平成 18 年度厚岸湖・別寒辺牛湿原学術研究奨励補助研究
調査報告書
海草藻場における一次消費者の群集構造の変動様式の解明とそれに対する魚類群集の応答
千葉大学自然科学研究科
山田勝雅kyamada@graduate.chiba-u.jp【はじめに】
海草藻場は非常に豊富でしかも多様な生物群集を形成し、大型植物（海藻、海草）のみ
ならず、藍藻、珪藻などの微小藻類、原生動物から脊椎動物にいたるまで、海産の殆どすべての動物門に属する動物が出現することが知られる (向井 1993, 相生 1996, 2000, 松政と向井 1996, Zouhiri et al. 1998, 大森 2000, 澤村 2000, 渡辺と仲岡 2000)。また、わが国においては水産資源の産卵場や育成場、水質浄化としての価値が古くから知られている (向井1993, 相生 1996, 2000)。しかしながら近年の埋め立てをはじめ、陸から流入してくる雑排
水による水質汚染などが原因で、草原のようであった大規模な群落は衰退し、現在はパッチ状の小規模な海藻群落になってしまっているものも少なくない (向井 1996, 仲岡 2000)。
海草藻場に生息する生物の生態的な知見の蓄積は、そこに形成されている生態系の構造と機能を評価する上で不可欠であり、特に海草藻場の衰退が危惧される今日においては急務であると考えられる。
北海道厚岸湖内には海草藻場が広い範囲にわたって形成されている。厚岸湖において周年にわたり行われた曳網調査によって採集された試料より 20 属 38 種の端脚類 (Amphipoda)、
7 属 9 種のアミ類 (Mysidacea)、5 属 5 種のクマ類 (Cumacea)、5 属 5 種の等脚類 (Isopoda)、
4 属の十脚類 (Decapoda)、4 属の橈脚類 (Copepoda)をはじめ介形類 (Ostracoda)、毛顎動物(Chaetognatha)、腹足類 (Gastropoda)、刺胞動物 (Cnidaria)、線形動物 (Nemathelminthes)、貧毛類 (Oligochaeta)、多毛類 (Polychaeta)、魚類 (Pisces) などが同定され、厚岸湖で多様な生物相が形成されていることが示されている (Vallet ら 未発表)。なかでも、採集された総個体数に対しアミ類が 77.2％を占めている (Yamada et al., 2007)。アミ類は植物から動物プラ
ンクトン、あるいはデトライタスにいたる多彩な餌を摂餌して成長・増殖する雑食性動物であると認識される (Mauchline 1980)。なかでも閉鎖水域においては、アミによる捕食がプ
ランクトンの群集構造に影響を及ぼすことが指摘されている (e.g. Murtaugh 1981, Siegfried
1982, Wooldridge and Webb 1988, Hanazato 1990, Chigbu and Sibley 1994, Aaser et al. 1995)。
これらアミ類は北海道厚岸湖において、コマイ (Eliginus grocilis)、ハタハタ (Arctoscopus

1japonicus)、エゾアイナメ (Hexagrammos steller)、イソバテング (Blepsias cirrhosus)、ガジ(Opisthocentrus cellatus)などさまざまな魚類の主要な餌料となっており、湖内に出現する 32
種類の魚類の胃内容物には、アミ類が平均重量で 43％を占めていることが報告されている(Watanabe et al., 1995)。平成 16 年度厚岸湖・別寒辺牛湿原学術研究奨励補助制度の一環として行われた厚岸湖の全生物相の調査から (山田, 2005: 平成 16 年度学術研究奨励補助研究報
告書)、厚岸湖内に生息する 100mm 以上に成長する比較的大型の魚類のなかで、シモフリカ
ジ カ Myoxocephalus brandti (Steindachner, 1867) 、ム ロ ラン ギン ポ Pholidapus dybowskii(Steindachner, 1880)、タケギンポ Pholis crassispina (Temminck and Schlegel, 1845)の 3 種が湖内の大型魚類の 9 割以上を占めていたことが報告されている (山田 2006)。
シモフリカジカは漁業対象魚種として知られ、日本近海では、北海道の沿岸域の岩場や藻場に生息しており、体長 35cm ほどに成長することが知られる (渡辺ら, 1996)。一方で、ムロランギンポ、タケギンポは漁業対象種ではなく、藻場（海草場）においてしばしば採集されることが報告されており、ハビタットである海草と密接な関係 (association)を有していることが知られる。渡辺ら (1996) はこれら 3 種を含める厚岸湖に出現する魚類すべての胃内容物調査を行い、食性によって６グループに分類されることを示唆している。一方で、一般的に魚類は成長にともない食性を変化させることが知られ、5cm 程度の大きさであれば、種にかかわりなく類似した食性を示すことも報告されている（体長・gape size 依存型の捕食様式）(渡辺ら, 1996)。
厚岸湖において、餌である一次消費者と魚類は季節、場所によって劇的に変化する (例えば, 山田, 2005: 平成 16 年度学術研究奨励補助研究報告書, 堀ら 2005, 山田ら 2005, Yamada
et al., 2007)。一次消費者であれば、季節的な水温変化に依存した再生産周期の違いによって各種の生物量が変化すると共に (山田 2006, Yamada et al., 2007)、別寒辺牛川から淡水が流入する河口から真龍へと続くに環境要因の著しい変化（勾配）は生物相に変化をもたらすだろう。これら一次消費者の種組成、生物量の時空間変動にともなって、一次消費者を餌とする魚種の分布や生物量も変化すると考えられる。さらに厚岸湖内に繁茂するハビタッ
トとしての海草の有無も生息場所の変化に影響を与えることが予想される。これら複合的な生物的・非生物的要因を解明するためには、一次消費者の生物相の定量的な調査、魚種の各成長段階での食性の解明など、基礎的な知見を蓄積させ、段階的に評価する必要がある。
本報告書では特に、厚岸湖に優占する魚類 3 種、シモフリカジカ、ムロランギンポ、タケギンポの定量採集の結果と、成長段階（体サイズ）にともなう食性の変化について報告する。また、餌である一次消費者動物群集の時空間的変動および海草場の存在が優占する 3
種の生物量や生息域の変化に与える影響について考察する。なお、餌である一次消費者動物群集の時空間的変動様式については (山田, 2005: 平成 16 年度学術研究奨励補助研究報告書)、報告書末尾に添付する別紙を参照とする (英文：以下 Yamada et al., submitted として引用)。

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【材料と方法】
採集は、厚岸湖内 4 定点および湖外の 2 定点において (Yamada et al., submitted 参照)、2006
年 7 月～12007 年 3 月に不定期に行われた。採集は高さ 40 ㎝、幅 50 ㎝、網目幅 500μm のそりネットを用いた。ネットの曳網時間は 3 分とし、 GPS（Global positioning system）によって記録されたネットの投入、揚収地点から曳網距離を求めた。
得られた試料、および 2004-2005 に採集された試料から、優占種 3 種を同定、計数し、各個体の体サイズを測定した。サイズクラス頻度分布を作成後、各サイズクラスからランダムに個体を選出し、胃内容調査に用いた。
胃内容物の充填度は目視によって 1-10 段階で評価した。出現した一次消費者は、同定、計数を行った後、各種について point method を用いての胃内容物に占める貢献度 [Volume
基準 (%)]の評価を行った (Hynes, 1950; Hyslop, 1980)。また、胃内容にみられた各個体については体サイズを測定した。魚類の消化により破損した甲殻類の個体の全長を測定するには、以下の回帰式を使用した (Yamada et al., unpublished)。
Heptacarpus grebnitzkii: TBL = 2.760 CL + 8.921 (R2 = 0.8056, N = 61)
Pandalopsis pacifica: TBL = 2.962 CL + 13.293 (R2 = 0.8680, N = 113)
Crangon sp.: TBL = 4.095 CL + 4.798 (R2 = 0.9654, N = 42),
Acanthomysis shrenckii: Telson L = 0.163 TBL + 0.0556 (R2 = 0.6531, N = 117)
ここで、TBL は全長、CL は背甲長、TL は尾節長を示している。この回帰式により、摂餌された際の餌個体の体長の評価が可能になる。
また、室内実験において、アミ類、その他の甲殻類の被食率の実験を行った。しかし、実験が未完了のため、本報告書では割愛する。
【結果と考察】1. 優占種 3 種ともに、体サイズと共に餌サイズの幅が増加する傾向が見られた (Fig. 1)
2. 3 種の摂餌する餌サイズと体サイズの関係を比較したところ、3 種は成長に伴い異なる
餌サイズを摂餌している傾向が見られた (Fig. 2)。このことは 3 種が厚岸湖内で共存できる理由のひとつかもしれない。
3. 体長に対する餌サイズの割合の変動は、3 種間で異なっていた (Fig. 3)。このことは、3種の摂餌戦略が異なっていることを示唆している。具体的には① シモフリカジカ：体サイズと共に餌サイズは一定になった (Fig. 3a)。このことは、成熟とともに大型の餌のみを獲得し、効率的に摂餌を行っていることが示唆される。
② ムロランギンポ：体サイズと共に餌サイズの幅は増加する (Fig. 3b)。このことは、成熟とともに摂餌可能な餌サイズの幅が増加し、様々なサイズや種を摂餌すること

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で効率的に摂餌を行っていることが示唆される。
③ タケギンポ：体サイズと共に餌サイズに変化は見られなかった (Fig. 3c)。このことは、タケギンポが高い餌獲得能力や戦略を有していることを示している。
④ ①～③のように摂餌戦略が異なることで 3 種の共存が可能となっているのかもしれない。
4. シモフリカジカが体長の約 5%の大きさの餌を摂餌するのに対し、ムロランギンポ、タケギンポは約 2％の大きさの餌を摂餌していた (Fig. 4)。このことは、gape サイズによって餌サイズの幅が決定されていることが示唆され、餌サイズの食べ分けを行うメカニ
ズムのひとつと考えられる。
5. 春、幼魚の出現頻度がもっとも高かった (Fig. 5)。このことは、3 種にとって、春厚岸湖の特に河口域の海草場が幼魚の育成場として利用されていることを示唆している。
6. 分類群で見ると、3 種はサイズ変化に伴って食性を変化させていた (Fig. 5)。けれども、その変化に規則性は見られなかった。
7. Yamada et al., (submitted)をもとに、一次消費者を生息場基準で分類した機能群に分類したところ、体サイズに伴って摂餌する機能群が変化する傾向が見られた (Fig. 6)。このことは 3 種が餌グループを食い分けをしていることを示唆している。
8. 体長と共に変化する機能群の割合についてロジット回帰を行った結果 3 種は異なる傾向を示した (Fig. 7)。具体的には① シモフリカジカ：体サイズと共に、エビ類、魚類を摂餌する割合が増加する。
② ムロランギンポ：小型サイズ時にはカイアシ類や小型のアミ類を摂餌しているが成長に伴い、海草の葉の表面に定着するヨコエビ類や等脚類を摂餌するようになる。
けれども、アミ類はどの体サイズにおいても重要な餌料となっている。
③ タケギンポ：小型サイズ時には小型のアミ類を摂餌するが、成長に伴い、海草の葉の表面に定着するヨコエビ類、ワレカラ類、等脚類を摂餌するようになり、成体になると殆どアミ類を摂餌しない。
④ ①～③は 3 種が餌種を食べ分ける共存機構と考えられる。
9. 各定点において採集された 3 種の胃内容物組成 (V%の平均値)の変化から、タケギンポ
は海草の有無によって食性が著しくことなる一方で、シモフリカジカとムロランギンポには著しい変化は見られなかった。このことは、特にタケギンポは海草との association
が強いことで餌種を食べ分けていることが示唆される (Fig. 8)。
厚岸湖における一次消費者動物群集は、季節的に有意に生物相（多様性・生物量・種組成）が変化すると共に、河口から海洋にかけての塩分勾配に伴って生物相が規則的に変化することが前回の報告書からさらに解析を進めた結果明らかになった (Yamada et al.,submitted)。一方で魚類の胃内容物に同様の傾向は認められなかった。このことは、3 種の魚類が厚岸湖内外の移動を頻繁に行っていることを示唆しており、生活史を示すサイズ分

4布図と矛盾しない (Fig. 5)。
以上のことから厚岸湖に優占する魚類 3 種は、移動、餌サイズの食べわけ、餌グループの食べ分けを効率的に行うことで 3 種は共存を果たしていることが示唆された。このことは逆に、3 種が厚岸湖に生息する一次消費者の各種の生物量をバランスよく間引きすることによって、海草、付着藻類、一次消費者、魚類という低次栄養段階から高次栄養段階への流れを円滑にし、厚岸湖生態系の維持に重要な役割を果たしていることが示唆される (長谷川 2006 も参照)。漁業活動によってカジカなどの種を過剰に漁獲すると、カジカが摂餌している一次消費者の種やグループが著しく増加すると考えられ、厚岸湖生態系が変化する
ことは十分に考えられる。
今後、餌獲得をどのように行っているか、個体間が干渉するような状態になったとき、どのような要因で餌獲得種が決定されるかを室内実験によって解明することでより詳細な
餌の食べ分けの機構が明らかになるだろう。
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Fig.6. Stomach contents of three dominant fish species in Akkeshi-ko estuary. Preyorganisms were classified into taxonomy.

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Fig.7. Stomach contents of three dominant fish species in Akkeshi-ko estuary. Preyorganisms were classified into functional group.

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Fig.7. Variation of stomach contents with growth stage (body length) three dominantfish species in Akkeshi-ko estuary. Prey organisms were classified into functionalgroup.

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Fig. 8. Results of MDS plots showing similarity of community structure in stomach
contents of three dominant fishes in different sites.

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添付書類
Yamada et al., submitted

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Temporal and spatial macrofaunal community changes along a salinity gradient inseagrass meadows of Akkeshi-ko estuary and Akkeshi Bay, northern Japan
Katsumasa YAMADA**Graduate School of Science and Technology, Chiba University, 1-33 Yayoi-cho, Inage, Chiba
263-8522, Japan
Tel.: +81-43-2903929, Fax: +81-43-2903929
E-mail address: kyamada@graduate.chiba-u.jp
Keywords: Macrofauna; Community structure; Salinity gradient; Zostera spp.; Northern Pacific coast.

Abstract
Temporal and spatial variation of the macrofaunal community was investigated in seagrassmeadows in Akkeshi-ko estuary and coastal area of Akkeshi Bay, northern Japan. We specificallyaddressed the question of how the salinity gradient in seagrass meadows affects the species richness,abundance and similarity of faunal groups classified based on the degree of association with theseagrasses, i.e. highly motile species that drift in the water column among seagrass blades(drift-fauna, DF group) and less motile species that are tightly associated with seagrass substrates(seagrass-associated fauna, SA group). A total of 70 species were collected semi-quantitatively using
an epibenthic sledge, among which more than one third of the species were captured in all areas, anda quarter of species only in the marine area. Significant spatial variation in species richness, as well
as a positive relationship between salinity and species richness was found for most samplingoccasions and for both functional groups. Whereas, relationship between salinity and abundance ofmacrofauna was not clear although significant time and site interactions were found for both
functional groups. Patterns of similarity of assemblages varied between the functional groups: clear
differences by sampling sites were discerned for DF group but not for SA group. These results
provided evidence that the macrofaunal community structures in seagrass beds varied with the salinity gradient,but the pattern differed with time and between functional groups, possibly due to the effect of biotic and abiotic
factors that also changed with salinity.

factors have been ascribed to be responsible forthe observed variation in epifauna associated toseagrass beds, including abiotic factors such as
salinity (Edgar & Barrett, 2002), depth (Gambi
et al., 1992), periodic anoxia (Diaz &Rosenberg, 1995) and biotic factors such as
species composition and morphologicalvariation (Nakaoka et al., 2001) as well ascompetition and predator-prey interactions
among animals (Orth et al., 1984; Edgar &Introduction
Seagrass generally enhances thefaunal diversity by increasing habitat
complexity, providing living space and shelter
for a great variety of animal species (Lewis,
1987; Edgar et al., 1994; Jernakoff et al., 1996).
However, the degree to which seagrass
contributes to enhanced faunal abundance anddiversity varies among sites and studies(Hemminga & Duarte, 2000). Numerous17

on the eastern coast of Hokkaido, Japan. We
examined how univariate and multivariate
variables representing abundance, diversity andbetween-site similarity ofmacrofaunal
community vary with different salinity levels.
The patterns of variation were compared
between species with different seagrass
association degree, i.e. between highly motile
species that mostly drift water column among
seagrass blades (drift-fauna, DF group) and lessmotile species that are tightly associated withseagrass substrates (seagrass-associated fauna,
SA group).

Aoki, 1993).
Seagrass beds develop in coastal
areas of broad environmental gradients, and areoften subjected to strong environmental
fluctuations, especially of salinity. A temperate
seagrass, Zostera marina, grows within asalinity range of 5-42 (van Katwijk et al., 1999).
Salinity gradient, i.e. spatial variation in
average and temporal fluctuation in salinity, hasbeen thought to play an important role indetermining
thecomposition
ofthemacrofaunal community in estuaries (e.g., Day,
1981; Williams et al., 1990; Smith & Witman,1999). Lower salinity generally lead to lessspecies diversity and higher individual
abundance (e.g., Remane & Schlieper, 1971;
Montagna & Kalke, 1992; Mannino &Montagna, 1997; Ysebaert et al., 1998; 2003).
Most of these studies were conducted atunvegetated sand flat and mud bottom areas,
whereas fewer studies have investigated theeffects of salinity gradient on faunal
community in seagrass meadows (Montague &Ley, 1993; Schlacher & Wooldridge, 1996;
Edgar & Barrett, 2002).
Although a greater variety of benthic
species inhabit seagrass meadows (Kikuchi,
1966; Hemminga & Duarte, 2000), theirassociation degree with seagrass varies among
species and taxonomic groups. For example,
some amphipods such as Caprella spp. andAmpithoe spp. firmly attach to seagrass blades,
whereas motile species such as mysids andshrimps mostly drift in the spaces between
seagrass shoots and only occasionally attach toseagrass blades. The effect of salinity and otherenvironmental variables within seagrass meadows

Materials and Methods
Study area
Akkeshi-ko estuary is located in theeastern part of Hokkaido, northern Japan (Fig.
1). It is connected to Akkeshi Bay by a narrow
channel (ca. 500 m wide). The south of
Akkeshi Bay is open to the Pacific Ocean. The
surface area of the estuary and Akkeshi Bay is
32 and 110 km2, respectively. Water depth in
the most part of Akkeshi-ko estuary is between
0.8-1.7 m (Iizumi et al., 1995; Yamada et al.,2007), with a maximum of 10 m near thechannel. Three rivers (Bekanbeushi, Tokitai and
Tobai Rivers) flow into the estuary.
Bekanbeushi River has the largest catchment
area, accounting for 98.8 % of the total outfall
to Akkeshi-ko estuary. Its average daily outfall
accounting for 5.8 % of total volume of the
Akkeshi-ko estuary (Iizumi et al., 1995). The
flow input from Bekanbeushi River varied from34 m3 s-1 (flood tide) to 42 m3 s-1 (ebb tide) in
May and from 6 m3 s-1 to 13 m3 s-1 in October(Hasegawa, 2006).
A major part of Akkeshi-ko estuary iscovered with two species of Zostera seagrasses;
Zostera marina covers a wide range of subtidal
area and Z. japonica occurs at the intertidal
zones of the estuary, except for unvegetatedbottoms near of the channel (deepest area in
Akkeshi-ko estuary: mean 5.4 m, Yamada et al.,2007), the mouth of Bekanbeushi River flowing,
and cultivation ground for clam (Ruditapes

may operate differently in the presence of a different
macrofaunal association degree or motile ability,
leading to a different community structure.

This study aims at examining
temporal and spatial variations of themacrofaunal community along a salinity
gradient in a seagrass meadow from the innerpart of the estuary to the sea coast of
Akkeshi-ko estuary and Akkeshi Bay, located18biomass of Z. marina collected in the same
period with this study varied between 28-135 g
DW m-2 at Stn. B, 75-242 g DW m-2 at Stn. C
and 99-200 g DW m-2 at Stn. D (Hasegawa,
2006; Hasegawa et al., 2007). Monthly averagebiomass of Z. marina and Z. asiatica at Stn. F
varied between 182-470 g DW m-2 and 234-903
g DW m-2, respectively (cf. Watanabe et al.,2005). Seagrass biomass at Stn. E was notmeasuredquantitatively
althoughtheabundance of Z. marina and Z. asiatica wassimilar to that at Stn. F (Nakaoka, M., personalobservation).
Salinity at the six stations wasmeasured in June 2004, the same period withthis study, at every 0.5 m above the bottom by T-S
meter (ACT2-D, Alec. Elec. Co.). Such snapshot
samplings of salinity may not represent actual
salinity gradient of these sites because salinity
is subject to change widely with tide andsporadic inflow of river water after heavy rain.
We therefore collected previous data on salinityfrom all available sources that have beenmeasured in June, September and November of
1993, 1997, 2001 and 2005 (Iizumi et al., 1995;
Watanabe et al., 2005; Yamada et al., 2007;
Tanaka et al., unpublished).

philippinarum) and oyster (Crassostera gigas)
that occur scattered in shallow areas of
Akkeshi-ko estuary (Kasim & Mukai, 2006).
Three seagrass species occur in
Akkeshi Bay. Zostera asiatica, an endemic
species to Japan and Korea, is dominant,occurring from the intertidal zone to thedeepest edge (5 m below MLW) of the subtidal
parts of seagrass bed (Watanabe et al., 2005).
Distribution of Z. marina and the surfgrass
Phyllospadix iwatensis is restricted to theshallower edge of the bed (intertidal zone to < 2m deep); they occur in small patches on sandy
and rocky substrata, respectively (Hamamoto &Mukai, 1999; Hasegawa et al., 2005; Watanabe
et al., 2005; Sasil-Orbita & Mukai, 2006).
In the present study, six stations
were established for the temporal collection ofmacrofauna. Stn. A was mainly covered by the
muddy bottom (with a depth of 0.8 m) near themouth of Bekanbeushi River. This station was
unvegetated although a few patches of Z.
marina (1-4 shoot/patch) have been observed
occasionally (Yamada, K. & N. Hasegawa,
personal observation). We neverthelessincluded this station in the present study
because some motile species such as mysid andshrimp were observed to occur abundantly here
(Yamada et al., 2007). Stns. B, C and D werelocated in Z. marina beds; near the river mouth(Stn. B, with the depth of 0.9 m), in the center(Stn. C, 1.5 m) and in the southern part of theestuary (Stn. D, 1.1 m). Stns. E and F werelocated in the seagrass beds at Akkeshi Bay,near the channel connecting the estuary andAkkeshi Bay (Stn. E, with the depth of 1.7 m)
and along the northern coast at ca. 6 km indistance from the estuary (Stn. F, 2.0 m). The
sites within Akkeshi-ko estuary (Stns. A-D) andStn. E in Akkeshi Bay were the same as thosedescribed by Iizumi et al. (1995), Oshima et al.
(1999), Hasegawa (2006) and Yamada et al.
(2007); Stn. F by Hamamoto & Mukai (1999),
Watanabe et al. (2005) and Sasil-Orbita &Mukai (2006).
Monthly mean aboveground

Sampling procedure
The macrofauna sampling in thewater column was carried out at three temporalterms in 2004 (spring: 8-12 June; summer: 2-6
September; autumn: 18-22 November) but not in
winter because the estuary was covered by ice. In
the study areas, at each sampling campaign, three
replicates were collected using an epibenthic

sledge (40 cm height, 60 cm width, 500 µmmesh). The sledge was towed horizontally for
40 m distance (ca. 3 min, 0.5-1.0 m s-1). Actual
distance of each tow was measured using a
GPS plotter (JLU-128, JRC). Great care waspaid when towing the sledge so that it did not
overturn, and that the net was not clogged byseagrass leaves and other debris. Although theepibenthic sledge collects macrofauna withlarge amount of seagrass leaves it does not

19

Mukai (1990), Komai (1999) and Tayasu et al.
(1999) for the shrimps.
Almost all amphipod species werecategorized according to Sawamura (2000) who
investigated the microhabitat and feeding typeof all faunal species captured in a surfgrass(Phyllospadix iwatensis) bed in western
Hokkaido. Sawamura (2000) categorized
gammarid species (ca. 100 species) into 11
groups (borer, commensal, epi-infaunal,
epifaunal, infaunal, interstitial, pelagic, phreatic,
periphytic, streams and terrestrial). In this study,
24 species of gammarid described by
Sawamura (2000) were collected that belonged
to the 11 groups. All species in the epi-infaunal,
epifaunal and periphytic groups were firstclassified to SA group, except for somegammarid amphipods such as Pontogeneia
rostrata and Corophium spp. that have beenreported empirically less firmly attached toseagrass blades (e.g., Crawford, 1937; Pelegri
et al., 1994; Yu et al., 1999; Saigusa et al.,2000). All caprellid species (9 species)
categorized into periphytic groups by
Sawamura (2000) were classified to SA group.

contain all seagrass in the towing area (cf.
McNeill & Bell, 1992). Therefore, themacrofaunal sampling is not totally quantitative
but rather regarded as semi-quantitative, withmacrofaunal species associated tightly withseagrass(i.e.,
SA
group)
possibly
underestimated.
On the whole, 54 samples werecollected during the daytime at mid tide inorder to minimize the effect of tidal flow.
Samples were preserved in 10 % formalinseawater. In the laboratory, samples were
washed and seagrass leaves were removed.
They were then carefully washed again using 1
mm sieves to remove other debris. Thus, theabundance of macrofauna smaller than 1 mm insize may possibly be underestimated. Collected
macrofauna was first classified to 6 taxonomic
groups (shrimp, gastropod, amphipod, isopod,
tanaid and mysid), and then to species. The
number of individuals were counted for eachspecies. Polychaetes were also captured insome samples although data of polychaetes
were not used in the present study because they
were not identified to species due to very small
size (consisting only of juveniles).

The functional grouping of some species that were
not described in Sawamura (2000) or identified tothe species level (but genus level) was made byMacrofaunal grouping
Identified macrofaunal species werecategorized into two groups, drift-faunal group(DF) and seagrass-associated group (SA). DF
consisted of highly motile species that mostly
drift in the water column among seagrasses andrarely attached to seagrass blades, whereas SA
is a group of epifauna firmly attached toseagrass substrates. The classification of eachspecies to the two groups was carried out basedon available information on behavior of eachtaxon. All mysid and shrimp species wereclassified to DF according to references(Mauchline, 1980; Miyake, 1982). Detailed
information for behavior of each species
occurred in this study area were referred also
by Murano (1963), Zelickman (1974), Ohtsuka
et al. (1995) and Yamada et al. (2007) for the
mysids and Yamashita and Hayashi (1984),

information on the congeneric species given in
Sawamura (2000).
All isopod and tanaid species wereclassified into SA group referred by Mukai(1971), Oishi & Saigusa (1999), Saigusa et al.
(2000), and Nakaoka (2003). Three gastropod
species classified into SA group according to
Toyohara et al. (1999) (for Lirularia iridescens)
and Kanamori et al. (2004) (for Lacunadecorata and L. uchidai). For other species
without literature information about association
with seagrass blades (isopod: Paranthurajaponica and Idotea sp., and gastropod:
Barleeia
angustata,
Temanellaturrita,
Batillaria
multiformis,
Reticunassaacutidentatus, R. fratercula hypolia, Retusa sp.
and Margarites pilsbryi), we examined theirhabitat requirement by observations in an

20

assemblage structure, two-way analysis ofsimilarities (ANOSIM; Clarke, 1993) was thenundertaken using sampling time and site asfactors (Clarke & Warwick, 2001).
Correlation between salinity matrix andsimilarity matrix was tested using the Mantel
test for each season and for each functionalgroup. Salinity matrices were constructed using
the absolute difference in average salinity
between a pair of stations as each element (i.e.,
aij = si - s j , where s i was the averagesalinity at site i). The Mantel test was carriedout using the observed Pearson correlation
coefficient as a test statistic against a
permutation distribution generated by 720
iterations of data (exact permutation
distribution for 6 × 6 matrices). The calculation
was carried out using software ‘zt’ (Bonnet &Van de Peer, 2002).

indoor aquarium tank. Several leaves of Z.
marina collected from Akkeshi-ko estuary wereplanted in a tank (13 l) with running seawater,
and a number of >10 individuals of eachspecies were added. Individual position (either
on seagrass leaves or at other sites) was thenobserved with a hour frequency. In all
examinations, individuals of each species
revealed either of the two alternative behaviors;
to stay exclusively on seagrass leaves or onother substrata. The former species wasclassified to SA group and the latter to DF
group.
Data analysis
Spatial and temporal variation in
species richness and abundance of total
macrofauna and two groups of fauna (SA andDF) were compared by two-way ANOVA using
sampling time and site as fixed factors. To
reduce heterogeneous variance associated withpositive correlation between mean and standard
deviation, abundance data were log (x+1)
transformed prior to the analysis. When asignificant interaction between time and site
was detected, multiple comparisons of meansamong sites was conducted for each time
separately by Tukey’s test using the meansquare of residuals of the original two-way
ANOVA (Day & Quinn, 1989; Quinn &Keough, 2002).

Results
Variation in salinity

Salinity observed at several
occasions between 1993 and 2005 did notdeviate greatly when compared for each stationand season (Table 1). It was slightly higher at Stns.
E and F than at Stns. C and D in the middle part ofthe estuary. Salinity changes in the stations close to
the river outfall (Stns. A and B) displayed also hightemporal variations (Table 1). Therefore, sites

with lower average salinity were subjected togreater fluctuation.

Spatial and temporal similarities on thewhole macrofauna and between the two functionalgroups were graphically depicted using

Diversity of macrofauna
A total of 70 species was collectedat Akkeshi-ko estuary and Akkeshi Bay in threeseasons of 2004 (Table 2). The mean annual
species richness for total macrofauna was 14.6
m-2 (± 1.8 SD). Annual average of species
richness in DF group (9.2 m-2 ± 1.2 SD) was
higher than SA group (5.4 m-2 ± 1.2 SD).
Occurrence patterns of each species
were summarized by grouping six stations tothree areas (mouth of river; Stns. A and B,
center of estuary; Stns. C and D, and marine;
Stns. E and F). A number as high as one third of

non-metric multi-dimensional scaling (MDS)
and the ordination method (Clarke & Gorley,
2001; Clarke & Warwick, 2001) using thesoftware PRIMER-E (ver. 5; Plymouth Marine
Laboratory, UK). Abundance values and thepresence/absence of each macrofaunal species
were used, respectively. The similarity matrix
obtained from the abundance values was calculatedby the Bray-Curtis index with double
square-root-transformed (N 1/4) data, as
recommended by Faith et al. (1987) and Clarke(1993). To test temporal and spatial variation in21

DF group, abundance tended to be higher atStns. A and B than the other sites in spring, andit was higher at Stns. B-D than Stns. A, E and F
in summer. In autumn, abundance at Stns. A
and E was significantly lower than otherstations. For SA group, patterns of spatial
variation differed among seasons, althoughmaximum abundance was observed at Stn. B inall seasons.

species was captured in all the areas (35.7 %)whereas a quarter was recorded in the marine
area (25.7 %). Species whose distribution wasrestricted to the river mouth (Stns. A and B:
2.9 %), and to Akkeshi-ko estuary (Stns. A, B,
C and D: 7.1 %) were very few. Thisoccurrence pattern was similar for both SA and
DF groups.
Spatial and temporal variation in
species richness, as well as interactions
between time and station were significant
except for the spatial variation in DF group(Table 3). In all seasons, the lowest species
richness was observed in the unvegetated site
(Stn. A) in the two faunal groups (Fig. 2).
Between spring and summer, species richness
in Akkeshi Bay (Stns. E and F) was higher thanor similar to that in seagrass sites in the estuary(Stns. C and D) for both macrofaunal groups. In
autumn, species richness was lower at Stn. F
than Stns. C and D for DF group, whereas it
was similar at all stations for SA group (Fig. 2).

Similarity in macrofaunal composition
Variations in similarity using theabundance and presence/absence data weresignificant both among sampling occasions andamong sites for the two faunal (DF and SA)groups, whereas the global R among sites washigher than among sampling times (Table 4).
MDS plots showed different similarity
patterns among the faunal groups and between
the two data sets (abundance data andpresence/absence data) (Fig. 4). MDS plots of
the abundance data for DF group showed clear
separation by sites. In contrast, a plot for SA
group showed greater overlaps among sites.
The presence/absence MDS plot was similar tothat by abundance data for DF group althoughsome sites were less clearly separated fromeach other (e.g., between Stns. C and E of total
macrofauna, and between Stns. A and B of DF
group) (Fig. 4). The SA group plot differed
greatly from DF group because of a higher
overlaps among sites. Regardless of data types
and faunal groups, faunal similarity atunvegetated site (Stn. A) differed greatly fromother seagrass meadow sites in all the analyses
except for the presence/absence data for DF
group where position of Stn. A overlaps greatly
with that of Stn. B.
A significant negative relationship was
detected between the similarity matrix (basedon abundance data) and the salinity differencesamong pairs of six areas for SA group insummer, and for DF group in autumn (Table 5).
For the similarity matrix based on thepresence/absence data, significant negative

Abundance of macrofauna
A total of 222,015 individuals
was collected at Akkeshi-ko estuary andAkkeshi Bay in three temporal terms of 2004. A
gastropod, Barleeia angustata, was mostabundant (Table 2). Two mysid species(Neomysis awatschensis and N. mirabilis) and
two amphipod species (Pontogeneia rostrata
and Caprella mutica) also occurred abundantly.
These five species accounted for more than
90% of the total macrofaunal density.
The annual mean abundance intotal macrofauna, DF and SA group was 4,111
inds. m-2, 2,238 inds. m-2 and 1,874 inds. m-2,
respectively. Variation in abundance among
three replicates samples was generally lower in
DF group than in SA group.
Spatial and temporal variation inabundance, and interaction between time andsite were significant for the two groups (Table3). In all sampling occasions, patterns in spatial
abundance variation was much different
between DF group and SA group (Fig. 3). For

22richness of marine species toward the outer bay
contributed to the observed relationships. In
addition, MDS plots using the presence/absence
data were less clearly separated by sites
compared to those using abundance data,
indicating that spatial variation of community
structure of macrofauna may be caused by thatof relative abundance among species rather
than spatial replacement of the species.
In contrast to species richness, effects ofthe salinity gradient on abundance was notclear in most faunal groups. In addition,
patterns of spatial variation changed withsampling occasions. Most notably in summer,
abundance in seagrass meadows of Akkeshi-ko
estuary (Stns. B-D) was much greater than theunvegetated area (Stn. A) and seagrass beds inmarine area (Akkeshi Bay). This contradicts
with the general tendency observed in theprevious studies that found a trend from lower
faunal abundance in upper estuaries areas tohigher abundance in the more downstream
areas (Schaffner et al., 1987; Montagna &Kalke, 1992; Dauer, 1993; Montague & Ley,
1993; Ysebaert et al., 1998; 2003). Thesestudies have discussed that transported foodand nutrients by river input stimulate primary
production
andconsequently
enhanceabundance, biomass and production of faunal
species in more euhaline areas of the estuaries(e.g., Nixon et al., 1986; Montagna & Yoon,
1991; Heip et al., 1995). In the case of ourstudy area, primary productivity in summer isgreater in seagrass beds than unvegetated areasin Akkeshi-ko estuary (Hasegawa et al., 2007;
Hasegawa, N., unpublished). Productivity isalso considered to be greater in Akkeshi-ko
estuary than in Akkeshi Bay in summer due tohigher summer water temperature and greaterorganic and inorganic input from rivers that aretrapped in Akkeshi-ko estuaries (Oshima et al.,1999). Such factors can contribute to theenhanced abundance of macrofauna in summer
in vegetated areas in Akkeshi-ko estuary. In fact,
a population study on the mysid species(belonging to DF group) has revealed that

correlation with salinity difference was foundfor both animal groups in autumn (Table 5).
Discussion
Macrofaunal community structure inseagrass meadows of Akkeshi-ko estuary andAkkeshi Bay varied greatly among sites.
Variation in salinity was related with somevariables representing abundance and species
richness of macrofauna, and their similarity
among sites. However, the patterns of spatial
variation in the macrofaunal community, as
well as the degree of relatedness with salinity
differed among sampling occasions, and among
functional groups of organisms classified by its
degree of association with seagrass substrates.
These findings suggest that the salinity gradient
plays an important role in the observed
variation of the macrofaunal community
structure in the seagrass meadows, but that its
effects are complex, depending on otherconfounding factors and types of animals.
Species richness generally decreased withsalinity in most faunal groups and in mostoccasions. Similar findings were reported inother estuarine systems where the number ofmacrofaunal species was correlated withsalinity (Montagna & Kalke, 1992; Schlacher& Wooldridge, 1996; Mannino & Montagna,
1997; Edgar et al., 1999; Ysebaert et al., 2003).
In earlier studies, variation in macrofaunal
species composition in estuary system wasdiscussed in relation to osmoregularity capacity,
i.e., marine, brackish and freshwater species. It
has been considered that high correlation
between number of macrofaunal species andsalinity is caused by the replacement of thesegroups (Remane, 1934; Remane & Schlieper,1971). Whereas more recent studies argued thatspecific brackish water fauna do not exit, andthat the salinity gradient in species richness iscaused by the fact that fewer marine species
can inhabit in lower salinities (Barnes, 1989;
Hutchings, 1999). In the present study, few
species were considered as freshwater orbrackish species and increasing species23different
requirements
inestuarine
environments. It is likely that only species witha tolerance to low salinity can inhabit
Akkeshi-ko
estuary
althoughspecies-by-species examination for habitat
requirement and life history traits are necessary
to test this possibility.
Comparison between Stn. A (unvegetatedsite) and Stn. B (in seagrass meadow) provides
information on the effects of seagrass
vegetation on macrofaunal community because
these two sites were subjected to similar
environmental conditions at the river mouth. In
most cases, abundance was lower at theunvegetated site, and MDS plots at theunvegetated site were far away from the othervegetated stations for both faunal groups except
for the presence/absence data of DF group.
This finding is consistent with those in previous
studies showing higher diversity of macrofauna
in seagrass meadows (Lewis, 1987; Edgar et al.,
1994; Jernakoff et al., 1996; Hemminga &Duarte, 2000). We expected differences
between the two sites were more pronounced
for SA group that was more associated withseagrass than DF group. The difference inabundance was much greater for SA group as
expected. However, species richness did notvary significantly for both groups between thetwo sites. This agrees with the general findingsthat most epifauna in seagrass beds exhibit little
host specificity on seagrasses (Jernakoff et al.,
1996; Hemminga & Duarte, 2000; Nakaoka,2005). Some dominant species in SA groupsuch as Caprella mutica and Temanella turrita
were commonly found in other substrate types
such as Sargassum beds and rocky bottoms in
Akkeshi-ko estuary and Akkeshi Bay (Yamada,K. & M. Nakaoka, personal observation).
In conclusion, the present study
demonstrated that macrofaunal community
structures in seagrass beds varied with thesalinity gradient of the Akkeshi-ko estuary andadjacent Akkeshi Bay, and that the pattern of
spatial variation differed among seasons, andbetween functional groups of animals withdominant species like Neomysis awatschensis
and N. mirabilis undergo repeated reproduction
in Akkeshi-ko during summer months, and thatN. czerniawskii migrates into Akkeshi-ko
estuary from Akkeshi Bay in summer (Yamada
et al., 2007). Such reproductive and migratory
behaviors of the dominant species lead to theenhanced abundance of DF group. In spring
and autumn, however, the effects of seagrass
vegetation are not so pronounced due to the lowtemperature (ca. < 12 oC) and small shoot size,and dominant macrofaunal species do notundergo reproduction during these seasons.
Such combined effects of abiotic and biotic
factors have resulted in complex time vs. site
interactions in macrofaunal abundance.
One of the important findings in thepresent study is that patterns of spatial variationin diversity, abundance and similarity varied
between the two functional groups that havedifferent degrees of association with seagrass.
Most notably, patterns of similarity varied
greatly, as shown by more overlaps in sites in
MDS plots for SA group compared to DF group.
These results indicate that the effect of salinity
gradient and other related factors operate
differently on the two types of macrofauna.
Species belonging to DF group can migrate
more easily than SA group according toenvironmental factors such salinity gradientand other biological factors such as competitionand predators. For example, three mysid
species (N. awatschensis, N. mirabilis and N.
czerniawskii) which are dominant species of
DF group have different tolerances to salinity,
and the population of each species change
seasonally with different dispersal pattern
between Akkeshi-ko estuary and Akkeshi Bay(Yamada et al., 2007). A grass shrimp, P.
latirostris has low salinity tolerance, with alower survivorship at salinities below 20 (Chibaet al., 2004), which may explain their absencein the upper part of Akkeshi-ko estuary (Stns. A
and B). On the other hand, large overlaps in
MDS plots for SA group indicate that species
belonging to this group did not specialize to24multivariate analyses of changes incommunity structure. Australian Journal of
Ecology 18: 117-143.
Clarke, K. R. & R. N. Gorley, 2001. Primer v5:
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Clarke, K. R. & R. M. Warwick, 2001. Change
in Marine Communities: An Approach to
Statistical Analysis and Interpretation. 2ndedition: PRIMER-E, Plymouth, 172 pp.
Crawford, G. I., 1937. A review of theamphipod genus Corophium, with notes on
the British species. Journal of the Marine
Biological Association of the United
Kingdom 21: 589-630.
Dauer, D. M., 1993. Biological criteria,
environmental health and estuarine
mcrobenthic community structure. Marine
Pollution Bulletin 26: 249-257.
Day, J. H., 1981. Estuarine ecology, withparticular reference to South Africa, A. A.
Balkema, Rotterdam. 411 pp.
Day, R. W. & G. P. Quinn, 1989. Comparisonsof treatments after an analysis of variancein ecology. Ecological Monographs 59:
433-463.
Diaz, R. J. & R. J. Rosenberg, 1995. Marine
benthic hypoxia; a review of its ecologicaleffects and the behavioral responses ofbenthic macrofauna. Oceanography andMarine Biology: An Annual Review 33:
245-303.
Edgar, G. J. & M. Aoki, 1993. Resource
limitation and fish predation: theirimportance to mobile epifauna associatedwith Japanese Sargassum. Oecologia 95:
122-133.
Edgar, G. J. & N. S. Barrett, 2002. Benthic
macrofauna in Tasmanian estuaries: scalesof distribution and relationships withenvironmental variables. Journal of
Experimental Marine Biology and Ecology
270: 1-24.
Edgar, G. J., N. S. Barrett & P. R. Last, 1999.
The distribution of macroinvertebrates andfishes in Tasmanian estuaries. Journal ofdifferent degree of dependence on seagrass
substrates. However, it remains unknown if theobserved variation along salinity gradient wasdue to direct effects of salinity, or otherbiotic/abiotic factors such as the variation inseagrass biomass, food availability andpredation intensity that can also change withsalinity. Concurrent monitoring of these
unexamined factors as well as experimental
analyses
carefully
manipulating
these
confounding factors are the next step toward
the understanding the underlying mechanisms
causing the variation in macrofaunal
community in seagrass meadows along salinity
gradient.
Acknowledgements
We gratefully thank Captain S.
Hamano, H. Katsuragawa and other staff of the
Akkeshi Marine Station for assistance with thefield collection. H. Mukai, C. Vallet, K.
Takahashi, M. Kanamori, M. Watanabe, N. H.
Kumagai and T. Takano helped with the species
identification, analysis and discussion. M.
Takahata and Y. Ishikawa of the Community
Ecology Laboratory of Chiba University helpedwith the laboratory procedures and contributed
to the fruitful discussions during the course ofthis study. A part of this research was
financially supported by a Grant-in-Aid by
Akkeshi Town for Scientific Research of Lake
Akkeshi and Bekanbeushi Wetland to KY.
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Fig. 1. Study sites at Akkeshi-ko estuary (Stns. A-D) and Akkeshi Bay (Stns. E and F). Shaded areas
indicate vegetation cover of the three Zostera species.

29

Fig. 2. Spatial and temporal variation in species richness of two functional groups (drift-faunal groupand seagrass-associated group) in Akkeshi-ko estuary and Akkeshi Bay. Bars indicate SD of thethree replicated samples. Different letters denote a pair of sites with significant differences detectedusing Tukey post-hoc comparisons.

30

Fig. 3. Spatial and temporal variation in abundance of two functional groups (drift-faunal group andseagrass-associated group) in Akkeshi-ko estuary and Akkeshi Bay. Bars indicate 0.5 SD of
the three replicated samples. Different letters denote a pair of sites with significant
differences detected by Tukey post-hoc comparisons.

31Fig. 4. Results of MDS plots showing similarity of community structure in different sites (Stns. A-F)
and seasons (sp.; spring, su.; summer and au.; autumn) for each faunal group (drift-faunalgroup and seagrass-associated group). Bray-Curtis similarities were calculated based on
double-square root of abundance (Abn.) and the presence/absence of each taxon (P/A) for the
analysis.

32

Table 1. Mean, median values and standard deviation of salinity recorded from 1993 to 2005 at each station of Akkeshi-ko estuary andAkkeshi Bay in each season. Averaged salinity (Bold type) for each season and site was used for analysis of this study due toreducing possible biases of data taken at abnormal conditions.
Stations
SeasonSpringSummerAutumnYear

References
A

B

C

D

E

F

1993

7.7

25.2

24.5

20.4

26.7

-

1997

18.6

27.9

27.0

26.3

29.5

31.8

Yamada et al. (2007)b

2001

-

-

-

-

-

24.0

Watanabe et al. (2005)b

2004

22.7

25.0

26.8

24.5

27.4

28.9

This studyb

2005

-

27.1

29.0

27.0

29.4

-

Average

16.3

26.3

26.8

24.5

28.3

28.2

Median

17.5

26.3

26.8

24.5

28.3

28.6

SD

7.8

1.4

1.8

3.0

1.4

3.9

1993

2.0

11.8

22.8

23.1

25.2

-

1997

10.3

12.7

29.1

26.0

26.9

30.9

Yamada et al. (2007)b

2001

-

-

-

-

-

30.7

Watanabe et al. (2005)b

2005

-

20.9

29.1

26.0

31.0

-

Tanaka et al. (unpubl.)c

Average

6.2

15.1

27.0

25.0

27.7

30.8

Median

6.2

13.9

28.0

25.5

27.3

30.8

SD

5.9

5.0

3.7

1.7

3.0

0.1

1993

26.3

23.5

26.8

25.1

29.3

-

1997

8.3

20.8

29.0

27.9

29.2

32.9

Yamada et al. (2007)b

2001

-

-

-

-

-

33.0

Watanabe et al. (2005)b

2005

16.6

-

28.2

29.9

32.2

32.9

Tanaka et al. (unpubl.)c

Average

13.6

19.8

27.6

26.0

28.7

32.2

Median

15.1

20.8

27.9

26.9

29.2

32.9

SD

9.0

1.9

1.2

2.4

1.8

<0.1

33

Iizumi et al. (1995)a

Tanaka et al. (unpubl.)c

Iizumi et al. (1995)a

Iizumi et al. (1995)atom and surface during the daytime by T-S meter.
b

At every 0.5 m above the bottom during the daytime by T-S meter.

c

At 0.3 m above the bottom in during several days by Alec. COMPACT-CT (every 1-10 min.)Table 2. Occurrence pattern of a total of 70 species among regions in Akkeshi-ko estuary and Akkeshi Bay.
AverageSpeciesRankabundance

Proportion(inds. m-2)(%)

SpatialFaunaltype

occurrence
A B C D E F

Amphipoda
Pontogeneia rostrata

4

369.078.99

DF+ + + + + +Caprella mutica

5

121.60

2.96

SA

+

Ampithoe lacertosa

8

34.53

0.84

SA

+ + +

Grandidierella japonica

9

30.93

0.75

DF

+ + + + + +Corophium acherusicum

10

26.49

0.65

DF

+ + + + +Ischyrocerus anguipes

13

14.89

0.36

SA

+

Caprella penantis (S type)

14

14.61

0.36

SA

Pleustes panopla

17

12.36

0.30

Photis reinhardi

18

8.41

Caprella gigantochir

19

Aoroides columbiae+ + + +

+ +
+

+

SA

+ + +

+

0.20

DF

+

7.78

0.19

SA

+ +

20

7.04

0.17

SA

+ + +

Ampithoe sp.

21

5.49

0.13

SA

+ + + + + +Eogammarus sp.

22

4.61

0.11

DF

+ +

Corphium sp.

24

3.51

0.09

DF

+ +

Hyale sp.

27

2.10

0.05

SA

Caprella kroyeri

28

1.98

0.05

SA

Grandidierella sp.

29

1.48

0.04

DF

Metaphoxus sp.

31

1.42

0.03

DF

+

Synchelidium lenorstalum

33

1.08

0.03

DF

+ + +

Aoroides sp. 1

34

1.04

0.03

SA

Aoroides longimerus

35

0.93

0.02

SA

+

Metopa sp.

37

0.71

0.02

SA

+ + + +

Caprella scaura

38

0.71

0.02

SA

+

Orchomene sp.

40

0.52

0.01

DF

Caprella laeviuscula

41

0.44

0.01

SA

Caprella polyacantha

42

0.36

0.01

SA

34

+ +

+ +

+

+

+ +

+ +

+ +
+

+

+

+

+

+

+

+
+
+

+

+ +

Caprella tsugarensis

43

0.36

0.01

SA

Pleusirus secorrus

44

0.26

0.01

DF

Hyale barbicornis

47

0.12

<0.01

SA

Allorchestes sp.

48

0.09

<0.01

SA

+

Urothoe grimaldii japonica

50

0.06

<0.01

DF

+

Caprella danilevskii

52

0.04

<0.01

SA

+

Caprella bispinosa

53

0.03

<0.01

SA

+

Stenothoe sp.

54

0.03

<0.01

SA

+

Aoroides sp. 2

55

0.02

<0.01

SA

+

Monoculodes sp.

59

0.01

<0.01

DF

+

Byblis japonicus

61

0.01

<0.01

DF

Crangon sp.

11

20.36

0.50

DF

+ + + + + +Spirontocaris ochotensis

23

3.76

0.09

DF

+ + + +

Pandalopsis pacifica

25

3.32

0.08

DF

+

Heptacarpus grebnitzkii

30

1.46

0.04

DF

+ + + + +Heptacarpus rectirostris

45

0.20

<0.01

DF

+ + + + +Pandalus kessleri

46

0.18

<0.01

DF

+

+ +

Eualus leptognathus

51

0.05

<0.01

DF

+

+ +

Heptacarpus sp.

58

0.02

<0.01

DF

Lebbeus speciosus

63

0.01

<0.01

DF

Sergia lucens

66

<0.01

<0.01

DF

+

Barleeia angustata1

1590.45

38.75

SA+ + + + +Temanella turrita

7

34.82

0.85

SA

+ + + + + +Reticunassa acutidentatus

26

2.20

0.05

DF

+ + +

Lacuna decorata

49

0.09

<0.01

SA

+ + + + +Reticunassa fratercula hypolia

56

0.02

<0.01

DF

+

Retusa sp.

57

0.02

<0.01

DF

+

Lirularia iridescens

60

0.02

<0.01

SA

+

Batillaria multiformis

67

<0.01

<0.01

DF

+ +

Lacuna uchidai

69

<0.01

<0.01

SA

+

Margarites pilsbryi

70

<0.01

<0.01

SA

+

+

+
+
+
+

+

Decapoda

+ + +

+ +
+

Gastropoda

35

+ +

MysidaNeomysis awatschensis

2977.7023.80

DF+ + + + +Neomysis mirabilis

3709.0517.27

DF+ + + + +Acanthomysis schrencki

6

36.62

0.89

DF

+

Neomysis czerniawskii

15

14.36

0.35

DF

+ + + +

Exacanthomysis

16

13.26

0.32

DF

+ +

Nipponomysis toriumii

39

0.54

0.01

DF

+

Acanthomysis sp.

64

0.01

0.01

DF

+ +

Cymodoce japonica

12

18.74

0.46

SA

+ + + + + +Idotea ochotensis

32

1.36

0.03

SA

+ + + + + +Paranthura japonica

36

0.82

0.02

SA

+ +

Idotea sp.

62

0.01

<0.01

SA

+

Zeuxo sp.

65

<0.01

<0.01

SA

+

Tecticeps glaber

68

<0.01

<0.01

SA

japonica+ + + +

Isopoda and Tanaida+

Table 3. Results of two-way ANOVA testing spatial and seasonal variation in species richness (number of species m-2) and abundance (logtransformed inds. m-2) of two macrofaunal groups (DF and SA).

Factor

df

MS

F

P

Species richness (number of species m-2)

Factor

df

MS

F

P

Abundance (log transformed inds. m-2)

Drift faunal group

Drift faunal group

Season

2

5.17

1.97

<0.001

Season

2

0.62

8.7

<0.001

Site

5

36.52

13.89

0.155

Site

5

3.47

48.75

0.001

Season × Site

10

8.19

3.11

0.006

Season × Site

10

1.08

15.17

<0.001

Error

36

2.63

Error

36

0.07

36

Seagrass associated group (SA)

Seagrass associated group (SA)

Season

2

66.5

23.94

<0.001

Season

2

4.47

29.54

<0.001

Site

5

40.03

14.41

<0.001

Site

5

3.91

25.83

<0.001

Season × Site

10

11.17

4.02

0.001

Season × Site

10

1.52

10.02

<0.001

Error

36

2.78

Error

36

0.15

Table 4. Results of ANOSIM testing among-season and among-site variations in similarity of two
functional group (DF and SA). The test was carried for similarity data obtained for the two types of data
(abundance and presence/absence).
Faunal group

Among seasons

Among sites

Global R

P

Global R

P

Drift faunal group (DF)0.850

< 0.001

0.956< 0.001

Seagrass associated group (SA)0.508

< 0.001

0.654< 0.001

Drift faunal group (DF)0.567

< 0.001

0.886< 0.001

Seagrass associated group (SA)0.375

< 0.001

0.526< 0.001

Abundance (transformed)

Presence / Absence37

Table 5. Results of Mantel test (r) betweensimilarity matrices of two macrofaunal groups (DFand SA) and differential salinity matrix for pairs of stations.
SpringSummerAutumnFaunal group
r

P

r

P

r

P

Drift faunal group (DF)-0.2350.086-0.1550.267-0.7820.006

Seagrass associated group (SA)

-0.3180.031-0.5720.021-0.441

0.069

Drift faunal group (DF)-0.0140.306-0.431

0.096-0.9020.003

Seagrass associated group (SA)

-0.3120.050-0.5220.143-0.5670.028

Abundance (transformed)

Presence / Absence38