Diverse eukaryotic phytoplankton from around the Marquesas Islands documented by combined microscopy and molecular techniques

Oceanic phytoplankton serve as a base for the food webs within the largest planetary ecosystem. Despite this, surprisingly little is known about species composition, function and ecology of phyto-plankton communities, especially for vast areas of the open ocean. In this study we focus on the mar-ine phytoplankton microflora from the vicinity of the Marquesas Islands in the Southern Pacific Ocean collected during the Tara Oceans expedition. Multiple samples from four sites and two depths were studied in detail using light microscopy, scanning electron microscopy, and automated confocal laser scanning microscopy. In total 289 taxa were identified, with Dinophyceae and Bacillariophyceae con-tributing 60% and 32% of taxa, respectively, to phytoplankton community composition. Notwithstand-ing, a large number of cells could not be assigned to any known species. Coccolithophores and other flagellates together contributed less than 8% to the species list. Observed cell densities were generally low, but at sites of high autotrophic biomass, diatoms reached the highest cell densities (1.26 x 104 cells L-1). Overall, 18S rRNA metabarcode-based community compositions matched microscopy-based estimates, particularly for the main diatom taxa, indicating consistency and complementarity between different methods, while the wide range of microscopy-based methods permitted several unknown and poorly studied taxa to be revealed and identified. & COPY; 2023 Elsevier GmbH. All rights reserved.

Automated summary

This study investigates the marine phytoplankton microflora from the vicinity of the Marquesas Islands in the Southern Pacific Ocean. A total of 289 taxa were identified, with Dinophyceae and Bacillariophyceae making up the majority. Coccolithophores and other flagellates contributed less than 8% to the species list. The microscopy-based methods revealed several unknown and poorly studied taxa.