Supplementary file 1_Phytoplankton and giant virus diversity during different monsoon seasons, a fish kill, and a saxitoxin episode in a eutrophic mariculture area.docx

In Bolinao, Philippines, intensive mariculture has led to diatom- or dinoflagellate-dominated HABs since the 2000s, raising risks of paralytic shellfish poisonings and fish kills. In the context of ongoing HAB monitoring and mitigation efforts, we investigated the overall phytoplankton community composition and co-occurring giant viruses during two seasons (Nov–Dec 2021 and Apr–May 2022).

Our sampling encompassed a saxitoxin episode lasting 2.5 months (April–June 2022), and a fish kill (May 15–16, 2022). We used a low-cost flow-through camera (PlanktoScope) and 18S rRNA gene amplicon sequencing to identify the dominant phytoplankton. Diatoms were numerically the dominant large eukaryotic algae during most of our time series, but we also detected the dinoflagellate Alexandrium sp., a known saxitoxin-producing alga, coincident with a toxin alert that resulted in a shellfish ban, even though it was not the dominant taxon.