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Species-specific monitoring of Skeletonema blooms in the coastal waters of Ariake Sound, Japan

Kazuhiro Yoshida, Hiroshi Ota, Takuya Iwanaga, Aiko Yoshitake, Takayuki Mine, Mana Omura, Kei Kimura*

*Corresponding author:

ABSTRACT: Skeletonema is a cosmopolitan diatom observed in coastal waters, which forms extensive blooms, largely underpining coastal ecosystems and fisheries. Recent revisions to Skeletonema’s phylogeny have shown multiple pseudocryptic species within the type species S. costatum. We developed a novel species-specific quantitative polymerase chain reaction (qPCR) method to track the annual dynamics of seven Skeletonema species, including the pseudocryptic species, in the coastal waters of Ariake Sound, Japan. Fortnight monitoring revealed that each Skeletonema species had different seasonality and patterns. The significant findings related to: (1) the species-specific ecological strategies and (2) the ecophysiology of the five pseudocryptic species assigned as S. costatum (sensu lato). Three Skeletonema species (S. costatum (sensu stricto), S. menzelii, and S. tropicum) formed blooms in summer, while the copy number of other species increased in winter (S. ardens, S. dohrnii/marinoi, S. grevillei, and S. japonicum). Bloom dynamics also differed among species, with either single intense bloom events or sustained moderate blooms. Summer species bloomed successively under the highly-dynamic summer conditions (high freshwater input and anticyclonic tropical typhoons). By contrast, in winter, multi-species blooms were observed by low sea surface temperature and solar insolation. The single-peak species intensely bloomed during an ephemeral optimal time whereas others sustained their biomass in a pax after intense blooms. Our in situ species-specific monitoring study connects ex situ physiology and in situ distributions, highlighting the diverse ecophysiology within this cosmopolitan diatom genus.