From October 6-12, 2021, 1 L of surface
seawater was sampled by the Training Ship Ushio-Maru (179 tons), which is
attached to the Faculty of Fisheries Sciences of Hokkaido University, at a
total of 32 points between the west coast of Cape Erimo and offshore Akkeshi.
Water samples were fixed by adding glutaraldehyde to reach a final
concentration of 1%, and the number of phytoplankton cells was counted.
Chlorophyll a, a pigment contained in phytoplankton, was also measured. To
clarify the conditions for high density of the red tide-causing algae K. selliformis
in the field, a generalized linear model was used to analyze environmental
factors: water temperature, salinity, nitrate, nitrite, ammonium, phosphate,
and silicate concentrations as independent variables, and K. selliformis
cell number density as the objective variable. After creating a similarity
matrix based on cell number density data for each species or genus of
unicellular organisms, a dendrogram was created using the mean linkage method,
and phytoplankton communities were separated by arbitrary similarity levels.
The GCOM-C "Shikisai," a climate change observation satellite
provided by JAXA, was used to evaluate the horizontal distribution of sea
surface temperature and chlorophyll a during the study period.
