Effect of diatom abundance and biogenic silica availability on the population growth of tintinnid ciliates at Suruga Bay
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ORIGINAL ARTICLE
Effect of diatom abundance and biogenic silica availability on the population growth of tintinnid ciliates at Suruga Bay Nhan Van Dinh1,2 · Beatriz E. Casareto1 · Mohan P. Niraula3 · Keita Toyoda1 · Aussanee Meekaew1 · Yoshimi Suzuki1 Received: 23 March 2020 / Revised: 5 October 2020 / Accepted: 8 October 2020 © The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. 2020
Abstract The effects of diatom abundance and biogenic silica (BSi) deposition on the population growth of tintinnid ciliates were investigated using incubations of sub-surface waters (10 m depth) of Suruga Bay, Japan in April and November 2018. Seawater for incubation was pre-filtered using a 200-µm mesh to remove mesozooplankton grazers. Initial concentrations of dissolved inorganic nitrogen were similar in both seasons, but silicic acid and phosphate were higher in April than in November. This allowed us to observe the growth of planktonic communities under varied silicic acid availability and explore the effects of BSi accumulation and food availability on the growth of tintinnids. Phytoplankton blooms dominated by diatoms formed in both, April and November incubations, but their biomass was higher in April than in November, demonstrating the effects of nutrients, particularly silicic acid, on diatom growth. The BSi concentration increased in both incubations but was higher in April than in November, confirming the effects of diatom abundance and size on BSi deposition. Tintinnid biomass also increased in both incubations but was higher in April than in November, showing that the biomass of tintinnid was affected by the BSi concentration. Species composition of diatoms affected the species composition of tintinnids by providing selected material for the construction of their lorica. Moreover, the results showed that the food supply mainly provided by piconanoflagellates via microbial loop and detritus may limit tintinnids’ population growth in natural planktonic ecosystems and this demonstrates tintinnids’ role as top predators in the microbial loop Keywords Tintinnid ciliates · Biogenic silica · Silicic acid · Diatom biomass · Tintinnids lorica · Nutrient availability · Pico-nanoflagellates · Bacteria
1 Introduction Tintinnid ciliates are essential components of the microzooplankton in the marine ecosystem living in shallow ocean waters worldwide (Dolan et al. 2013; Sherr and Sherr 2007; Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10872-020-00569-z) contains supplementary material, which is available to authorized users. * Beatriz E. Casareto [email protected] 1
Environment and Energy Systems, Graduate Schools of Science and Technology, Shizuoka University, Shizuoka 422‑8529, Japan
2
Institute of Marine Environment and Resources (IMER), Vietnam Academy of Science and Technology (VAST), 246 Da Nang St., Haiphong, Vietnam
3
Tribhuvan University, Trichandra Campus, Kathmandu, Nepal
Uye et al. 2000; Weisse 2017). They range in size f
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