Goro Yoshida

Ecology and restoration techniques for Sargassum beds in the Seto Inland Sea, Japan

Due to the reduction and degradation of coastal areas in Japan by land reclamation and anthropogenic perturbations, from the point of view of conservation of the coastal environment, the restoration of Sargassum beds is essential. Between 1978 and 1991, 6400 ha of seagrass and seaweed beds have been lost along the Japanese coast, of which Sargassum beds were 22%. New techniques for Sargassum bed restoration are summarized based on three coastal engineering techniques. (1) Construction of shallow and gentle sloping bottom substrata have been shown to be effective for the reestablishment of management-free seagrass and Sargassum beds on developed coasts. (2) Seeding or transplanting using artificial substratum for extension of nursery and fishing grounds around natural Sargassum beds. (3) Periodic transplanting of Sargassum plants using artificially produced seedlings is effective to produce niches to allow faunal re-colonization in severely polluted and sparsely vegetated area. However, prior to implementation, the suitability and limitations of these three techniques requires to be ascertained for effective Sargassum bed restoration.

Growth and maturation of the ‘autumn-fruiting type’ of Sargassum horneri (Fucales, Phaeophyta) and comparisons with the ‘spring-fruiting type’

The growth and maturation period of the autumn‐fruiting population ot Sargassum horneri C. Agardh (Phaeophyta) was investigated in Hiroshima Bay, Seto Inland Sea. Surveyed traits were compared to those of the spring‐fruiting type and ecological features of this species were discussed. The annual lifetime of the autumn‐fruiting population could be divided into four phases according to the daily increase in thalius length:phase I from December to May (increase in length < 0.1 mm/ day), phase II from May to September (= 0.3–1.0 mm/ day), phase Ml (from September to December > 10 mm/day) and phase IV which was the senescence phase from December to March. Receptacle formation‘as observed in November and gamete release from November to February. Conversely, the spring‐fruiting type germinated in April and exhibited swifter growth in its early stage of development than the autumn‐fruiting type. Rapid increase in thalius iength in autumn was common in both fruiting types, although the spring‐fruiting type continued to grow during winter. Receptacle formation of the spring‐fruiting type started in February but gamete release was not observed until April and May. The difference in life‐history patterns of both types of S. horneri was in the overwintering period. The autumn‐fruiting type spent that season as germi‐ings or as young plants exhibiting slow‐paced growth, while the spring‐fruiting type overvwintered as adult thal‐li preparing for gamete release in spring.

Porphyra migitae sp. nov. (Bangiales, Rhodophyta) from Japan

Kikuchi N., Arai S., Yoshida G., Shin J.-A., Broom J.E., Nelson W.A. and Miyata M. 2010. Porphyra migitae sp. nov. (Bangiales, Rhodophyta) from Japan. Phycologia 49: 345–354. DOI: 10.2216/09-82.1 A new species of Porphyra, Porphyra migitae sp. nov., coloured fire red and collected subtidally in two localities in Japan, is described based on morphology, life history and molecular analyses. The new species can be distinguished from other fire-red coloured Porphyra species by a range of characters including the presence of conchospores and many archeospores and neutral spores on foliose thalli. Foliose thalli, which are sometimes lobed, are monoecious, and clearly distinguishable patches of spermatangial sori are not formed. Many holes are formed on the foliose thalli after release of spermatia. This species has a heteromorphic life history in which the macroscopic gametophytic foliose thalli alternate with the microscopic sporophytic filamentous thalli (conchocelis). In addition, the life history includes additional reproductive cycles of the foliose thalli via archeospores and neutral spores. This species has the widest range of asexual reproductive strategies so far observed in the Bangiales. Molecular phylogenies based on both the nuclear SSU rDNA and the rbcL genes enable this species to be distinguished from other species of Porphyra for which there are equivalent data.

Ecotypic differentiation in maturation seasonality among Sargassum horneri (Fucales, Phaeophyta) populations in Hiroshima Bay, Seto Inland Sea, Japan

Abstract Seasonal changes in plant length and maturation rate were surveyed for eight populations of Sargassum horneri in and around the Hiroshima Bay area, Seto Inland Sea, Japan. Six populations were chosen from the innermost to the exterior part of Hiroshima Bay, and two populations from the inner and outer parts of Yanai Bay, which is adjacent to Hiroshima Bay. A seasonal gradient in the peak of plant length and maturation was observed among populations from the inner to the outer parts of the two bays. Populations inhabiting the inner area of the bays reached the maximum plant length and peak in maturation in autumn, and decayed in winter. Only germlings were found at the habitats in the inner area of the bays in spring. On the contrary, populations inhabiting the mouth and outer area of the bays contained no mature plants in autumn, but plants gradually began producing receptacles during winter and reached the peak in maturation in spring. Seedlings from two inner-bay and two outer-bay populations were transplanted to the inner part of Hiroshima Bay in order to compare their seasonal growth and maturation. Although summer growth of seedlings was inhibited due to the effect of sedimentation, each seedling exhibited the original maturation seasonality of the population of its original habitat. We concluded that differences in seasonality among the S. horneri populations are attributable to a genotypic difference, rather than to phenotypic plasticity.

Development of adventive embryos in cauline leaves of Sargassum macrocarpum (Fucales, Phaeophyta)

Spontaneous formation and development of adventive embryos were observed in cauline leaves of Sargassum macrocarpum in laboratory culture. Semi‐spherical swellings, which were 200–250 μm in diameter, arose from the surface of cauline leaves of thalli cultured for 4 months from zygotic embryos. Swellings became cylindrical protuberances and grew into ‘daughter’ thalli with one or two small cauline leaves. These thalli detached from ‘mother’ thalli and attached to the surface of culture vessels by rhizoids produced within 1 week after detachment. Each daughter thallus developed into an individual thallus exhibiting the same morphological processes as zygotic embryos.

Variation in biomass and species composition of epiphytic community on the different aged leaves of Zostera marina (Chlorophyta)

The development of the epiphytic community on the leaves of Zostera marina was followed by comparing variations in epiphytic organic carbon, chlorophyll a, cell abundance, and species composition between the younger and older leaves. Biomass of epiphytic community on Z. marina depended on leaf age; particulate organic carbon and cell abundance on the older leaves were 21 and 192 times higher than those on the youngest leaves, respectively. The abundant taxa of epiphytic community were Leptolyngbia sp. (Cyanobacteria), Cocconeis scutellum, Campylopyxis garkeana, and Gomphonemataceae (Bacillariophyceae), and the change of species composition of epiphytic community was independent on the leaf age. Significant relation between CHLa and POC showed organic matter on the leaves was consisted of algal cells. The amount of epiphytic POC was well correlated with diatom cell abundance (P<0.1), but not with total cell abundance. The prevalence of diatoms instead of Cyanobacteria on the leaves was shown by both chemical and taxonomic analyses. Low POC/DW ratios of epiphytic community on the older leaves indicated that inorganic suspended particles were more likely to adhere.