High tolerance of phytoplankton for extremely high ammonium concentrations in the eutrophic coastal water of Dokai Bay (Japan)

概要

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The tolerance of phytoplankton in Dokai Bay for an extremely high ammonium concentrationin culture media has been studied. Six species of phytoplankton, three diatoms (twoclones of Skeletonema sp. and Chaetoceros sp.) and three flagellates (Heterosigma akashiwo,Chattonella antiqua and Karenia mikimotoi) were grown in various concentrations of NH4Cl.The results suggested that high ammonium concentrations had negative effects onphytoplankton growth. Non-indigenous species in Dokai Bay, Japan, C. antiqua and K.mikimotoi, were unable to grow at 200 and 150 μ M, respectively. Growth rates of Skeletonemasp. isolated from Harima Nada (Seto Inland Sea, Japan), Chaetoceros sp. and H. akashiwo werereduced significantly at higher ammonium concentrations compared to the control treatment.However, such a high ammonium concentration of even 1,500 μ M could not produce a significantadverse effect on the growth rate of Skeletonema sp. isolated from Dokai Bay. Furthermore,the maximum chlorophyll fluorescence of tested species was also gradually decreasedwith an increase in ammonium concentration. The influence of a high ammonium level onphytoplankton growth observed in this study confirmed the phytoplankton species compositionobserved in Dokai Bay. Our results suggested that such a high ammonium concentrationwas an important factor in determining the species composition of the phytoplankton assemblage in that bay.
日仏海洋学会の論文
2009-11-28