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    General

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    • Japanese URL

    • In the autumn of 2021, a large-scale harmful red tide that suddenly occurred over a wide area of the Pacific coast of east Hokkaido caused extensive damage to important Hokkaido fishery resources such as salmon and sea urchins, and brought the largest red tide damage in Japan, totaling close to 10 billion yen. The planktonic algae responsible for the outbreak was a dinoflagellate species, Karenia selliformis, which has never been reported to cause red tides in Japan before.

      Several factors have been cited as contributing to the K. selliformis outbreak, including the high water temperatures observed in the area in the summer of 2021, which was referred to as an “ocean heat wave”, and the lack of typhoons in the fall. However, this the large-scale harmful red tides that occurred over a wide area of the open ocean may be caused by different factors than those that have occurred in the coastal and inner bay areas of Japan in the past such as the shallow waters of the Seto Inland Sea and Ariake Sea. In addition, while salmon, sea urchins, whelks, and octopuses were severely affected, such as dying, crab and scallops that inhabited the same waters were less affected, so it is suggesting that the toxic effects of red tides vary by taxonomic group. At present, however, the toxic components of K. selliformis remain unknown.

      In response to the outbreak of red tide in the eastern part of Hokkaido, two major studies are currently underway. The first is the elucidation of the causes of the red tide and the development of prediction methods, and the second is the elucidation of the harmful effects of the red tide on aquatic organisms. In this course, we will summarize the results of research conducted at the School of Fisheries Science, Hokkaido University, and research being conducted at related research institutes such as the Hokkaido Research Organization and the Japan Fisheries Research and Education Agency, as well as introduce general knowledge about red tides and phytoplankton.


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    Individual courses related to the red tides in east Hokkaido in 2021

    • Toxic substances produced by dinoflagellates that cause red tides Distribution of chlorophyll-a and nutrients in the red tide outbreak area off the coast of Akkeshi (October 2021) Phytoplankton observation of red tides in east Hokkaido
    • Analysis of the horizontal distribution of harmful red tides along the Pacific coast of Hokkaido, Japan, in autumn 2021 ComingSoon
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    Red tides and phytoplankton

    • Suppression of red tide and blue-green algae by algaecidal bacteria Spring bloom and surface mixed layer
    • Collection of planktonic organisms by plankton nets ComingSoon
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    What is red tide?

    • A phenomenon in which phytoplankton in seawater proliferate abnormally, causing the sea to appear to change color

      • Diatoms, raphidophytes, and dinoflagellates are representative groups

      • Different types of plankton produce different colors, such as reddish-brown and dark brown

    • Reported frequently in inner bays of western Japan, such as the Seto Inland Sea and Ariake Sea

    • Red tides increased dramatically during the period of rapid economic growth due to the discharge of nutrients (nitrogen and phosphorus) and organic matter
      • The number of outbreaks has been decreasing due to stricter effluent standards

    • Causing damage to fisheries

      • Fish become unable to breathe due to gill damage
      • Oxygen is consumed to break down the plankton, resulting in oxygen deprivation
      • Toxins produced by the plankton act

    • This red tide was observed in the open sea, not in closed sea areas, and has never been reported in Japan, has it?

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    Overview of red tide in the Pacific coast of east Hokkaido, Japan, Occurring in 2021

    • Red tide outbreak was confirmed in Akkeshi Bay on September 13, 2021
      • Discovered by associate professor ISADA of Akkeshi Marin Station, Hokkaido University
    • Confirmation that the dominant species is Karenia selliformis（Iwataki et al., 2021）
      • This is the first report of red tide in Karenia selliformis in Japan

    • Extensive damage to fisheries

      • As of December 10, 2021, Hokkaido reported a total of 8.1 billion yen in damage, including 2,800 tons of sea urchins and 28,000 salmon
      • The Kushiro Fisheries Research Institute, Hokkaido Research Organization, Fisheries Research Department discovered the mass death of a benthic organism, “sipunculids” on the seafloor 24 km off the coast of Tokachi at a depth of 130 m (Hokkaido Shimbun Press, December 10, 2021)
    • According to the announcement by the Hokkaido Research Organization, Fisheries Research Department, the red tide is likely to have almost ended as of November 22 (Central Fisheries Research Institute, Hokkaido Research Organization, Fisheries Research Department)
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    Red tide as seen from satellites

    Data from the satellite Global Change Observation Mission - Climate “SHIKISAI” of JAXA can be used to determine temporal changes in the distribution of chlorophyll, an indicator of the amount of phytoplankton on the ocean surface.

    As a result, it appears that seawater with high phytoplankton content is flowing from around the Northern Territories to the east Hokkaido coast. This suggests that the red tide has moved with the flow of the cold current Oyashio Current.

    9月4日のクロロフィル画像September 4, 2021

    9月16日September 16, 2021

    10月9日October 9, 2021

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    Related environment

    • Red tide occurred in the waters around Kamchatka Peninsula, Russia, in late September 2020
      • The dominant species is Karenia selliformis
      • Genetic information of this K. selliformis are 100% identical genetically with K. selliformis of the 2021 Hokkaido red tide (Iwataki et al., 2021)
      • A part of the red tide may reach the sea area around the Northern Territories in a few months by riding on the Oyashio Current (Kuroda et al., 2021)

    • Ocean heat waves occurred over a wide area of the Pacific Ocean, including around Hokkaido, Japan, in July and August 2021

      • This is the largest ocean heat wave on record with water temperatures rising max 5℃ higher than normal
      • Causal relationship between ocean heat waves and red tide outbreaks is unknown
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    Red tides in Hokkaido in the past


    Time of emergence Sea areaCausal species Estimated cause of occurrence
    September, 1972 off the mouth of the Tokachi River dinoflagellates the genus Gymnodinium

    After heavy rainfall, the river outflow was followed by a series of calm days, which allowed river-derived nutrients to accumulate near the sea surface.
    September, 1983 Urahoro-cho to Erimo-chodinoflagellates the genus Gymnodinium same as above

    September, 1985

    		 off the mouth of Tokachi River to Taiki Fisheries Port dinoflagellates the genus Gymnodinium and Prorocentrum same as above
    September, 1986 off the mouth of Rekifune River to mouth of Toyoni River raphidophytes Heterosigma akashiwo same as above
    October to November, 2015 Hakodate Bay dinoflagellates Karenia mikimotoi

    A part of the red tide that occurred on the Japan Sea side, such as Kyushu and San-in migrated on the warm Tsushima Warm Current and proliferated.
    July, 2016 Hakodate Bay raphidophytes Heterosigma akashiwo
    July, 2018 Hakodate Bay raphidophytes Heterosigma akashiwo
    September to November, 2021 Pacific coast of east Hokkaido dinoflagellates Karenia selliformis