Ecological characteristics of Ecklonia cava ssp. kurome (Laminariales, Phaeophyceae) in the western Seto Inland Sea I. biomass, production rates and morphological diversity

クロメは瀬戸内海中央・西部海域に唯一分布するアラメ・カジメ類であり，藻場の構成種として極めて重要である。本報では2012～13年に瀬戸内海西部（平郡島，片島，屋代島）で調査したクロメの現存量，生産量などの諸元を取りまとめた。優占群落における繁茂期（6～7月）の平均現存量は0.7～1.3kg乾重 m-2であり，成体の平均密度はおおむね10～20個体m-2であった。片島と屋代島・松ヶ鼻において，葉状部のマーキング法で測定した生産量は，繁茂期に10.4～15.6g乾重m-2日-1，衰退期（10～11月）に1.8～5.3g乾重m-2日-1，成長期（2～3月）に5.8～12.9g乾重m-2日-1 であり，本海域のクロメは太平洋や東シナ海のクロメおよび近縁のカジメと同程度の生産力を有していた。繁茂期の成体の茎長や中央葉の長さと幅の比，PPNI値等には調査地間で有意な差異があり，クロメの形態にはそれぞれの生育環境を反映すると推測される多様性がみとめられた。Ecklonia cava ssp. kurome is the only perennial kelp which is distributed in the central and western areas of the Seto Inland Sea, and is an important component of macroalgal beds in these areas. Biomass and production rates of this species were surveyed at three islands (Heigun-jima Is., Kata-shima Is. and Yashiro-jima Is.) in the western Seto Inland Sea during 2012–13. The mean biomass of dominant stands in the luxuriant season (June–July) ranged from 0.7 to 1.3 kg DW m-2 and the mean adult thallus density was approximately in the range of 10–20 inds. m-2. Net production was estimated by the leaf-marking method at Kata-shima Is. and Matsu-ga-hana in Yashiro-jima Is. Estimated production rates were 10.4–15.6 g DW m-2 d-1 in the luxuriant season, 1.8–5.3 g DW m-2 d-1 in the senescent season (October–November), and 5.8–12.9 g DW m-2 d-1 in the growth season (February–March). These trends were similar to those for E. cava ssp. kurome and its closely related E. cava ssp. cava reported in the Pacific Ocean and East China Sea, respectively. Morphological characteristics, such as stipe length, length/width ratio of the central blade and the primary pinna number index (PPNI) of adult E. cava ssp. kurome thalli exhibited significant differences in the luxuriant season among the survey sites, which reflected variable environmental conditions in their habitats.本研究は，水産庁「地球温暖化対策推進費委託事業」のうち「藻場・干潟の炭素吸収源評価と吸収機能向上技術の開発」（平成23，24年度）の一環として実施し， とりまとめにあたってはJSPS科研費18H02268（代表者；吉田吾郎）の助成を受けた

瀬戸内海における株サイズと群落構造の異なるアマモの生産量 : 2012年繁茂期の生産量

2012年６月に瀬戸内海の３つのアマモ場の，それぞれ異なる株サイズと群落構造を示す計7地点のアマモ群落において生産量を測定，比較した。株あたりの生産量は株サイズに依存し，大きい株が相対的に低い密度で生育する生野島（広島県；安芸灘）のアマモ場で50.0-73.2 mg DW shoot -1 d-1であり，小さい株が密生する平郡島（山口県；伊予灘）の株あたり生産量（7.7-27.4 mg DW shoot -1 d-1）より大きかった。面積あたり生産量において，株あたり生産量の差は株密度により相殺される傾向もみられたが，生野島のアマモ場の生産量（2.89-5.38 g DW m-2 d-1）の方が平郡島のアマモ場の生産量(1.63-2.56 g DW m-2 d-1) よりも大きかった。これら２つのアマモ場では底質に大きな相違がみられ，アマモの群落構造や生産量に影響を与えていると考えられた。すなわち，生野島の底質はほとんど泥により構成され有機物含量も高い一方で，平郡島の底質は中砂・細砂を中心に構成されより厳しい波浪環境を反映していた。 2011年秋季のアイゴの食害による消失から回復途上にある阿波島（広島県；安芸灘）のアマモ場では新たに発芽した実生由来の株がパッチ状の群落を作り，株密度も現存量も低かった。調査した群落の中で生産量は最も低かったが(0.60 g DW m-2 d-1)，その現存量回転率（6.5％ d-1）は，他群落（1.7-3.3％ d-1）のそれよりも大きかった。In June 2012, production was measured and compared among Zostera marina stands with different shoot sizes and stand structures, at a total of seven stations in three Z. marina beds in the Seto Inland Sea, Japan. Production per shoot depended on the shoot size, and was larger (50.9 - 73.2 mg DW shoot -1 d-1) at the stands in the bed of Ikuno-shima Is. (Hiroshima Pref.; Aki-Nada Sea), where large shoots formed stands with lower densities, than at stands in the bed of Heigun-jima Is. (Yamaguchi Pref.; Suo-Nada Sea) (7.7 - 27.4 mg DW shoot -1 d-1) where small shoots exhibited higher densities. Though the areal production estimated was compensated by shoot density, it was still larger at the bed of Ikunoshima Is. (2.89-5.38 g DW m-2 d-1) than at Heigun-jima Is. (1.63 - 2.56 g DW m-2 d-1). Sediment characteristics were quite different between the two Z. marina beds and considered to affect the stand structures and productivity, i.e., the sediment at Ikuno-shima Is. was muddy and rich in organic matter and the sediment at Heigun-jima Is. was dominated by sand indicating severer physical conditions induced by waves. In Aba-shima Is. (Hiroshima Pref.; Aki-Nada Sea), the third research site, the Z. marina bed was on the way of recovery after catastrophic damage due to heavy grazing of rabbitfish (Siganus fuscescens) which had occurred in autumn of 2011, and young shoots developed from seeds forming a patchy stand with a low shoot density and biomass. Though the production was lowest (0.60 g DW m-2 d-1), the turnover of the biomass was higher (6.5 % d-1) at the stand in Aba-shima Is. than values (1.7-3.3% d-1) at the other two beds.This study was partially funded by the project of Ministry of Agriculture, Forestry and Fisheries ‘Technology development for circulatory food production systems responsive to climate change’

Characteristics of macroalgal vegetation along the coasts of Yashiro and Heigun islands, western Seto Inland Sea, Japan : especially, on the vertical distribution patterns of species of Sargassum and Ecklonia

瀬戸内海西部の伊予灘と広島湾の島嶼（屋代島，平郡島）で，大型褐藻のホンダワラ類（ヒバマタ目ホンダワラ科）とクロメ（コンブ目レッソニア科）により形成される藻場の特性を調べた。対象とした藻場は，自然岩礁域およびそれに付帯する礫集積域に形成されているものが8か所，投石による人工礁に形成されているものが3か所であり，ライントランセクト法により植生の垂直構造を明らかにし，そこにみられる法則性と環境要因との関係について考察した。調査では計85種の海藻を確認し，そのうちホンダワラ類についてはヒジキ，ノコギリモク，アカモク，ジョロモク，ホンダワラ等の計14種をみとめた。総じて，ホンダワラ類は潮間帯から水深4m 程度までで優占し，クロメは14mを下限にホンダワラ類より深所まで分布した。しかし，平郡島南岸や屋代島南岸では，浅所の岩盤上部にクロメ，その下部の漂砂影響域や礫集積域にホンダワラ類が生育し，植生の垂直構造が逆転している場合もみとめられた。人工礁上では，おおむね自然岩礁・礫集積域と類似した植生が形成されていたが，特に屋代島北岸（広島湾側）では深所で沈積浮泥の影響がみとめられ，クロメの生育は不良であるか植生から欠落していた。藻場の環境特性と植生の関係を解析した結果，平均水深が浅い藻場ではホンダワラ類の平均被度が大きくなり，海底傾斜が大きい藻場ではクロメの平均被度が大きくなる傾向がみとめられた。Characteristics of macroalgal beds composed of sargassaceous plants (Fucales, Phaeophyta) and Ecklonia kurome (Laminariales, Phaeophyta) were surveyed at Yashiro and Heigun islands in the western Seto Inland Sea (Iyo-nada Sea and Hiroshima Bay areas). The surveyed macroalgal beds were located on 8 natural rocky or boulder shores and 3 subtidal stone-built artificial reefs. A transect was set at each bed between the upper and lower limits of the macroalgal vegetation to investigate vertical distribution patterns of the constituent species. Eighty-five macroalgal species were recognized in total, and among those, 14 sargassaceous species, such as Sargassum fusiforme, S. macrocarpum, S. horneri, S. fulvellum and Myagropsis myagroides, were found. In general, sargassaceous plants were dominant from the intertidal to 4 m depth, and E. kurome distributed in deeper zones than sargassaceous plants, down to 14 m at the deepest. However, in some beds on the southern coasts of the islands, this vertical pattern was reversed. Ecklonia grows on rocky substrata which was stable and free from the effects of sand action, though sargassaceous plants grow on boulders distributed in zones deeper than the Ecklonia zones. On artificial reefs, similar vegetation with those on natural substrata was established. On reefs of the northern coast of Yashiro Is. (Hiroshima Bay area), however, sedimentation on substrata prevented the growth of Ecklonia. In the correlation analysis between physical characteristics and vegetation of the beds, there is a tendency that mean coverage of sargassaceous plants of the beds is higher as the mean depth of the beds becomes shallower, and that mean coverage of Ecklonia is higher as the slope of the beds becomes steeper.本現地調査は，農林水産省プロジェクト研究「地球温暖化が水産分野に与える影響評価と適応技術の開発」（平成22―24年度）および水産庁「藻場・干潟の炭素吸収源評価と吸収機能向上技術の開発」（平成23，24年度）の一環として実施し，とりまとめにあたってはJSPS科研費25450267の助成を受けたものである

A New Record of Sargassum alternato-pinnatum Yamada (Fucales, Phaeophyceae) from Taiwan

This report describes Sargassum alternato-pinnatum Yamada as a newly recorded species in Taiwan. The specimens for this study were collected from a shallow tidepool in Lan-yu, Taiwan. This species is characterized by the following features: (1) small discoid holdfast, (2) terete primary branches, (3) sharp spines arising from surface of branches, (4) leaves that furcate 1–3 times, (5) spherical vesicles around the apex, (6) pseudozygocarpic receptacles with leaves or vesicle-like tissues, and (7) male and female conceptacles scattered within the receptacles. In this report, we also present a line drawing and photographs for the identification of S. alternato-pinnatum

Development of Quantitative Real-Time PCR for Detecting Environmental DNA Derived from Marine Macrophytes and Its Application to a Field Survey in Hiroshima Bay, Japan

The sequestration and storage of carbon dioxide by marine macrophytes is called blue carbon; this ecosystem function of coastal marine ecosystems constitutes an important countermeasure to global climate change. The contribution of marine macrophytes to blue carbon requires a detailed examination of the organic carbon stock released by these macrophytes. Here, we introduce a quantitative real-time polymerase chain reaction (qPCR)-based environmental DNA (eDNA) system for the species-specific detection of marine macrophytes. and report its application in a field survey in Hiroshima Bay, Japan. A method of qPCR-based quantification was developed for mangrove, seagrass, Phaeophyceae, Rhodophyta and Chlorophyta species, or species-complex, collected from the Japanese coast to investigate their dynamics after they wither and die in the marine environment. A trial of the designed qPCR system was conducted using sediment samples from Hiroshima Bay. Ulva spp. were abundant in coastal areas of the bay, yet their eDNA in the sediments was scarce. In contrast, Zostera marina and the Sargassum subgenus Bactrophycus spp. were found at various sites in the bay, and high amounts of their eDNA were detected in the sediments. These results suggest that the fate of macrophyte-derived organic carbon after death varies among species

Seaweed community structures in the temperate zooxanthellate scleractinian coral Alveopora japonica bed in the western Seto Inland Sea, Japan

有藻性イシサンゴ類のニホンアワサンゴは，台湾から韓国，日本に分布し，近年，海藻藻場での群生が確認されているが，生育地の海藻群落構造はほとんど研究されていない。山口県屋代島は，このサンゴの分布域では最も水温が低いにもかかわらず，2012年に大規模な群生地（1940m2）が確認され，2013年に瀬戸内海国立公園の海域公園に指定された。2014年に，海藻の繁茂期と少ない時期に海藻群落構造の調査を行った。年間を通して，サンゴ被度の高い場所では大型褐藻類の被度が低かったが，群生地の水温は，これらの種の生育適温の範囲内であった。水温上昇以外の局所的な要因により，大型褐藻被度が低下し，群生地が拡大したと考えられる。The zooxanthellate scleractinian coral Alveopora japonica is endemic to the northwestern Pacific, ranging from Taiwan to Korea and Japan. This coral has recently expanded into seaweed beds in the temperate waters of these regions, as the seawater temperature increased. The largest known bed of A. japonica (1940 m2) was found in 2012 at Yashiro Island, in the Seto Inland Sea in the temperate region of Japan, where the minimum seawater temperature is the lowest among the regions inhabited by this coral. We surveyed the coverage of seaweeds and A. japonica in this coral bed during the seaweed-abundant and seaweed-sparse seasons in 2014. Throughout the year, the coverage of Ecklonia kurome and sargassaceous plants was low in places where the coverage of A. japonica was high. The maximum seawater temperature was within the optimal range for the growth of these seaweeds, indicating that the increasing temperature did not adversely affect seaweed growth. Evidently, a local environmental stress rather than the increase in seawater temperature caused the decline of the canopy-forming seaweeds that, in turn, allowed the coral bed to expand. Our research provides baseline data to compare with and analyze future changes at the edge of A. japonica distribution.This research was mainly supported by the Supporting Grant 2014 from the Fujiwara Natural History Foundation, Japan to AK

The role of chemical antifouling defence in the invasion success of Sargassum muticum: A comparison of native and invasive brown algae.

Competition and fouling defence are important traits that may facilitate invasions by non-indigenous species. The 'novel weapons hypothesis' (NWH) predicts that the invasive success of exotic species is closely linked to the possession of chemical defence compounds that the recipient community in the new range is not adapted to. In order to assess whether chemical defence traits contribute to invasion success, anti-bacterial, anti-quorum sensing, anti-diatom, anti-larval and anti-algal properties were investigated for the following algae: a) the invasive brown alga Sargassum muticum from both, its native (Japan) and invasive (Germany) range, b) the two non- or weak invasive species Sargassum fusiforme and Sargassum horneri from Japan, and c) Fucus vesiculosus, a native brown alga from Germany. Crude and surface extracts and lipid fractions of active extracts were tested against common fouling organisms and zygotes of a dominant competing brown alga. Extracts of the native brown alga F. vesiculosus inhibited more bacterial strains (75%) than any of the Sargassum spp. (17 to 29%). However, Sargassum spp. from Japan exhibited the strongest settlement inhibition against the diatom Cylindrotheca closterium, larvae of the bryozoan Bugula neritina and zygotes of the brown alga F. vesiculosus. Overall, extracts of S. muticum from the invasive range were less active compared to those of the native range suggesting an adaptation to lower fouling pressure and competition in the new range resulting in a shift of resource allocation from costly chemical defence to reproduction and growth. Non-invasive Sargassum spp. from Japan was equally defended against fouling and competitors like S. muticum from Japan indicating a necessity to include these species in European monitoring programs. The variable antifouling activity of surface and crude extracts highlights the importance to use both for an initial screening for antifouling activity

Analysis of Floating Macroalgae Distribution around Japan Using Global Change Observation Mission-Climate/Second-Generation Global Imager Data

Floating macroalgae information is required to manage coastal environments and fishery resources effectively. In situ observations and analyses can result in under-sampling, thereby challenging the comprehension of the floating macroalgae abundance and spatiotemporal alterations. This study reports the spatiotemporal variation of floating macroalgae distribution around Japan from 2018 to 2021 using Global Change Observation Mission-Climate/second-generation Global Imager data. We employed the floating algae index (FAI) scaled from local ocean FAI to minimize the effect of spatial variation in ocean color. Fractional macroalgae coverage in a pixel was determined using a linear unmixing algorithm with lower and upper thresholds. The lower threshold was determined using the cumulative frequency of the scaled FAI, and the upper threshold was modified based on the more precise Sentinel-2 data. The results revealed that monthly macroalgae coverage varies spatially and seasonally, peaking in the spring and summer in the southwestern area. The macroalgae distribution particularly expanded from the East China Sea to west Japan during spring. In 2018–2021, the total biomass of the offshore floating macroalgae was estimated to be 8880–133,790, 8460–141,900, 3910–70,380, and 4620–61,870 tons. The findings of this study validated the empirical knowledge about specific locations and can serve as a reference to analyze temporal and spatial variations in future studies