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A-5.3.2 Effects of Enhanced UVB Radiation on Primary Production in the Ocean

[Contact Person]

Satoru Taguchi
Professor
Department of Bioengineering, Faculty of Engineering
Soka University
1-236 Tangi-Cho, Hachiouji, Tokyo 192-8577
Phone: +81-426-91-8002 Fax: +81-426-91-8002
e-mail: staguchi@t.soka.ac.jp

Total Budget for FY1996-FY1998

7,987,000 yen (FY1998: 2,603,000 yen)

Abstract

Underwater penetration of ultraviolet radiation (UVB and UVA) was determined in relation to photosynthetically available radiation (PAR) at St. M in Sagami Bay during the period from June 1995 to December 1998. Relative penetration of UVR to the euphotic layer indicated a strong seasonality with high in winter and low penetration in summer. This seasonality was related with spring increase of chlorophyll a concentration, which was followed by summer increase of dissolved organic matter. Consequently UVB/(UVA+PAR) ratio indicated maximum in summer and minimum in winter. Inhibition rate of primary production was high from May to August, reaching to 41%, and low from January to April. When smaller cells than 10um were dominant and UVB increased in summer, the inhibition rate of primary production increased significantly.
UVB exposure experiments indicated the most vulnerable effect on diatoms, medium effect on prasinophyceae, and least effect on green algae. This result strongly suggests species difference in their tolerance to UVB.

[Key Words]

Penetration, UVB/(UVA+PAR) ratio, Cell size, Inhibition rate, Primary production