Red tide outbreak of the noxious flagellate Karenia mikimotoi (Dinophyceae) in Hiketa Bay [Japan] in the Seto Inland Sea; Comparison of environmental conditions between a red tide occurrence year and a non-occurrence year
2007
Ichimi, K.(Kagawa Univ., Miki (Japan). Faculty of Agriculture) | Miyao, K. | Montani, S.
Continuous field observations were carried out at a station in Hiketa Bay, in the Seto Inland Sea, in summer, 1996 and 1997, to investigate the relationship between red tide occurrence of Karenia mikimotoi and ambient environmental conditions. In this study, physicochemical parameters and abundances of K. mikimotoi and diatoms in 1996 (red tide occurrence) and in 1997 (non-occurrence) were compared. In 1996, the cell density of K. mikimotoi in July was 10E0-10E2 cells mlsup(-1), after then, thereafter increasing gradually and reaching 18000 cells ml sup(-1) at 0 m on 17 sup(th) August. The cell density of K. mikimotoi in July in 1997 was similar to that in 1996, however, it did not increase further. Apparent differences in the environmental conditions between 1996 and 1997 were concentrations of nutrients and diatom abundance. Phosphate and silicate concentration in 1997 were higher than those in 1996. On the contrary, the concentration of dissolved inorganic nitrogen was higher in 1996 except during the bloom of K. mikimotoi. The cell density of Chaetoceros spp. in 1996 was low ( 10E2 cells ml sup(-1)) through on the survey period. In contrast, the cell density of Chaetoceros spp. in 1997 was 10E2-l0E3 cells ml sup(-1), showing 10 times higher abundance than in 1996. These observations suggest that K. mikimotoi could not grow largely because of higher abundances of diatoms in 1997.
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