Rapid succession drives spring community dynamics of small protists at Helgoland Roads, North Sea.

Bernhard M Fuchs,Alexandra C Kraberg,Laura Käse,Karen H Wiltshire,Maarten Boersma,Katja Metfies,Pim A A Sprong,Stefan Neuhaus

doi:10.1093/plankt/fbaa017

Abstract

The dynamics of diatoms and dinoflagellates have been monitored for many decades at the Helgoland Roads Long-Term Ecological Research site and are relatively well understood. In contrast, small-sized eukaryotic microbes and their community changes are still much more elusive, mainly due to their small size and uniform morphology, which makes them difficult to identify microscopically. By using next-generation sequencing, we wanted to shed light on the Helgoland planktonic community dynamics, including nano- and picoplankton, during a spring bloom. We took samples from March to May 2016 and sequenced the V4 region of the 18S rDNA. Our results showed that mixotrophic and heterotrophic taxa were more abundant than autotrophic diatoms. Dinoflagellates dominated the sequence assemblage, and several small-sized eukaryotic microbes like Haptophyta, Choanoflagellata, Marine Stramenopiles and Syndiniales were identified. A diverse background community including taxa from all size classes was present during the whole sampling period. Five phases with several communities were distinguished. The fastest changes in community composition took place in phase 3, while the communities from phases 1 to 5 were more similar to each other despite contrasting environmental conditions. Synergy effects of next-generation sequencing and traditional methods may be exploited in future long-term observations.

Highlights

Planktonic eukaryotic microbes as encompassed by the term “phytoplankton” represent a diverse array of plankton groups of all size classes including picoand nanoplankton
To check whether the spring of 2016 showed a typical phytoplankton community succession of diatoms followed by dinoflagellates as observed in the Long-Term Ecological Research (LTER), we used total diatom and total dinoflagellate counts and chlorophyll a measured by HPLC modified after Zapata et al (2000) from 1st March to 31st May
If we look at other heterotroph small-sized eukaryotic microbes like the MAST groups, which are not included in the LTER, we found a high amount of operational taxonomic unit (OTU), of which several were present in all samples and clustered within the biggest cluster

Summary

Introduction

Planktonic eukaryotic microbes as encompassed by the term “phytoplankton” represent a diverse array of plankton groups of all size classes including picoand nanoplankton. They comprise the most frequent autotrophic groups such as diatoms, coccolithophores, green algae and cyanobacteria, and dinoflagellates, which contain autotrophs, as well as heterotrophs and mixotrophs (Sournia et al, 1991; Simon et al, 2009). Primary producers are important as a food source for their consumers and for bacterial plankton, as bacteria can feed on their excretory products or internal storage compounds after cell death in the form of dissolved or particulate organic matter (Sherr and Sherr, 2002). Far, these are barely identifiable to species level by traditional microscopic methods because of their miniscule size and uniform morphology

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