No abstract

Distributions of seaweed/seagrass communities were determined from 230 sites along the coast of Kagoshima Bay, southern Japan, during a series of surveys in 2006. Sargassum (brown algae) and Zostera (angiosperm) communities were conˆrmed from 159 and 41 sites, respectively. Of the 19 species of Sargassum and Zostera conrmed in this study, distributional characteristics of 12 major species were also elucidated. Kagoshima Bay is comprised of three diŠerent areas (back, central part and mouth of the bay) as deˆned by the in‰uence of waters entering the bay from the Kuroshio Current. Two Zostera species, Z. marina and Z. japonica, and four temperate species of Sargassum, S. fusiforme, S. hemiphyllum, S. patens, and S. piluliferum, were conˆrmed from all areas.Meanwhile, six subtropical and warm-temperate species, S. alternato-pinnatum, S. crispifolium, S. cristaefolium, S. duplicatum, S. glaucescens, and S. incanum, were not detected in Kagoshima Bay except for some sites, as indicated by a previous survey in 1976; however, we detected them from various sites in the central part and mouth of the bay. We suggest that these species appeared and developed communities in the past 30 years.

Although sediment deposition has detrimental effects on macroalgal settlement and recruitment, fucoid algae (mainly Sargassum duplicatum) thrive on rocky reefs always overlaid with fine sediments in sheltered sites of Kagoshima, Japan. The aim of the present study was to assess their ability to settle and recruit onto sedimentcovered substrata. A transplant experiment using boulders with Sargassum juveniles attached showed that the 30-day survival rate was as high as 50% even for the juvenile stage (\10 mm) on boulders completely buried with sediment. In addition, an outdoor tank experiment testing the effects of different sediment thicknesses (0-4 mm) on already settled 4-day old S. duplicatum germlings indicated significant reductions in growth by the presence of sediment cover even at 0.5 mm but no significant increase in mortality up to 2 mm. Furthermore, an in situ experiment in which sterilized cobbles were placed at a sediment-covered site to allow sediment to settle over them before the embryo release showed a uniformly high recruitment of Sargassum over the cobbles. This suggests the presence of unknown mechanisms to allow the settlement of propagules on substrata thinly but completely covered by fine sediments.

The Zostera marina bed is an important habitat for the biological productivity and diversity of coastal marine organisms including various importantˆshery species. Seed dispersal is a deˆnitive factor to that regulates the annual Z. marina production and is inportant for maintaining the annual Z. marina beds. This study examined the seed dispersal dynamics of the annual Z. marina based on a molecular analysis using 7 microsatellite markers and measuring the morphological characteristics of thallus in Kagoshima Bay, Japan. Samples for DNA analysis and morphological measurement were collected fromˆve local populations at 10 sites where annual Z. marina was found to be growing. Morphological characteristics of the Z. marina samples diŠered among local populations with diŠerent environmental conditions. Moreover, pairwise Fst values of microsatellite locus calculated from thê ve populations ranged from 0.112 to 0.415 (mean＝0.273), suggesting that the genetic diŠerentiation among local populations was markedly large. The results of this study indicated that the seed dispersal of annual Z. marina among local populations has rarely occurred for a long time.