Marine algae from the Cape of Iwai on the Pacific coast of northeastern Honshu, Japan

Monthly collection of marine algae and sea grasses was carried out from the intertidal and subtidal zones at the Cape of Iwai on the Pacific coast of northeastern Honshu, Japan (38:49N, 141:36E) from February through December 2002. A total of 108 species of marine algae, 14 of which belong to Chlorophyta, 24 to Phaeophyta and 70 to Rhodophyta, and two species of sea grass were identified. Those appearance and maturation periods were shown in Fig. 1. Taniguchi (1) classified the marine algae and sea grasses into the five life form groups, crustaceous algae, small annual algae, small perenuial algae, large annual algae and large perenuial algae. Process of the successions in subtidal zone was described as altering dominant life form groups of the four phases : pioneer, small anuuals and crustaceous algae ; early sere, crustaceous algae ; late sere, small perennials ; climax, large perennials. The season of nudation on reefs have an effect on a speed of the process associated with maturation periods of each life form group (1). The marine algae and sea grass collected from the Cape of Iwai were classified into those life form groups, and the maturation periods were observed. Sixty four small anuuals as pioneer phase occurred, in which 17-20 species matured in spring. Among 32 species of small perennials as late seral phase, the maturation periods were mainly divided into the three seasons, spring such as Analipus japonicus and Gloiopeltis furcata, autumn such as Dictyota dichotoma, Dilophus okamurae, and Calpopeltis affinis, and year-round such as Gelidium and Gracilaria Among large perennials as climax, the five fucoids species of Hizikia fusiforme, Sarqassum micracanthum, S. confusum, S. thunbergii, and S. yessoense matured in summer, and the kelp Eisenia bicyclis did in autumn. No reproductive cells of 3 species of crustaceous algae was observed. Among 4 species of large perennials occurred, only sporophylls of Undaria pinnatifida was observed from spring to summer. The floral index of I/H have been used to evaluate whether marine algal flora affect warm or cold current system (2). There, 'I' indicates the number of species with isomorphic altenation of generations and lacking gametophytic generation in both Chlorophyta and Phaeophyta. 'H' indicates the number of species with heteromorphic altenation of generations. Along the Pacific coast of northen Tohoku from Oshika Peninsula, where are located in subarctic floral zone (3), I/H values were 1.22 in Shimokita Peninsula (4), 1.35 in Miyako (5), 1.41 in Kitakami (6), 1.9 in Ogatsu (7) and 1.18 in Tomarihama. The value in the Cape of Iwai was 1.38, belonging to subarctic floral zone typically.