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アラメ・カジメ群落に関する生態学的研究 - III : アラメ藻体における相対生長の季節変化

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Abstract

三重県志摩半島, 岩井崎沿岸のアラメ藻体における相対生長の季節変化を比較・検討し,次の様な結果を得た。 1) アラメの茎長・茎径に対する茎部・葉部および個体重量との間には,それぞれの組合せで明瞭な相対生長関係が成立した。 2)相対生長には不連続性がみられ,分叉を境に2本の回帰式で表わすことができた。この不連続性は,分叉前と分叉後において,形態が大きく変化するためである。 3) 茎長と茎径の関係は,茎径の値に上限値をもつ拡張相対生長式で表わすことができた。 4) アラメの新生群は,発芽後約1年を経た11月頃から翌年3月までの聞に分叉するが,茎の短い一部の個体は,分叉が遅れるものと思われる。 5)生長輪は3ないし4輪まで認められ,各輪群は相対生長の季節変化の中で年級群として明瞭に把握することができた。 6) 生長輪は3月頃から6月までの間に形成されるが,1輪目は新生群の中の茎長の長い個体のみに形成され,茎長の短い個体は形成が遅れる。 7) 生長論,アラメについても,新生群の輪紋形成時期を考慮すれば,年令形質として利用できることが認められた。 8) 茎長は藻体各部との間に相対生長関係が成立することや測定が容易であることなどから,群落構造を解析する基準形質として適切と思われる。

Eisenia bicyclis is widely distributed along the central Pacific coast of Honshu, Japan,and forms a dense marine forest on the rocky bottom. The purpose of the present study was to obtain the primary data for analyzing the structure of the Eisenia population by comparing the seasonal changes in allometry. The materials examined were collected seasonally at a depth of 3m from the coastal area of Goza, around the Shima Peninsula, Mie Prefecture. There is an allometric relation between the length and diameter of stipes and the weight of stipe, blade and fornd, respectivelly. The allometry of Eisenia was discontinuous and, because of the remarkable change in its from about one year after germination when the upper part of the stipe forked, it could be represented by two equations. The equations for stipe weight to stipe length were regular nearly all the year round, and showed a slight discontinuity, but those for blade weight to stipe length varied seasonally and had notable discontinuity. This clearly shows that the seasonal changes in frond weight depend on the changes in blade weight, and that this discontinuity is due to the changes in blade weight when the stipe forks. The relation between stipe length and stipe diameter was represented by extended allometric equations which had the upper limit of stipe diameter. From one to four growth rings were counted among the materials collected, and each ring group was distinguished from the others in the figure of allometry. Generally the growth rings were formed from about March to June, but in young plants the first ring was not formed in fronds with a short stipe of less than 5cm. It seems that except for young plants, the growth ring may be used as an indicator of age. It was confirmed that the stipe length is the most suitable standard factor for analyzing the structure of the Eisenia population considering the relation between stipe length and the other parts of the frond, and because of the ease it affords in measuring under water.

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