瀬戸内海西部の屋代島，平郡島における海藻藻場の特性 : 特にホンダワラ類とクロメの垂直分布について

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

Yoshida Goro

Shimabukuro Hiromori

Moriguchi Akihiko

Hori Masakazu

Hamaoka Hideki

Takada Shigehiro

Tainaka Tsuyoshi

Kato Aki

生物圏科学 : 広島大学大学院生物圏科学研究科紀要

Journal of the Graduate School of Biosphere Science, Hiroshima University

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.

瀬戸内海

海藻藻場

ホンダワラ類

クロメ

垂直分布

Seto Inland Sea

macroalgal vegetation

sargassaceous plants

Ecklonia kurome

vertical distribution

Biology [ 460 ]

jpn

広島大学大学院生物圏科学研究科

[ISSN] 1348-1371

[NCID] AA11768091

[NAID] 40020370269