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[A-5.2 Evaluation of Effects of Increased Ultraviolet Radiation on Marine Phytoplankton Community]

[Contact Person]

Satoru Taguchi
Chief, Biological Oceanography Laboratory
Fisheries Oceanography, Hokkaido National
Fisheries Research Institute, Fishery Agency
116 Katsura-koi, Kushiro 085 Japan
Phone +81-154-91-9136, Fax +81-154-91-9355
Omnet jfa.hokkaido

[Total Budget for FY1990-1992]

29,218,000 Yen

[Abstract]

　Computer controlled incubator with ultraviolet radiation and visible light was constructed for a laboratory experiment. Incubation experiments under UV-B radiation were conducted with green algae Tetraselmis sp. at 32℃, 23℃, and 13℃ which corresponded to the maximum, medium, and minimum growth temperature of this species. Loss of chlorophyll a due to UV-B radiation was the largest at 13℃. While Tetraselmis sp. lost chlorophyll a and b under UV-B radiation, the cells might reduce the UV-B effect by producing carotenoid pigments in their cells. Incubation experiments under the natural solar radiation were conducted with the natural assemblages of phytoplankton in the eutrophic Akkeshi Bay. Enhancement in the photo-synthetic activity and biochemical synthesis was observed in the absence of UV-B. Recovery of the enhancement was not always observed in the photosynthetic activity but in the biochemical properties within 24 hr period.
　Spectral distribution was determined with underwater UV spectrometer and visible light spectrometer in open and coastal water. Estimation of extinction coefficient of downwelling UV was established from the extinction coefficient of blue light. The extinction coefficient of UV was related with decrease of UV wavelength and increase of chlorophyll a concentration. One percentage of the surface UV-B at 305nm and 320nm was found at 12.2m and 16.0m in the open water while at only 1m in the coastal water. The UV-B effective layer occupied 23-30% in the open water and 16-19% of the euphotic layer in the coastal water. This might suggest that the natural assemblages of phytoplankton in the open water seemed to be more receptive than one in the coastal water.
　Comparison of the species composition of natural assemblages of phytoplankton in the coastal water with one previously published might suggest little change for a period of 20 years. This comparison might suggest that phytoplankton cells may go through a damage-recovery phase by a combination of vertical mixing of water and day-night cycle.

[Key Words]

UV-B, Phytoplankton, Chlorophyll a, Tetraselmis sp., Extinction Coefficient