Eutrophication and occurrences of harmful algal blooms in the Seto Inland Sea, Japan

By I. Imai, M. Yamaguchi, Y. Hori. 2006

276 citations recorded by the source corpus.

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. marina, C. ovata and Heterosigma akashiwo (Raphidophyceae), and Karenia mikimotoi and Cochlodinium polykrikoides (Dinophyceae). The maximum fishery damage (death of 14.2 million yellowtails) was 7.1 billion yen (about US $60 million) caused by C. antiqua in Harima-Nada in 1972. In 1988, a novel red-tide dinoflagellate species Heterocapsa circularisquama appeared for the first time, and has repeatedly killed both natural and aquacultured bivalves, with the highest damage of 3.9 billion yen to cultured oysters in Hiroshima Bay in 1998. Among the important red-tide organisms, C. antiqua, H. circularisquama and C. polykrikoides are rated as extremely harmful species that can easily reach the warning level of fishery damage by consuming only small amounts of nutrients. In toxic blooms, the dinoflagellate Alexandrium tamarense has become dominant in the Seto Inland Sea in the spring season, causing toxicity in short-necked clams and cultured oysters al- most every year. Many countermeasures have been applied for harmful algal blooms in Japan. Laws for the regulation of water quality have been most effective in decreasing red-tide occurrences. No physical and chemical controls have been successful except for clay treatments. Clay spraying has been investigated and implemented in Kyushu and Korea for the removal of C. polykrikoides red tides. As environment-friendly mitigation strategies for red tides, biological con- trols using algicidal bacteria and viruses are proposed. A new finding of the abundant existence of algicidal bacteria on the surface of seaweeds suggests that co-culturing fish and seaweed is a prevention strategy for harmful algal blooms by virtue of the continuous release of many algicidal bacteria to the surrounding seawater. The artificial development of seaweed beds would also be effective as a prevention strategy for red tides.

Subfields: Environmental Chemistry, Oceanography

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In Environmental Chemistry

1. P. Glibert
2. J. Burkholder
3. C. Gobler
4. W. Cochlan
5. D. Anderson
6. T. Smayda
7. C. Heil
8. H. Yokoyama

In Oceanography

1. P. Glibert
2. J. Burkholder
3. C. Gobler
4. T. Smayda
5. W. Cochlan
6. D. Anderson
7. C. Heil
8. D. Stoecker

Citations in the corpus

• Life cycle, physiology, ecology and red tide occurrences of the fish-killing raphidophyte Chattonella (2012, unknown): “In order to evaluate the degree of danger and harm of C. antiqua, the warning level of cell density was converted to equivalent level of inorganic nutrients of nitrogen and phosphorus based on minimum cell quota for N (qN0 ) and P (q P 0) (Imai et al., 2006b).”
• Eutrophication and Harmful Algal Blooms: A Scientific Consensus (2008, background): “The number of red tides began to decrease in 1977, eventually falling to less than 30% of the peak frequency, which had been in excess of 300 blooms year"1 (reviewed by Imai et al., 2006).”
• Growth and food source of the sea cucumber Apostichopus japonicus cultured below fish cages — Potential for integrated multi-trophic aquaculture (2013, background): “Such environmental deterioration often produces negative consequences for farm management such as death of fish due to harmful algal blooms (Imai et al., 2006) and fish diseases (Pillay, 2004).”
• Nutrient and Phytoplankton Dynamics in Harima-Nada, Eastern Seto Inland Sea, Japan During a 35-Year Period from 1973 to 2007 (2010, background): “Eutrophication caused the number of red tides to increase exponentially during the 1960s and 1970s, peaking at 299 events per year in 1976 (Imai et al. 2006).”
• Complexity in the eutrophication–harmful algal bloom relationship, with comment on the importance of grazing (2008, background): “, 2001), and raphidophyte and dinoflagellate bloom patterns in the Seto Inland Sea (Imai et al., 2006).”
• Harmful dinoflagellate blooms caused by Cochlodinium sp.: Global expansion and ecological strategies facilitating bloom formation (2012, unknown): “For example, both Imai et al. (2006) and Verity (2010)”