Masao Ohno

Crossing test among floating Ulva thalli forming ‘green tide’ in Japan

Crossing tests were made to determine the relationship between the identified Ulva pertusa, which commonly grows in Japan as an attached form on exposed rocks, and the floating Ulva forming green tide inside calm bays. The floating Ulva thalli were collected from five major green tide sites in Japan (Yokohama, Mikawa, Miyajima, Kochi and Hakata). Reproductive maturation was induced in U. pertusa and the floating thalli from each site. Mating between induced gametes was observed. It is therefore believed that the floating thalli from Yokohama, Mikawa and Miyajima were mainly U. pertusa, while those from Kochi and Hakata were of a different species (Ulva sp.1). Furthermore, the Ulva species found in Mikawa is also a species (Ulva sp.2) different from both U. pertusa and Ulva sp.1.

Seaweed micropropagation techniques and their potentials: an overview

The seaweed industry worldwide uses 7.5–8.0 million tonnes of wet seaweeds annually with a majority of it derived from cultivated farms, as the demand for seaweed based-products exceeds the supply of seaweed raw material from natural stocks. The main advantage of cultivation is that it not only obviates overexploitation of natural populations but also facilitates the selection of germplasm with desired traits. To enhance the economic prospects of seaweed cultivation, varied practices, such as simple and cost effective cultivation methods, use of select germplasm as seed stock coupled with good farm management practices, etc., are adopted. Nevertheless, in vitro cell culture techniques have also been employed as they facilitate development and propagation of genotypes of commercial importance. There are more than 85 species of seaweeds for which tissue culture aspects have been reported. Although the initial aim of these techniques focuses mostly on genetic improvement and clonal propagation of seaweeds for mariculture, recently the scope of these techniques has been extended for use in bioprocess technology for production of high value chemicals of immense importance in the pharmaceutical and nutraceutical sectors. Recently, there has been a phenomenal interest in intensifying seaweed tissue and cell culture research to maximize the add-on value of seaweed resources. This paper deals with the status of seaweed micropropagation techniques and their applications in the context of the marine biotech industry. Further, it also provides an analysis of the problems to be resolved for removing the barriers that are impeding the true realization of potentials offered by these techniques for sustainable development and utilization of seaweed resources.

Seasonal variation in the physical properties of agar and biomass of Gracilaria sp. (chorda type) from Tosa Bay, southern Japan

Plants of Gracilaria sp.(chorda type), which grow along the coast of Uranouchi Inlet in Tosa Bay, southern Japan, showed the highest biomass in the summer (26 °C to 31 °C) and spring season (15.1 °C to 24.9 °C). Maximum biomass was 6952 g m−2 in July, but gradually decreased in the autumn (30.5 °C in September to 20 °C in November) and winter (19.5 °C in December to 14.9 °C in February). Variation in yields and gel strength of the agars, were shown to depend on the time in the season. After alkali treatment (5% NaOH, 2 h) at three different temperatures (70, 80, and 90 °C), the agars showed gel strengths essentially that of commercial grade agars, with the best gel obtained at 80 °C. Maximum gel strength (1455 g cm−2 of 1.5% agar gel) occurred in winter when the biomass and agar yield were low. Minimum gel strength was in spring. Gel strength was inversely correlated with agar yield, but was positively correlated with apparent viscosity. Maximum viscosity was 40 cP. in December. Gelling temperatures, pH of 1.5% agar gel, and moisture content in agars showed little variation.

Seaweed succession on artificial reefs on different bottom substrata

Artificial rest reefs were set on sandy and rocky bottoms at 5–10 m depth along the coast of southern Japan. Mature thalli ofSargassum, Gelidium and other seaweds were transported from other coastal areas, packed in mesh bags and attached to the reefs to start the beds. After one year, the seaweed flora on the reef on a sandy bottom consisted of more than 20 species, includingSargassum spp. andGelidium amansii, which are important animal food species. Coralline algae were the dominants on the rocky bottom reefs. The lower biomass on reefs on the rocky bottom was due to grazing by urchins. The same number of species was present in the first and second years on reefs on sandy bottoms, but there were moreSargassum thalli the second year.Maximum algal biomass of the artificial reef in May of the second year was 9998 g wet wt m−2 in sandy areas, 441 g wet wt m−2 in boulder areas and 228 g wet wt m−2 in rocky areas. Reefs on rocky bottoms continued to be covered by coralline algae and several species ofCodium andDictyota.

3,6 anhydrogalactose, sulfate and methoxyl contents of commercial agarophytes from different geographical origins

The chemical composition of agars extracted from six economically important species of Gracilaria from different geographical sources (Argentina, Brazil, Indonesia, China and Turkey) and one species of Gracilariopsis (G. lemaneiformis) collected from two different Japanese localities was investigated. Agar was extracted by pretreatment with various concentrations of NaOH (3%, 5%, 7%, 10%) for 2 h at 80°C. The sulfate, 3,6-anhyd, rogalactose and methoxyl contents of each agar extract were analyzed. High sulfate and 3,6 anhydrogalactose contents were found in non-alkali treated agar from Turkish Gracilaria gracilis (3.4%) and from Chilean G. chilensis (54.3%) after alkali treatment concentration of 5% NaOH, respectively. High methoxyl contents (4.9%) were obtained from non-alkali treated agar from Chinese G. tenuistipitata.

Observation on the floating seaweeds of near-shore waters of southern Japan

An abundance of floating seaweeds appears with ocean currents around Japan. Young fishes, especially juvenile yellowtail, Seriola quinqueradiata Temminck & Schlegel (2–15 cm in fork length), which live together with floating seaweeds during spring to early summer, are collected and cultured on a large scale by fishermen. To protect the yellowtail resources, many fisheries scientists have been conducting surveys of the distribution and quantity of floating seaweeds every year. It has become important to know the character of floating seaweeds in both quantity as well as quality for fisheries resources