Abstract
The Thessaloniki Bay is a eutrophic coastal area which has been characterized in recent years by frequent and intense phytoplankton blooms and red tides. The aim of the study was to investigate the underexplored diversity of marine unicellular eukaryotes in four different sampling sites in Thessaloniki Bay during a year of plankton blooms, red tides, and mucilage aggregates. High-Throughput Sequencing (HTS) was applied in extracted DNA from weekly water samples targeting the 18S rRNA gene. In almost all samples, phytoplankton blooms and/or red tides and mucilage aggregates were observed. The metabarcoding analysis has detected the known unicellular eukaryotic groups frequently observed in the Bay, dominated by Bacillariophyta and Dinoflagellata, and revealed taxonomic groups previously undetected in the study area (MALVs, MAST, and Cercozoa). The dominant OTUs were closely related to species known to participate in red tides, harmful blooms, and mucilage aggregates. Other OTUs, present also during the blooms in low abundance (number of reads), were closely related to known harmful species, suggesting the occurrence of rare taxa with potential negative impacts on human health not detectable with classical microscopy. Overall, the unicellular eukaryote assemblages showed temporal patterns rather than small-scale spatial separation responding to the variability of physical and chemical factors.
Highlights
During the past decade, the advancement of High-Throughput Sequencing (HTS) technologies have provided unprecedented insights into the diversity [1,2,3,4,5], spatial community composition [6,7,8], temporal patterns [9,10,11,12], and functional and ecological processes affected by marine unicellular eukaryotes [9,13,14]
The seawater temperature during the year of the study ranged from 9.6 ◦ C on 24 January 2018 at the White Tower (WT) site, to 29.7 ◦ C on 09 August 2017 at the same site (Supplementary Figure S1)
High values were recorded for all nutrients on 28 July 2017 at WT and Music Hall coast (MH) sites, 20 September 2017 in all sites, and 10 January 2018 in WT
Summary
The advancement of High-Throughput Sequencing (HTS) technologies have provided unprecedented insights into the diversity [1,2,3,4,5], spatial community composition [6,7,8], temporal patterns [9,10,11,12], and functional and ecological processes affected by marine unicellular eukaryotes [9,13,14]. Diversity 2020, 12, 114 in unicellular eukaryotic communities have been explored, using classical and modern ecological tools [17,18]. It is evident that the plethora of the genetic and ecological information produced provide a better understanding of marine global ecosystem processes [19,20]. There is an increase in the attention of marine microbiologists thanks to the development of HTS tools
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