Phenology of Sargassum duplicatum (Fucales, phaeophyceae) from the southern coast of satsuma peninsula, kagoshima, Japan

The seasonal change in biomass and morphology of Sargassum duplicatum Bory (Fucales, Phaeophyceae) was examined during January 2002 to May 2003 at Bandokorobana Park, Kagoshima, Japan, located on the southern coast of the Satsuma Peninsula. A 100-m line transect at an exposed location revealed that S. duplicatum inhabits the rocky shore of the intertidal zone (0.05 m to 0.6 m upper mean sea level of Japan). The biomass (24.5 +/- 3.025 g wet weight; mean +/- standard error) and thallus length (263.3 +/- 15.377 mm) were greatest during June and the population density was highest in March (1100 individuals/m(2)). After maturing in June, individuals disintegrated and were absent from October until January 2003, when new juveniles increasing in biomass and thallus length were observed. However, numerous wounded and bleached thalli were detected in March 2003 and further increases in biomass, thallus length, and population size ceased. In contrast, S. duplicatum growing in a less exposed location developed as expected. It is likely that the wounds and bleaching were caused by a combination of grazing fish and environmental factors, which led to the failure of the exposed population to establish during 2003.