Eutrophication and Occurrences of Harmful Algal Blooms in the Seto Inland Sea, Japan
Plankton Benthos Res 1(2): 71–84, 2006 Plankton & Benthos Research © The Plankton Society of Japan and The Japanese Association of Benthology Eutrophication and occurrences of harmful algal blooms in the Seto Inland Sea, Japan ICHIRO IMAI1*, MINEO YAMAGUCHI2 & YUTAKA HORI3 1 Laboratory of Conservation of Coastal Ecosystems, Graduate School of Global Environmental Studies (concurrent with Laboratory of Marine Environmental Microbiology, Division of Applied Biosciences, Graduate School of Agriculture) Kyoto University, Kyoto 606–8502, Japan 2 Red Tide Research Division, National Research Institute of Fisheries and Environments of Inland Sea, Maruishi, Hatsukaichi, Hiroshima 739–0452, Japan 3 Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Futami, Akashi, Hyogo 674–0093, Japan Received 28 February 2006; Accepted 10 April 2006 Abstract: The Seto Inland Sea is the largest enclosed coastal sea in Japan and is also a major fishing ground includ- ing aquacultures of fish, bivalves and seaweeds. The incidents of red tides dramatically increased in frequency and scale in the Seto Inland Sea along with serious eutrophication in the 1960s and 1970s. The maximum incident of 299 was recorded in 1976, but the incident has since shown a clear decreasing trend, reaching about 100 per year in the late 1980s by virtue of regulation by law, and this level has been maintained thereafter with the level of nutrients supporting red tide occurrences. The “Law Concerning Special Measures for Conservation of the Environment of the Seto Inland Sea” was legislated in 1973 and industrial loading was decreased to half the level of 1972. The important red tide or- ganisms causing huge fishery damages by fish-kill are Chattonella antiqua, C.
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