Metabarcoding Reveals Temporal Patterns of Community Composition and Realized Thermal Niches of <i>Thalassiosira</i> Spp. (Bacillariophyceae) from the Narragansett Bay Long-Term Plankton Time Series
2020
Tatiana A. Rynearson | Sarah A. Flickinger | Diana N. Fontaine
Diatoms generate nearly half of marine primary production and are comprised of a diverse array of species that are often morphologically cryptic or difficult to identify using light microscopy. Here, species composition and realized thermal niches of species in the diatom genus <i>Thalassiosira</i> were examined at the site of the Narragansett Bay (NBay) Long-Term Plankton Time Series using a combination of light microscopy (LM), high-throughput sequencing (HTS) of the 18S rDNA V4 region and historical records. <i>Thalassiosira</i> species were identified over 6 years using a combination of LM and DNA sequences. Sixteen <i>Thalassiosira</i> taxa were identified using HTS: nine were newly identified in NBay. Several newly identified species have small cell diameters and are difficult to identify using LM. However, they appeared frequently and thus may play a significant ecological role in NBay, particularly since their realized niches suggest they are eurythermal and able to tolerate the >25 °C temperature range of NBay. Four distinct species assemblages that grouped by season were best explained by surface water temperature. When compared to historical records, we found that the cold-water species <i>Thalassiosira nordenskioeldii</i> has decreased in persistence over time, suggesting that increasing surface water temperature has influenced the ecology of phytoplankton in NBay.
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