Problems in the identification of "Sargassum duplicatum" group

The morphological variations of characteristics of leaves and vesicles were studied in a Sargassum duplication Bory population from Owase, Mie Prefecture, Japan. Even in this small population, four morphologically different plants (type 1, 2, 3 and 4) were distinguished by their characteristics of leave and vesicles, as follows. Type 1 had slender oblanceolate leaves and entire vesicles, type 2 had broader elliptical leaves and apiculated, or crowned or phyllocyst vesicles, type 3 had slender lanceolate leaves and variable vesicles, and type 4 had broader elliptical leaves and entire or apiculated vesicles, respectively. However, these all plants from Owase showed scutellate holdfasts and slightly compressed primary branches. From the characteristics of holdfast, primary branch and dioecious sexuality, all these plants (type 1 to 4) from Owase should be identified as Sargassum duplicatum Bory having very wide variation ranges of leaves and vesicles, regardless of few cup-shaped characteristic leaves. Typical S. duplicatum has been usually distinguished its morphology of cup-shaped leaves, vesicles with horn-like appendages and dioecious sexuality in the receptacles. On the other hand, typical S. crassifolium showed the leaves with double seriated margin, phyllocyst-like vesicles, and monoecious sexuality in the receptacles. However, there were some confusing on the morphology of these leaves and vesicles, so these two species were now called the member of "S. duplicatum" group including several species (S. cristaefolium, S. turbinatifolium, S, turbinarioides et al.). From the wide variation in the leaves and vesicles of S. duplicatum in Japan as above, we need furthermore study of morphological variations and DNA analysis on these species in the East Asian and Southeast Asian populations

THREE SPECIES OF SARGASSUM (PHAEOPHYCEAE) WITH COMPRESSED PRIMARY BRANCHES IN THE GULF OF THAILAND

Three species of Sargassum with compressed primary branches, S. binderi Sonder, S. oligocystum Montagne and S. swartzii (Turner) C.A. Agardh, have been described from the Gulf of Thailand. S. swartzii is the first record of this species from the coast of Thailand. A key for these three species and for each species descriptions have been completed. The clear distinction among these three species is clearly shown and discussed. S. binderi has slender lanceolate leaves, a dentate margin along the compressed stem of its vesicles, and clear spines along the whole margin of the flattened receptacles. S. oligocystum has broader lanceolate leaves with an acute to rounded apex, almost entire, spherical vesicles, and only few spines on the margin of the slightly compressed receptacles. S. swartzii has linear lanceolate leaves, pointed or crowned vesicles, and few spines neat the tip of its almost terete receptacles

Seasonal distribution of Gambierdiscus spp. in Wakasa Bay, the Sea of Japan, and antagonistic relationships with epiphytic pennate diatoms

The occurrence of the ciguatera fish poisoning (CFP) causative Gambierdiscus spp. was confirmed in the Sea of Japan for the first time in 2009. This paper reports seasonal distribution of Gambierdiscus spp. and epiphytic diatoms in the Sea of Japan. Monitoring results suggested an antagonistic interaction in abundances between epiphytic diatoms and the dinoflagellate Gambierdiscus spp. Allelopathic effects of diatoms were considered to be involved in the competitive phenomenon. Therefore it is hypothesized that cell densities of epiphytic pennate diatoms on macroalgae are a novel determinant affecting the abundance of Gambierdiscus spp. other than sea water temperature, salinity and nutrients. Monitorings of the abundance of epiphytic diatoms would lead us to predict the occurrences of Gambierdiscus spp. blooms in the CFP area, and thereby the CFP risk assessments would be developed. Phylogenetic analyses indicated that Gambierdiscus spp. in the Sea of Japan belonged to Gambierdiscus sp. type 2 which was reported to be non-toxic. Nevertheless, based on morphological characteristics, at least two types of Gambierdiscus spp. were found in the Sea of Japan. It is needed to test the toxicity of the both types of Gambierdiscus recognized in the present study for evaluation of the probability of CFP outbreak risks in the Sea of Japan in the future