Toshinobu Terawaki

Management-free techniques for restoration of Eisenia and Ecklonia beds along the central Pacific coast of Japan

Because of the importance of seaweed resources for conservation of thecoastal environment, the provision of habitats of commercially importantspecies and because of use as human food, a study was carried out on bedsof Eisenia bicyclis and Ecklonia cava. This included the mostimportant environmental factors and the development of techniques forrestoration and long-term maintenance of the beds. At a site chosen fordetailed study, the Eisenia and Ecklonia bed was influenced bymany factors, including desiccation, rainfall, low salinity, low light intensity,turbidity, accumulation of suspended sediments, cover by adhering animals,wave and current action and grazing pressure. The distribution of suchseaweed beds is also limited locally by the size and hardness of rock on thebottom, and by fluctuations in the sand level at the base of the reefs.The management-free technique of creating Eisenia and Ecklonia beds is based on an understanding of the factors limiting the localdistribution of the beds. Conditions for seaweed growth can then beartificially enhanced by coastal engineering. Suggestions to enhance Eisenia and Ecklonia bed restoration using management-freetechniques include raising the bottom, elevating substrata above the sandybottom, and providing substrata of a shape suitable for the attachment ofkelp.

Ecology of seaweed beds on two types of artificial reef

Artificial reefs for the development of valuable fishery resources wereplaced on sandy substrates at 8, 10 and 13 m depths in Muronohana,Ikata, Japan, and observed monthly or bimonthly from February 1999 to June2001.Enteromorpha intestinalis and Colpomeniasinuosa were the primary dominants in spring. The number of seaweedspecies at all the sites gradually increased in winter. Each reef reached aclimax stage of Sargassum spp., Eckloniakurome and Padina arborescens within 18 months.Overall, 38 seaweed species were found during the study.The settlement of kelp, such as E. kurome, was promoted byreduced sand cover as a result of turbulence. Large-scale surface roughnesscould be important in maintaining the communities after initial establishment.

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.

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.

A morphometric comparison of Ecklonia kurome (Laminariales, Phaeophyta) from Japan*

A morphological comparison was made of Ecklonia kurome Okamura collected from seven localities, including a lectotype locality (Shirahama), in Japan. Morphometric characters and their size ranges were recorded as follows: the central lamina width (5.1–67.8 cm), the median fascia thickness (0.9–3.3 mm), the primary pinna width (2.2–24.0 cm), the ratio of width to length of the primary pinna (0.07–0.56) and the primary pinna number index (PPNI; 0.24–2.21). The results suggested that the morphological variations observed within this species were related to their habitat. A thick and distinct median fascia and an undulate central lamina margin were found on plants from moderate wave‐exposed locations. Plants having narrow primary pinnae with indistinct ruga were observed on shores facing open sea. Wide and thin plants grew in wave‐sheltered habitats. Flat plants were found on a shore exposed to a continuous strong current throughout the year. There were noticeable differences in morphology among the Tateyama, Tsuno, Aburatsubo and Tonoshima populations. The yellow and crisp primary pinna edge was a major characteristic of the Tateyama population. Narrow plants in which the central lamina and primary pinnae were half as wide as those of the Shirahama population were found in Tsuno. Wide and thin plants were observed in Aburatsubo. In this locality, the central lamina and primary pinnae were nearly three times wider but half the thickness of those of the Shirahama population. Flat plants grew in Tonoshima. The Muroto and Oki populations exhibited morphologically similar characteristics to the Shirahama population. A hollow stipe and slightly high PPNI value were found in the Muroto population, and a slightly low PPNI value was found on the Oki population.

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.