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Uchiumi Bay experiences intermittent physical events of 'Kyucho ' and bottom intrusion.A Kyucho is an intrusion of warm surface water from the Kuroshio in the Pacific Ocean. Bottom intrusion, which contains a large amount of nitrates, phosphates, and silicates, slips through just above the continental shelf. We investigated seasonal changes in the abundance of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton while monitoring Kyucho and bottom intrusion from March to October 2002. Kyucho and bottom intrusion frequently occurred from June to September. Relatively high concentrations of nitrate + nitrite (> 0.8 µmol N l -1 ) and phosphate (> 0.1 µmol P l -1 ) were found when bottom intrusion occurred. The cell densities of Prochlorococcus were relatively high (>1 × 10 4 cells ml -1 ) when Kyucho occurred. Those of Synechococcus were high (2 to 30 × 10 4 cells ml -1 ) during the period of thermal stratification except in July, when bottom intrusion occurred. The cell densities of eukaryotic picophytoplankton were high (2 to 8 × 10 4 cells ml -1 ) in May and July. To examine the effects on picophytoplankton growth of the nutrients supplied by bottom intrusion, we conducted nutrient-enrichment experiments. The growth rates of Prochlorococcus and Synechococcus were not stimulated by the addition of any kinds of nutrients. The growth rates of Prochlorococcus were negative in most cases. In July, the growth rate of eukaryotic picophytoplankton was stimulated by nitrate and phosphate additions. Thus, Prochlorococcus detected in Uchiumi Bay might have been transported by Kyucho from the Pacific Ocean and could therefore not grow vigorously. Synechococcus may have been flushed out by bottom intrusion, and its growth was not limited by the nutrient concentrations. Eukaryotic picophytoplankton was abundant in spring, and its growth might have been limited by the nutrient concentrations in some cases. These results suggest that Kyucho and bottom intrusion have different effects on the abundance and growth rate of the 3 picophytoplankton groups.

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Gelatinous zooplankton collected and quantified daily at the sluice gate of the Ikata Nuclear Power Station along the coast of Iyo-Nada in the Seto Inland Sea were analyzed for the period 1998-2004 in an effort to correlate the number of these animals with the physical oceanographic conditions. Sudden periodic and nonperiodic increases of gelatinous zooplankton occur repeatedly from early summer to late autumn in nearshore areas. Periodic increases are synchronous with the spring tidal period. Nearshore tide-induced eddy development may play an important role for the aggregation process of gelatinous zooplankton, and the spring-neap tidal variation of the circulation induces increases of the gelatinous zooplankton population in coastal waters of the Iyo-Nada. Nonperiodic increases are attributable to typhoons and other storms. The strong shoreward currents due to the winds caused by these events transport gelatinous zooplankton to nearshore areas.

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