The young sporophyte of Ecklonia kurome Okamura is growing on the population floor. This study was designed to estimate the daily light compensation point of the young E. kurome with a mathematical model based on photosynthesis-irradiance relationships, diurnal changes in solar radiation and relative irradiance at the sea floor in the habitat around the Umashima Island, Yamaguchi Prefecture. The samples were collected at a depth of 5m at the habitat. Photosynthesis-irradiance relationships of the young E. kurome using a productmeter were fitted by a hyperbolic tangent function. Maximum gross photosynthesis, respiration, light saturation and light compensation point were 30.0 LO₂ cm^-2 h^-1, 1.88 LO₂ cm^-2 hr^-1, 67.0 mol m^-2 s^-1 and 4.20 mol m^-2 s^-1, respectively. The daily light compensation point of the young E. kurome estimated by the mathematical model was 0.73% of the irradiance on the sea surface for a day of average solar radiation during study period. This estimated value agreed with the light condition actually measured at the growing site of young E. kurome on the population floor, which was 0.74% of the irradiance on the sea surface. The present study was able to clarify the daily light compensation point of young E. kurome from the results of the mathematical model considered with the both of photosynthetic property and the measurement in the field.

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Microsatellite loci in Saccharina japonica (Areschoug) C. E. Lane, C. Mayes, Druehl & G. W. Saunders were searched by the dual-suppression PCR method with several modifications. Within 28 SSRs for which both adjacent regions were able to read, the sequence including the complete primer array was confirmed in only three regions. Therefore, it is suggested that the determination of sequences adjacent to both ends of the SSR region become a key for marker development in this method. Accordingly, in this study, from 2 to 9 alleles were found between individuals in 7 loci and they could be detected by electrophoresis that used acrylamide gel.

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To describe the predominant bacteria attached to the red alga Gracilariopsis chorda (Holmes) Ohmi collected from the estuary of Katsuura River in Tokushima Prefecture in southwest Japan, the bacterial populations and the floras of the naturally occurring algae, the cultured algae, and those found in the environmental seawater were investigated. The viable counts of the heterotrophic bacteria attached to the naturally occurring algae collected in March and June were 6.5×10⁶ and 1.3×10⁶ cells g^-1, respectively. The viable counts of the heterotrophic bacteria attached to the cultured algae in March and June were 5.4×10⁷ and 3.4×10⁷ cells g^-1, respectively. The viable bacterial count in the environmental seawater was 1.2×10⁵ cells ml^-1. Moraxella sp. was predominant in the environmental seawater. The predominant bacteria attached to the naturally occurring G. chorda collected in March and June were Vibrio sp. and Moraxella sp., respectively. After the continuous culture of algae in a sterile medium, Flavobacterium - Cytophaga sp. was predominant and the percentage of Vibrio sp. decreased. These bacterial flora changes suggest that Flavobacterium - Cytophaga sp. is predominant on the red alga G. chorda.

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Community and morphological characteristics of Zostera marina were surveyed at 6 survey stations along the Ehime Prefectural coast in the season of luxuriant growth. The stations were located in different sea areas with different climatological and oceanographical conditions, that is, St. 1 (Ohmi-shima Is.), St. 2 (Asanami) and St.3 (Gogo-jima Is.) in Aki-nada (central Seto Inland Sea), St. 4 (Mitsukue) in Iyo-nada (western Seto Inland Sea), and St.5 (Yoshida), St.6 (Miura) in the Uwa Sea. 　The characteristics were quite different among the stations and among the different depths in each station, and mean shoot densities and biomass ranged 68- 869 shoots m^-2 and 69. 7-171. 8 gDW m^-2 respectively among the stations. In general, Z. marina communities were constituted by larger shoots in size with lower densities in the stations of Aki-nada, and by smaller shoots with higher densities in the stations of Iyo-nada and the Uwa Sea. Especially, shoot density in St. 6 was quite higher which is 869 shoots m^-2 in mean (and 1,185 shoots m^-2 in the densest place). The below-ground parts of the Z. marina communities in Iyo-nada and the Uwa Sea were more developed than those in Aki-nada, which was shown in their ratio of below-ground biomass to total biomass. The variation in morphological and community characteristics observed here was considered to reflect the phenotypic plasticity of Z. marina expressed under various physical conditions of the habitats, as well as genetic variations among local populations.

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