Opening the “black box” of the Polar night

Opening the “black box” of the Polar night

Top image: PhD candidate Miriam Marquardt on fieldwork. Photo: Malin Daase.

Miriam Marquardt has investigated the community composition, seasonality and diversity of marine microbial eukaryotes in Svalbard waters. Marquardt will defend her PhD thesis at UNIS on Tuesday 18 October.

14 October 2016
Press release from the University Centre in Svalbard (UNIS) and UiT The Arctic University of Norway

Microbial eukaryotes are critically important for the functioning of marine ecosystems. In Arctic waters, where marine planktonic cyanobacteria are infrequent, microbial eukaryotes are the predominant primary producers. The ongoing changes in the Arctic reflected by sea-ice retreat, freshening of the ocean and increased stratification may favour smaller protists in the future and that will potentially alter production and downward flux.

In spite of their importance, our knowledge of the diversity, seasonality and fate of pico- and nanosized eukaryotic plankton is still limited in the Polar regions, especially during the Polar night period. High-Arctic regions are characterized by extreme seasonality in light conditions, with 24 hours of sunlight in summer giving way to several months of complete darkness in winter.

Sampling techniques
Molecular tools are now available for identifying even the smallest protist species. To investigate microbial eukaryotes in Svalbard waters, Miriam Marquardt applied two sampling approaches:

(1) Spatial sampling at multiple locations around West Spitsbergen to study the distribution of two small key-phototrophs (Micromonas pusilla and Phaeocystis pouchetii) during the polar night. PCR screening with specific primers was used to overcome the difficulty of identifying these small flagellates in low-biomass winter samples.

(2) High-resolution temporal sampling (December 2011 to December 2012) at the Isfjorden-Adventfjorden time series station (IsA, West Spitsbergen) was conducted to investigate the succession and diversity of small protists and to determine their contribution to the vertical carbon flux. The community composition of suspended microbial eukaryotes (two size fractions: 0.45 – 10 μm and > 10 μm) from four different depths (5, 15, 25 and 60 m) was determined using 454 sequencing of the 18S V4 region amplified from both DNA and RNA. Additionally, microbial eukaryotes (> 0.45 μm) were sampled from short-time sediment traps (20, 30, 40 and 60 m) to study their contribution to the vertical flux. Hydrographical profiles and in situ environmental conditions were recorded at all stations.

Miriam Marquardt on fieldwork

Miriam Marquardt collecting samples. Photo: D. Freese

Strong seasonal shifts of the community composition, species richness and photosynthetic biomass were observed in Adventfjorden. The winter and early-spring communities were more diverse than the spring and summer/autumn communities. Small Gyrodinium species were predominant in both DNA and RNA libraries of the suspended material throughout the year, and in the trap material. The Arctic Micromonas ecotype was most abundant in the early bloom and fall periods at IsA, but was widely distributed and active at almost all locations and depths around Svalbard. Also Phaeocystis pouchetii was widespread during the polar night, and blooming from mid to end of May at the IsA station.

Heterotrophs such as Marine Stramenopiles (MASTs), Picozoa and the parasitic Marine Alveolates (MALVs) displayed higher relative abundances in winter than in other seasons in Adventfjorden. Strategies such as kleptoplasty and parasitism might have helped certain species (e.g. Strombidium sp. and MALVs, respectively) to cope with unfavourable conditions at certain times of the year. Smaller cells (< 10 μm) contributed more to the vertical flux during autumn and winter, possibly due to increased flocculation and ballasting.

In contrast, larger and more typical spring bloom taxa (e.g. diatoms) dominated both the water column and the sedimented material in spring. In March an advective event, which replaced cold and less saline Local Water with warm and saline Transformed Atlantic Water was potentially responsible for a change in the IsA community composition.

The combined use of RNA and DNA data was of large benefit when opening the ”black box” of the polar night, revealing that the Arctic winter protist communities are active and more diverse than expected. Molecular tools not only revealed novel taxa contributing to the vertical export, but also suggested new mechanisms for vertical export demonstrated by parasite-host induced transport. Together, these results emphasize the extreme seasonality of Arctic microbial communities driven by the environment (e.g. light regime, nutrient availability), but also point to the necessity of a thorough knowledge of hydrography to fully understand their succession, variability and fate.

Dissertation
Miriam Marquardt will defend her PhD thesis, entitled “Marine microbial eukaryotes in Svalbard waters: Seasonality, community composition and diversity” at UNIS on Tuesday 18 October at 16:15.

She will give a trial lecture entitled “Grazing patterns of the microbial food web in the polar sea” at 15:00 the same day.

Both lectures will take place in the auditorium “Lassegrotta”.

Miriam Marquardt

Miriam Marquardt.

About the candidate:
Miriam Marquardt, born 1984 in Henstedt-Ulzburg, Germany, studied biology at the Christian-Albrechts-University in Kiel, Germany. During her studies, she was an Erasmus student in Tromsø (2006-07) and had the opportunity to join a research cruise around Svalbard. Fascinated by the Arctic, she wrote her master thesis about ice fauna, before moving to Longyearbyen to start her PhD work at UNIS and UiT in 2012.
She is especially interested in organisms which cannot be seen with bare eyes (such as protists, ice fauna and zoo plankton), seasonal studies and biological systems.

Contact information:
E-mail: miriamm@unis.no
Phone: +47 975 67 641
Web: http://www.mare-incognitum.no/index.php/microfun

 

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