A meso-scale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in 2004 summer.The iron-patch was traced for 26 days which included observation of development and declineof the bloom using mapping of inert tracer sulfur hexafluoride.The experiment was made at almost the same location and the same season to SEEDS (previous iron-enrichment experiment).However,the results were quite different between SEEDS and SEEDS II.The SEEDS was characterized by high accumulation of phytoplankton biomass accompanied by a floristic shift from oceanic diatom to neritic diatoms.In contrast,in SEEDS-II,surface chlorophyll-a accumulation was lower,0.8 to 2.48 mg m -3,without a prominent diatom bloom.Photosynthesis competence in terms of Fv/Fm for the total phytoplankton community in surface waters increased after iron enrichments and returned to the ambientlevel by day 20.These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron-enrichments and returned to an iron-stressed condition during the declining phase of the bloom.In the declining phase,pico-phytoplankton (<2μm) became dominant in the chlorophyll-a size distribution.We observed a nitrate drawdown of 4.1 μM in the patch (day 21),but silicic acid concentration was not significantly different between inside and outside the patch.Mesozooplankton (copepod) biomass,which was dominated by the ontogenetic vertical migrator Neocalanus plumchrus,was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS.N.plumchrus population was mainly composed of second and third copepodite stages at the beginning of the experiment and of fifth copepodite at the end of the observation.We concluded that the copepod grazing prevented the formation of a massive diatom bloom as is observed in SEEDS andlead to the change in the pico-phytoplankton dominated community toward the end of the experiment.