Insights into global diatom distribution and diversity in the world’s ocean

Abstract

Diatoms (Bacillariophyta) constitute one of the most diverse and ecologically important groups of phytoplankton. They are considered to be particularly important in nutrient-rich coastal ecosystems and at high latitudes, but considerably less so in the oligotrophic open ocean. The Tara Oceans circumnavigation collected samples from a wide range of oceanic regions using a standardized sampling procedure. Here, a total of ∼12 million diatom V9-18S ribosomal DNA (rDNA) ribotypes, derived from 293 sizefractionated plankton communities collected at 46 sampling sites across the global ocean euphotic zone, have been analyzed to explore diatom global diversity and community composition. We provide a new estimate of diversity of marine planktonic diatoms at 4,748 operational taxonomic units (OTUs). Based on the total assigned ribotypes, Chaetoceros was the most abundant and diverse genus, followed by Fragilariopsis, Thalassiosira, and Corethron. We found only a few cosmopolitan ribotypes displaying an even distribution across stations and high abundance, many of which could not be assigned with confidence to any known genus. Three distinct communities from South Pacific, Mediterranean, and Southern Ocean waters were identified that share a substantial percentage of ribotypes within them. Sudden drops in diversity were observed at Cape Agulhas, which separates the Indian and Atlantic Oceans, and across the Drake Passage between the Atlantic and Southern Oceans, indicating the importance of these ocean circulation choke points in constraining diatom distribution and diversity. We also observed high diatom diversity in the open ocean, suggesting that diatoms may be more relevant in these oceanic systems than generally considered. biodiversity | diatoms | metabarcoding | Tara Oceans | choke points

Diatom Transcriptional and Physiological Responses to Changes in Iron Bioavailability across Ocean Provinces

“…For our study, we focused on the changes in gene expression patterns between two dominant taxa across all sites-the pennate diatom Pseudo-nitzschia and the centric diatom Thalassiosira. These two taxa were classified by the Tara Oceans circumnavigation expedition to be two of the eight most abundant diatom genera in the global ocean (Malviya et al, 2016). Given the large amount of genetic and physiological variation observed between major diatom groups (Bowler et al, 2008;Sutak et al, 2012;Alexander et al, 2015), differences in molecular responses to changing Fe availabilities across the NE Pacific Ocean and CUZ were anticipated.…”

A Consumer's Guide to Satellite Remote Sensing of Multiple Phytoplankton Groups in the Global Ocean

“…In addition to HPLC pigments that so many of these approaches are validated upon, training datasets also need to include unambiguous metrics of community composition that include particle size distribution and taxonomy (from imaging technologies) (Bracher et al, 2015). Exploiting compilations of abundance and biomass (Leblanc et al, 2012) and connections to genetically determined community composition (Malviya et al, 2016) are potentially rich resources for expanding training and validation datasets. In addition, coincident optical [i.e., R rs (λ) and IOPs] observations will be highly important to connect to the signals observed by satellite radiometers.…”

Under the canopy: Community-wide effects of invasive algae in Marine Protected Areas revealed by metabarcoding

“…In studies targeting particular groups of protists, this should guide the marker choice. For instance, the v4 and v9 regions of the 18S gene have been extensively used for protist metabarcoding in the marine realm (e.g., Pawlowski et al, 2011;Logares et al, 2014;Malviya et al, 2016), with different advantages and pitfalls (Stoeck et al, 2010;Pawlowski et al, 2011). The nature of the target group, marker variability, and completeness of databases should be carefully considered before undertaking any metabarcoding study.…”