Unprecedented Outbreak of Harmful Algae in Pacific Coastal Waters off Southeast Hokkaido, Japan, during Late Summer 2021 after Record-Breaking Marine Heatwaves

Round 1

Reviewer 1 Report

It is appreciable that the first occurrence of Karenia selliformis bloom observed after "Heatwaves" in the north Pacific and its potential origins are reported. However, following aspect should be discussed.

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• The author(s) discussed the origin of the HABs, focusing only on the known occurrence areas (east coast of Kamchatka and the Japan Sea), but I think it is necessary to discuss also the Okhotsk Sea which has suitable oceanographic condition for mixotrophic dinoflagellates in summer but has little information on HABs. Basically, the North Pacific, the Okhotsk Sea, and the Japan Sea should be considered equally as the origin of HABs. For example, Figure 10 showing the larger number of the particles were estimated to be transported from the Okhotsk Sea than the north Pacific near Kamtchatka. Although there is little previous information on HABs in the Okhotsk Sea, it is undeniable that K. selliformis may have increased as in the North Pacific. To evaluate possibilities fairly as the origin of HABs, it would be better to provide some more prospective experiments as Appendix; from the Japan Sea (e.g. west coast of Aomori pref.) and the Okhotsk Sea (e.g. east coast of central Sakhalin).

• Regarding the assumption of particle retention in the discussion, it is better to refer to Shimada (2021)

http://www.hro.or.jp/list/fisheries/marine/att/kenpou1001_akasio.pdf

 and note that the red tide occurred in the autumn in the 1970-1980s in the eastern Hokkaido area.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper by Kuroda and colleagues addresses the possible sources and drivers of a sudden harmful algae bloom near Hokkaido island.

The paper is generally well written and I have only minor comments which I have made on the attached annotated PDF.

One thing that I want to stress out is the use of the term "experiments" for the particle tracking simulations. There is a difference between simulations and physical experiments and therefore, to prevent misleading the readers, the authors should use simulations. 

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

The results of this original paper  are interesting  for all phytoplankton community, because reveals models for forecasting of the HABs blooms  and can also be applied in another marine areas . Congratulations for design of the paper and discussion of the these very important problems.

Author Response

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Author Response File: Author Response.pdf