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.
