Abstract
Temporal variation in the wintertime diatom community structure in Tokyo Bay was investigated from 1981 to 2000 with respect to possible environmental influences. A previous study found that rapid industrialization around the 1960s altered the diatom community. We found that a similar eutrophic-type community with low species diversity dominated by Skeletonema costatum sensu lato (s.l.) still prevailed in 2000, despite recent relaxation of eutrophic conditions. When the cell density and carbon biomass of S. costatum s.l. declined from the mid 1980s to the late 1990s, diatom communities dominated by various species occurred sequentially and species diversity increased. Principal components analysis on environmental factors revealed that S. costatum s.l. favored typical wintertime conditions in the Tokyo district, sunny (less rain) and cold. In contrast, cloudy and warm conditions from the mid 1980s to the mid 1990s were responsible for the decline in S. costatum s.l., allowing other diatom species to grow. The second most important species, Eucampia zodiacus, favored windy years, presumably with strong advection and vertical mixing. The interannual variation of S. costatum s.l. and E. zodiacus populations was out of phase, suggesting that these species had responded to different climatic forcing at different temporal scales.
