Changes in the Abundance and Taxonomic Composition of Benthic Heterotrophic Protists from Atlantic Sublittoral to Deep-Sea Sediments

Manon Hohlfeld,Hartmut Arndt

doi:10.3390/d14030164

Abstract

Protists are the most diverse eukaryotes on our planet and metabarcoding has revealed an enormous diversity even from deep-sea environments. A range of different species has also been isolated from the deep sea and some have proven able to survive and even grow under deep-sea conditions. However, little is known about how the community structure of benthic protists changes from sublittoral down to abyssal depths. This is especially important regarding island and seamount communities which are surrounded by deep-sea areas potentially isolating them. Using a combination of live-counting and cultivation techniques, we investigated the abundance and taxonomic composition of benthic protist communities in sediments from sublittoral to abyssal depths around three islands and two seamounts of the Azores’ archipelago in the North Atlantic. Protist abundance decreased significantly and community composition changed with increasing depth. While some species were found at all depths, others were only detected in sublittoral or lower bathyal depths, indicating that some benthic taxa are limited in their distribution to a certain depth, whereas others are also present at the deep-sea floor. The proportion of unidentified specimens increased with depths pointing towards a high number of so far undetected species in the deep-sea realm.

Highlights

Protists are the most diverse and dominant eukaryotes on our planet [1,2,3]
202 different taxa were identified during live-counting of sediment suspensions comprising nanofauna (2–20 μm cell length), microfauna (20–200 μm cell length), microphytobenthos, and meiofauna
As the sample volume used was not suitable for a representative analysis of the abundance of meiofaunal organisms, they were not included in further analyses, but more information on the benthic meiofauna analyzed during the cruise can be found in [26]

Summary

Introduction

Protists are the most diverse and dominant eukaryotes on our planet [1,2,3]. Due to their broad functional diversity and their role as nutrient remineralizers, heterotrophic protists are known to represent a crucial component of the global carbon cycle and play an important role for ecosystem functioning [4,5]. As primary consumers of bacteria, heterotrophic protists remineralize carbon and form a link to higher trophic levels in marine ecosystems While these processes are well studied for marine surface waters [6,7,8], they are neither well studied nor understood for the deep-sea floor [9]. The vast diversity of protistan genotypes at the deep-sea floor was revealed in more recent years by metabarcoding studies [13,14,15,16] While these high-throughput-sequencing techniques can generate massive amounts of data and enable the investigation of the diversity and distribution of protists [17], they lack morphological data, as well as firm data on the abundance and biomass of organisms, which are necessary to understand the structure and functioning of microbial foodwebs and their trophodynamics. Cultivation-based approaches allow for detailed investigations on the morphology, the autecology, and the phylogeny of single species and can be used to estimate the diversity and abundance of cultivable taxa [18,19]

Methods

Results

Discussion

Conclusion