaru Strait, coastal substrata were were in the range of 0.36 - 0.44 mm, 0.38 - 0.64 mainly composed of bedrocks or boulders with mm, 0.29 - 0.52 mm, 0.33 - 0.54 mm and 0.30 - the exception of the soft bottoms in Minmaya 0.32 mm, respectively. Bay（Fig. 3,‘g - h’）.AlongthecoastofMut- su Bay（‘i-q’）, sand, mud or gravel was Distributions and abundance of Zosteraceae dominant except for the area ‘l’along the species Natsudomari Peninsula coast where boulder In the present study, four Zosteraceae spe- was dominant. Along the coast of Ashizaki Bay cies, Zostera marina Linnaeus, Z. caespitosa （‘o, p’）, muddy sea bottom was prominently Miki, Z. caulescens Miki and Phyllospadix iwat- dominant. Along the coast of Shimokita Penin- ensis Makino were recorded along the coast of sula between Cape Kai and Cape Shiriya fac- Aomori Prefecture. ing to the Tsugaru Strait, bedrock or boulder Zostera marina was dominated（Fig. 3,‘r - v’）,withtheex- Z. marina was the most common among the ception of muddy substrata in Ohata Bay（‘u’）. four Zosteraceae species, which was obtained Along the Pacific coast, most of sea bottom was from 220 points (70, 114 and 36 points at depths composed of sand except for the rocky/stony of 2.5, 5 and 10 m, respectively) along the coast

4 Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan

Fig. 3. Distribution (in coverage) of bottom substrata on transects set at 500 m intervals along Aomori Prefecture. See Fig. 1 for alphabets showing locations.

Table 2. Median particle diameter (SD) of sediments at the depth of 2.5 m, 5 m, 10 m

5 Shinji KIRIHARA,NaotoKON, Daisuke FUJITA and Masahiro NOTOYA

Fig. 4. Distributions of Zosteraceae species in each depth along the coast of Aomori Prefecture, showing amounts of standing crops by circle size. Numerals show the number of points of occurrence.

Fig. 5. Standing crops and frequencies (ratio of habitats of each species to total survey points) of four Zosteraceae species in Aomori prefecture. Solid bar: 2.5m in depth; stripe: 5m in depth; open: 10m in depth; n: not found.

6 Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan of Aomori Prefecture. Among them, 75.0 ％ (165 ding into the bay. Z. caespitosa coexisted with Z. points) of these points were in the Mutsu Bay marina at five points in Mutsu Bay. Frequency area (Fig. 4). These points were exclusively in occurrence of the points where Z. caespitosa comprised of sandy or muddy bottoms. Mean and Z. marina coexisted was 0.4％ of total sur- standing crop and frequency in occurrence in vey points in the bay. Along the Shimokita the total survey points of Z. marina at a depth Peninsula coasts in the Tsugaru Strait area, Z. of 5 m in Mutsu Bay were 98.6g m-2 and 24.2 ％, caespitosa were found only at one point (2.5 m respectively. Each of these values was the high- in depth) near Cape Ohma (Fig. 1,‘s’）and four est among Z. marina standing crop and fre- points (2.5 or 10 m in depth) at the western coast quency in occurrence of the four areas at the of Cape Shiriya (Fig. 1,‘v’）. depth of 5 m (Fig. 5). In Mutsu Bay, Z. marina Zostera caulescens was particularly abundant along the western Z. caulescens was found at 19 points with coast of the bay and around Ashizaki Bay. sandy sea bottom in the Tsugaru Strait area, Other than in Mutsu Bay, the 23.6 ％ (52 points) and they were only at a depth of 10 m (Fig. 4). of the total Z. marina habitats was located along Four of these points were located near Cape the coast of Tsugaru Strait (30 points at Tappi (Fig. 1,‘g’）and other 15 points located Tsugaru Peninsula; 22 points at Shimokita Pe- along the coast of Cape Ohma (Fig. 1,‘s’）to ninsula). Z. marina was most frequently recor- Cape Shiriya (Fig. 1,‘v’）.Meanstandingcrops ded from Tairadate (17 points around‘h’in (frequencies in occurrence) were 120.9g m-2 (4.1 Fig. 1) near the mouth of Mutsu Bay. Mean ％) and 97.1g m-2 (7.8 ％) in these areas, respec- standing crops (frequencies in occurrence) at tively. depths of 2.5, 5 and 10 m, respectively, were Phyllospadix iwatensis 31.4g m-2 (5.2％), 76.4g m-2 (10.3％) and 156.2g m-2 P. iwatensis was obtained from 67 points (32, (15.3％) at the points along the Tsugaru Penin- 29 and 6 points at depths of 2.5, 5 and 10m, sula coast, while 48.1g m-2 (5.7％)，19.0g m-2，(4.7 respectively) (Fig. 4). This species, growing only ％) and 0.8g m-2 (1.0％)atdepthsof2.5,5and10 on bedrocks, was not found in Mutsu Bay. m, respectively, at the points along the Shimo- Among the 67 points, 59.7％ (40 points: 14 points kita Peninsula coast (Fig. 5). In many cases, Z. at Tsugaru Peninsula; 26 points at Shimokita marina was observed mainly in inlets or areas Peninsula) of those was located in the Tsuga- protected by breakwaters along the Tsugaru ru Strait area. Mean standing crops (frequen- Strait coast. Along the Japan Sea coast, Z. cies in occurrence) at depths of 2.5 , 5 and 10 m marina was obtained only from three points in in the Tsugaru Peninsula area were 5.3g m-2 inlets, i.e. one point (10 m in depth) at Cape (3.1％)，39.1g m-2 (6.2％)and55.9gm-2 (5.1％), Gongen（‘f’）andtwopoints(5mindepth)at respectively, while those in the Shimokita Iwasaki（‘a’）. Peninsula area are 37.4g m-2 (5.7％)and18.0gm-2 Zostera caespitosa (7.8 ％) at depths of 2.5 m and 5 m, respective- Z. caespitosa was obtained from 151 (35, 47 and ly (Fig. 5). Along the coast facing to Tsugaru 69 points at depths of 2.5 m, 5 m and 10 m, Strait, P. iwatensis was particularly abundant at respectively) points (Fig. 4). Substrata of Z. points near Cape Ohma (Fig. 1,‘s’）and Cape caespitosa habitats were sandy, muddy or grav- Takano (Fig. 1,‘h’）. The habitats of P. el bottoms in Mutsu Bay (sharing 96.7％ by 146 iwatensis alongthePacificcoasts(26points) points in the total points) and Tsugaru Penin- shared 38.8％ of its total occurrence; mean sula coasts of Tsugaru Strait (sharing 3.3％ by standing crops (frequencies in occurrence) were 5 points). In Mutsu Bay, mean standing crops 96.9g m-2 (13.9％), 10.1g m-2 (3.7％) and 0.44g m-2 (frequencies in occurrence) were as high as 116.5 (0.5％) at depths of 2.5, 5 and 10 m, respectively. gm-2 (8.3 ％), 130.9 g m-2 (12.2 ％) and 157.3 g m-2 In the Japan Sea and Mutsu Bay areas, P. (17.6 ％) at depths of 2.5, 5 and 10 m, respec- iwatensis was collected only at one point (2.5 m tively. Z. caespitosa was also found on relative- depth) from each area. Since P. iwatensis grows ly wavy areas such as points at capes protru- on bedrock, it never occurred with sand-dwelling

7 Shinji KIRIHARA,NaotoKON, Daisuke FUJITA and Masahiro NOTOYA

Zosteraceae species but with macroalgae such 20 cm. Standing crop (mean ± SD) of Z. marina as laminarialean (e.g., Saccharina japonica (J.E. growing on ＞ 20 cm thick sediments (466 ± 497 Areschoug) C.E. Lane, C. Mayes, Druehl and gm-2) was 1.2 times higher than that on thin- G.W. Saunders, Ecklonia stolonifera Okamura) ner ones (373 ± 344g m-2). Sediments sampled or fucalean (e.g., Myagropsis myagroides (Mertens from 80.1％ of Z. marina habitats were less than ex Turner) Fensholt, Sargassum confusum Agar- 0.25 mm in median particle diameter. The stand- dh) species. ing crop (mean ± SD) of Z. marina growing on Relationships between standing crops and soft these fine sediments (453 ± 487g m-2)wassimi- bottom characteristics lar to that of coarse (more than 0.25 mm medi- Relationships between standing crops of Zos- an particle diameter) sediments (506 ± 495g m-2). teraceae species and sediment characteristics Z. caespitosa was found to grow on sedi- (e.g., thickness and median particle diameter) ments of ＞ 3 cm thick (Fig. 6). In 30.3％ of Z. are shown in Fig. 6. In 92.5 ％ of Z. marina caespitose habitats, thickness of sediments were habitats, thickness of sediments were more than less than 20 cm. Standing crop (mean ± SD) of Z. caespitosa on these thin sediments (1,494 ± 1,037g m-2) was 1.5 times higher than that on sediments thicker than 20 cm (986 ± 1,041g m-2). Fifty-five percents of Z. caespitosa habitats were on the sediments of medium to very coarse sand. Standing crop (mean ± SD) of Z. caespitosa growing on these coarse sediments (1,359 ±1,146 gm-2) was 1.6 times higher than that on silt, fine and very fine sand sediments (870 ± 885g m-2). Z. caulescens was found to grow on the sedi- ments between 15 and 80 cm thick. Median particle diameter of its habitats was between 0.16 and 0.30 mm (Fig. 6).

Discussion

In the present survey, quantified distributional data of four Zosteraceae species previously re- ported from Aomori Prefecture (Miki 1933; Tanaka et al. 1962; Omori 1993, 2000; Notoya and Aruga 1992) were obtained through the whole prefectural coast. Here we discuss the distribu- tional pattern and its growth condition of each species. Z. marina has been reported as a cosmopolitan species, distributing on temperate to subarctic coasts of northern hemisphere (den Hartog 1970). In the present study, large populations of Z. marina were found in Mutsu Bay. Along the Japan Sea and the Pacific coasts, however, Z. marina was rare or absent, though dozens of Fig. 6. Relationships between thickness of sediment, kilometre long sandy bottoms were present on median particle diameter and standing crops the both coasts. Several reports (Kawasaki et al. (circle size) of three sand-dwelling Zosteraceae 1990; Douke et al. 2000; Morita et al. 2002) species along the coast of Aomori Prefecture. showed that the distribution of Z. marina was

8 Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan

Table 3. Mean values (range) of Shiels number calculated for each sea area and depth

limited by the movement of sediments. Shields Prefecture. number is used as an indicator of wave action Z. caespitosa was reported to occur in Hokkaido, and sand movement in optimization of stock northern Honshu and east Korea (Miki 1933). enhancement of Z. marina (Maruyama et al. The specimen of this species have been col- 1988). Shields numbers obtained from Z. marina lected from three points in Aomori Prefecture, habitats (2.5 to 10 m in depth) in this study are that is, Harada (Sai Village, Fig. 1,‘r’）in 1957, shown in Table 3. These values were calcula- Asamushi (Aomori City, Fig. 1,‘k’）and Nohe- ted by using significant wave heights and peri- ji (Fig. 1,‘m’）in 1990-1991, and Asamushi in ods measured at 65 sites of fishing ports of the 1999 (Omori 1993; Tanaka et al. 2003). It has prefecture (The Japanese Institute of Technology not been obtained in the Japan Sea area and the on Fish Port and Communities 1984-1988), me- Pacific coastal area of Aomori Prefecture, up to dian particle diameters of the sediment (Table now. 2), and assuming the specific gravity of sand In the present study, the extensive stands of to be 2.65. According to Kawasaki (2003), Z. Z. marina and Z. caespitosa were observed in marina population could not maintain in the Mutsu Bay. But the ratios of sympatric habi- sediment condition of ＞ 2 in Shields number. tats to total Z. caespitosa or Z. marina habitats According to his conclusion, most bottoms at in Mutsu Bay were only 3.4％ and 3.0％,re- depths of 2.5 - 10 m in Mutsu Bay and 5 - 10 m spectively, showing that they largely grew allo- on Tsugaru Strait were suitable for propaga- patrically. In Mutsu Bay, standing crops and tion of Z. marina. On the contrary, Shields frequencies in occurrence of Z. caespitosa in- numbers of the bottoms in the Japan Sea and creased at deeper points, while those of Z. the Pacific coastal areas were so large as 3.7 - marina attained the maximum values at 5 m in 14.2 and 2.6 - 11.1, respectively. This may ex- depth (Fig. 5). Therefore, the habitual depth plain the highest frequency in occurrence of Z. was different between the two species. The ran- marina occurs in Mutsu Bay and its rarity or ges of habitual depths (and depths attaining the absence in the Japan Sea and Pacific coastal maximum standing crops or densities) of Z. areas. The level of physical turbulence of the caespitosa and Z. marina at several sites are as sediment can be one of factors to determine the follow: 1.6 - 6.5 m (2 - 5m)and0.6- 5.4 m (0.6 m) distribution of Z. marina along the coasts of in Lake Notoro (Takahashi et al. 1997), 4 - 12 m Aomori Prefecture. (7 - 9m)and1- 10 m (3 - 5 m) at Noto-Ukai Water temperature is also one of environ- (Taniguchi and Yamada 1979) , 3 - 20 m (10 m) mental factors to be discussed here because and 3 - 7 m (3 m) at Iwaki on Noto Peninsula Kawasaki et al. (1986) reported that young Z. (Tajima and Sano 1980), respectively. As shown marina died at water temperature of 30℃ above, the distribution of Z. caespitosa are in a month but never died under 25℃.Asshown deeper than that of Z. marina. Here we dis- in Fig. 2, however, pentad average water tem- cuss the allopatrical patterns in the distribu- perature never went up to 25.5 ℃ in nine sites tion of the two species on the viewpoint of along Aomori prefectural coasts. Therefore le- physical characteristics of substrata. thal high water temperatures may not be a de- In the present study, standing crops and fre- terminant of Z. marina distribution in Aomori quencies in occurrence of Z. caespitosa were

9 Shinji KIRIHARA,NaotoKON, Daisuke FUJITA and Masahiro NOTOYA larger on thinner and coarser sediments rather cies has not been obtained from the Pacific than Z. marina (Fig. 6). Rhizomes of Z. marina coastofAomoriPrefectureuptonow.Inthe extend horizontally in sediments, while those of vicinities of Asamushi or Moura where Omori Z. caespitosa grow vertically or obliquely with (1993) found populations of Z. caulescens, we short internodes (Omori and Aioi 1998). Occur- obtained Z. marina and Z. caespitosa but could rence of Z. marina was limited to sandy or not Z. caulescens. There might have been suc- muddy bottoms probably because of easiness cession of the flora from Z. caulescen to Z. to extend branched rhizomes in such sediments marina or Z. caespitosa. (Ogawa 1987). In coarser and thinner sediments, Z. caulescens develops an extraordinarily long Z. caespitosa may be more adaptable than Z. flowering shoot up to 7.8 m in length (Nakaoka marina because it can make clumps with short and Aioi 2001). We could observe flowering rhizomes. Therefore the difference in rhizome shoots of 4 m in length at Cape Ohma. Leaf morphology and its elongation pattern between blades occurring from long flowering shoots the two species might be attributable to the may benefit them by reaching the depth zone of difference in the sediment characteristics of better light conditions when grown in deeper their habitats. water (Omori 1994, Omori and Aioi 2000). In Light is another possible determinant of allo- the Tsugaru Strait area, Z. caulescens was found pathic nature of the two species, particularly, at deeper points (10 m depth) than Z. marina the segregation in their vertical distribution. and Z. caespitosa as shown by Miki (1933). Z. Maegawa (2004) demonstrated that daily com- caulescens was not found on shallower (2.5 and pensation point of young Z. caespitosa from 5 m depth) sandy or muddy bottoms where Mutsu Bay was only 1.9 ％ of sea surface at 15 more light is available, though its range of ha- ℃,whileZ. marina from Ise Bay was 5.7 ％ at bitual sediments were relatively wide in layer the same temperature. Using these data, he thickness and particle size (Fig. 6). The sedi- suggested that the difference of light require- ment movement can be one of limiting factors ment between the two species determined their of Z. caulescens because Shields numbers re- growth depths. As the light requirement for markably increased at shallow points in the growth of Z. marina varies by habitual condi- Tsugaru Strait area (Table 3). tions (Abe et al. 2003), further study is needed P. iwatensis is reported to occur along the to compare light requirements between the two northwestern coasts of the Pacific Ocean, that species by using samples collected from sym- is, on the coasts of Hokkaido, middle and patric habitats in order to discuss the differ- northern Honshu, Korea, and Sakhalin ence in the growing depth. (Omori 2000). Vertical range of its distribution Z. caulescens is reported to occur on the cen- was known as 1 - 8 m in depth (Miki 1933). tral to northern coast of Honshu, and Korean Furthermore, Yabe et al. (1996) reported that P. Peninsula (Miki 1933). Recent papers reported iwatensis did not seem to adapt to grow in the the presence of other populations at several subtidal zone where there was shortage of sites in Honshu and Korean Peninsula (Nakaoka light compared with intertidal zone. Along the and Aioi 2001). There have been no records Tsugaru Peninsula coast in the Tsugaru Strait from Hokkaido and north of Korean Peninsu- area, however, standing crops of P. iwatensis la. Therefore, Cape Ohma is considered as the increased at deeper points and reached maxi- northern boundary of the distribution of Z. mum 1.4kg m-2 at a depth of 10 m off Cape caulescens in the world. Takano (Fig. 4). Therefore, P. iwatensis seems to Z. caulescens had been collected from several be able to form populations in deeper depth points along the Aomori prefectural coast: than previously reported. Miki (1933) consid- Ajigasawa (Fig. 1,‘c’）in 1910; Ohata (Fig. 1,‘u’） ered that geographical distribution of P. iwaten- in 1955 and Wakinosawa (Fig. 1,‘q’）in 1988- sis is related to the effects of cold currents. But 1989, Asamushi and Moura (Hiranai Town, Fig. this is a misunderstanding because P. 1,‘l’）in 1990 (Omori 1993). However, this spe- iwatensis is obtained along the coasts of Japan

10 Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan

Sea and Tsugaru Strait which is affected by growth of Zostera marina in central Japan. warm Tsushima Current in the present study. Fish. Sci. 2003; 69: 890-895. In the present study, Zostera japonica Ascher- Aomori Prefectural Fisheries Research Center. son and Graebner was found only in the inter- “UODAS”report on oceanic sea and fish- tidal zone (about 0.5 m depth) at Asamushi or ing conditions. 2004; No. 1263-1333:pp.5-6. Ashizaki in Mutsu Bay. Z. japonica is widely den Hartog C. The seagrasses of the world. distributed along the coasts of Japan and al- North Holland Pub. Co., Amsterdam. 1970. ways found at depths shallower than 1 m and Douke A, Itani M, Yoshiya M. Some aspects of in the intertidal zone (Nakaoka and Aioi, 2001). eelgrass (Zostera marina) communities in However, we omit this species from further Maizuru Bay. II. Limit factors on eelgrass discussion here because of absence in deeper distribution. Bull. Kyoto Inst. Ocean. Fish. subtidal areas and lack of quantitative data. Sci. 2000; 22: 29-35 (in Japanese). As described in introduction, seagrass mead- Environment Agency, Marine Parks Center of ows are known as important nursery of com- Japan. The report of the marine biotic en- mercial fish and shellfish. During the present vironment survey in 4th national survey on survey, a lot of juveniles or young fish (Se- the natural environment. Vol. 2. Algal and bastes thompsoni (Jordan & Hubbs), S. inermis sea-grass beds. 1994; 11-44 (in Japanese). Cuvier, Chrysophrys major Temminck & Schle- Hemminga MA, Duarte CM. Seagrass Ecology. gel, etc.), sea cucumbers (Stichopus japonicus Cambridge University Press, Cambridge. Selenka), sea urchins (Strongylocentrotus nudus 2000. (A. Agassiz), S. intermedius (A. Agassiz)) and Kawasaki Y. Restoration and creation of the crabs (Telmessus acutidens Stimpson) were ob- function of seagrass community (Zostera served in seagrasss meadows. These meadows bed). Aquabiology 2003; 25: 85-91 (in Japa- are particularly important at sandy or muddy nese). bottoms where laminarialean and fucalean spe- Kawasaki Y, Izuka T, Goto H, Terawaki T, cies hardly grow as in Mutsu Bay. Neverthe- ShimoS.EffectoftemperatureonZostera less, seagrass meadows were reported to de- marina L: I. Seed germination and seeding crease by 369 hectares in the bay from 1978 to development. CRIEPI report No. 485028, 1991 (Environment Agency and Marine Parks Abiko Research Laboratory, Central Re- Center of Japan 1994). We believe that the search Institute of Electric Power Industry, present data, particularly quantitative data on Abiko. 1986; 1-18 (in Japanese). seagrass distribution and habitual bottom char- Kawasaki Y, Ishikawa Y, Maruyama K. acteristics can provide scientific bases to be used Techniques for selecting appropriate site to in future restoration projects. create eelgrass (Zostera marina)Meadows. Bull. Coast. Ocean.1990; 27 : 136-145 (in Jap- Acknowledgements anese). Maegawa M. Growth and photosynthesis of We thank Prof. M. Nakaoka (Hokkaido Uni- seagrass Zostera caespitosa. Rep. of Lab. versity) and Dr. Y. Omori (Yokosuka City Phycol. Fac. Biores. Mie Univ. 2004. Museum) for information on seagrass litera- Maruyama K, Igarashi Y, Ishikawa Y, Kawasaki ture and identification of seagrass species. We Y. Development of techniques for marine also appreciate K. Morita (Tokyo Kyuei Co. macrophytebedcreationinthecoastalzone Ltd.) for his technical advice on the Shields near a power - 8. Estimation method of number. stability of sands bed. CRIEPI report U 87069, Abiko Research Laboratory, Central References Research Institute of Electric Power Indus- try, Abiko. 1988; 19-23 (in Japanese). Abe M, Hasegawa N, Kurashima A, Maegawa Miki S. On the sea-grass in Japan (I), Zostera M. Estimation of light requirement for the and Phyllospadix, with special reference to

11 Shinji KIRIHARA,NaotoKON, Daisuke FUJITA and Masahiro NOTOYA

Morphological and ecological characters. Bot. Bull. Ishikawa Pref. Fish. Res. Cent. 1980; 9: Mag. 1933; 47: 842-862. 135-144 (in Japanese). Morita K, Hamabata M, Masuhara H, Fukase K, Takahashi K, Baba K, Kaneko T, Monma H, Kawasaki Y. Zostera (eelgrass) bed restora- Kurata M, Kuwahara Y, Suzuki T. Amamo. tion in Japan. Fish. Sci. 2002; 68 (Supple- Bull. Hokkaido Pref. Abashiri Fish. Exp. ment II): 1771-1774. Stn. 1997; 203-219 (in Japanese). Nakaoka M, Aioi K. Ecology of seagrasses Tanaka T, Nozawa K, Nozawa Y. The distri- Zostera spp. (Zosteraceae) in Japanese wa- bution of sea-grasses in Japan. Acta Phy- ters: A review. Otsuchi Mar. Sci. Cent. Rep. totax. Geobot. 1962; 20: 180-183 (in Japa- 2001; 26, 7-22. nese). Notoya M, Aruga Y. Vertical distribution and Tanaka N, Kuo J, Omori Y, Nakaoka M, Aioi standing crop of seaweeds, seagrasses, sea K. Phylogenetic relationships in the genera urchins and the spiny top shell along the Zostera and Heterozostera (Zosteraceae) based coasts from Tappi to Fujishima, Tsugaru on matK sequence data. J. Plant. Res. 2003; Peninsula, Aomori Prefecture. Nippon Su- 116: 273-279. isan Gakkaishi. 1992; 58: 885-889. Taniguchi K, Yamada Y. Vertical distribution Ogawa H. The resources and cultivation of sea- and natural life history of Zostera marina weeds. Monographs on aquaculture science Linne and some other species of sea-grass Vol. 10, Midori Shobou, Tokyo. 1987; 230-246 in Iida Bay of the Noto Peninsula on the Omori Y. Zosteraceous species endemic to Ja- Honshu, Japan Sea coast. Bull. Jap. Sea Reg. pan. Bull. Water Plant Soc. Japan 1993; 51: Res. Lab. 1979; 30: 111-122. 19-25 (in Japanese). The Japanese Institute of Technology on Fish Omori Y. Seasonal changes of the productive Port and Communities. Research report on shoot of Zostera caulescens (Zosteraceae) deepwater wave on the coasts of Aomori in Sagami Bay, central Japan. Sci. Rep. Prefecture, The Japanese Institute of Tech- Yokosuka City Mus. 1994; 42: 65-69 (in nology on Fish Port and Communities, Japanese). Tokyo. 1984-1988. Omori Y. Japanese seagrasses - distribution and Wentworth, CK. A scale of grade and class morphology. Aquabiology 2000; 131: 524-532 terms for clastic sediment. J. Geol. 1922; 30: (in Japanese). 377-392. OmoriY,AioiK.Rhizomemorphologyand Yabe T, Ikusima I, Tsuchiya T. Production and branching pattern in Zostera caespitosa Miki population ecology of Phyllospadix iwatensis (Zosteraceae). Otsuchi Mar. Sci. Cent. Rep. Makino. II. Comparative studies on leaf 1998; 23: 49-55 (in Japanese). characteristics, foliage structure and bio- Omori Y, Aioi K. Seasonal changes of the erect mass change in an intertidal and subtidal shoot of Zostera caulescens Miki (Zosteraceae) zone. Ecol. Res. 1996; 11: 291-297. in Sanriku Kaigan, northern Honshu. Sci. Rept. Yokosuka City Mus. 2000; 47: 67-72 (in Received 11 July 2011 Japanese). Accepted 25 June 2013 Tajima M, Sano O. Field research on eelgrass.

12 Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan

青森県沿岸におけるアマモ科植物の分布

桐原慎二・今 男人・藤田大介・能登谷正浩

要 旨

地勢及び海流から日本海，陸奥湾，津軽海峡，太平洋の４つの海域に区分される青森県沿岸 において，1999年から2002年にかけて，海岸線沿いに500ｍ間隔で設けた調査線上の水深2.5ｍ （1,079地点），5ｍ（ 1,181地点）及び10ｍ（ 1,183地点）で潜水し，アマモ科植物の現存量及び生 育地点の砂泥層の厚さと中央粒径値を求めた。この結果，４種のアマモ科植物が採取され，ス ガモは陸奥湾を除く海域の岩盤に認められた。他の３種は砂泥域に生育し，スゲアマモは陸奥 湾と津軽海峡，タチアマモは津軽海峡水深10ｍ，アマモは太平洋以外の海域に認められた。ア マモとスゲアマモは陸奥湾で広範な群落を形成していたが，稀にしか混生せず，スゲアマモは アマモより深所で堆積層が薄く粒度の粗い海底に生育する傾向が認められた。

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