1) Small lakes formed by thawing permafrost are typically heterotrophic due to high organic inputs, however analyses of 18S rRNA and pigments show a diverse and active photosynthetic community in these lakes. 2) Milne Fiord Epishelf Lake in the Canadian Arctic, dominated by the green algae Carteria, is a unique high latitude system threatened with extinction as the unstable ice shelf holding back its waters breaks up. 3) Monitoring of the protist community in the northern Canada Basin from 2005-2014 shows that diversity was exceptionally low in 2012 when sea ice retreat passed 80°N, the aim is to determine which taxa are driving this change.

1. 5) Diverse picophytoplankton found in
permafrost thaw lakes that are net heterotrophic
•Small lakes formed by thawing permafrost are typically heterotrophic
because of high organic inputs
•However, 18S rRNA amplicons combined with pigment analyses
show a diverse and active photosynthetic
•community
Aquatic protist communities in the midst of
environmental change: using 18S rRNA gene surveys to
identify diversity over time and space
Mary Thaler (mary.thaler.1@ulaval.ca) Sophie Crevecoeur, Nathalie Joli, Deo Onda,
Bérangère Péquin, Anna Przytulska-Bartosiewicz, Warwick Vincent, Connie Lovejoy
Introduction
•Protist communities are a central component of aquatic ecosystems, and their taxonomic structure is
sensitive to environmental change
•We use 18S rRNA gene surveys to capture such changes at a fine taxonomic scale, taking advantage of
high throughput techniques to include many taxa poorly sampled by classical methods
•Five projects from Arctic and temperate waters map the eukaryotic diversity through broad-scale changes
including ice regimes, seasonal wind patterns and permafrost thawing.
Take-home points
•18S rRNA gene surveys can uncover
profound changes in the protist
community in response to intrinsic and
environmental factors
•At high latitudes, recent rapid
environmental change requires urgent
study before its impact can be
understood
1.03Peridinium wierzejskiiDinoflagellate
1.00Chlorella sp.Chlorophyte
1.07Lemmermannia punctataChlorophyte
1.22Urosolenia eriensisDiatom
1.31Dinophyceae sp.Dinoflagellate
1.71Cryptomonas tetrapyrenoidosaCryptophyte
3.83CercozoaRhizaria
6.03Uroglena sp.Chrysophyte
8.65Stokesia vernalisCiliate
•The balance of
heterotrophic and
autotrophic activity is
important because it
determines CO2 flux to
the atmosphere
Nine most common taxa (>1%) in 18S rRNA data
from thaw lake SAS2A. Known photosynthetic
organisms are highlighted %
2) Unique high-latitude system threatened with
extinction
•Milne Fiord Epishelf Lake, on the northern coast of Ellesmere Island,
consists of 16 m of freshwater floating over seawater behind an ice
dam
•High throughput 18S rRNA gene sequencing shows that, unlike any
other fresh- or salt-water environment studied in the Canadian Arctic,
Milne Fiord is dominated by a genus of large
green microalgae, Carteria
•Potential break-up of
an increasingly
unstable ice shelf will
eventually lead to the
loss of the last epishelf
lake in the Arctic
•Aim is to describe this
system before it
vanishes, and to
understand associated
biological processes
•Changes in the diversity of the protist
community will have an impact at
multiple scales system scales with
ecosystem-wide consequences
1) Loss of protist diversity in the northern
Canada Basin during an ice minimum year
•Summer of 2012 saw unprecedented retreat of sea-ice, passing 80°N
latitude in the Canada Basin
•Overall diversity of 18S rRNA was exceptionally low for all taxa <3µm.
Ice chart showing minimum ice extent in
the Canada Basin in 2012. Red represents
>90% ice cover. Dashed line shows ice
extent in a “normal” year (2010)
Phylogenetic diversity in Canada Basin
samples (< 3 µm) was significantly lower
in 2012 than in other years.
•Future work is to determine which protist taxa are driving this change
and how this will impact biological processes in the water column
Contact: Deo.Onda@takuvik.ulaval.ca Contact: mary.thaler.1@ulaval.ca
3) Nine years of monitoring the protist
community in Northern Baffin Bay, 2005–2014
•Pico-sized (< 2µm) eukaryotes are increasingly dominant in the
Beaufort Sea in response to greater stratification and nutrient
limitations
Arctic ecotypes of small green
algae, such as Micromonas,
may change in distribution
•The aim of the present study is to
describe interannual changes at a
fine taxonomic scale
•Monitoring period includes years
of dramatic sea-ice loss
•It is unknown how
this trend will
manifest in an area
of complex
hydrography like
Baffin Bay
Warm Greenland
current
Cold Arctic
current
West-east temperature section of Baffin Bay showing
fronts between currents
x
Contact: Nathalie.Joli@takuvik.ulaval.ca
4) High wind events plus top-down control by
dinoflagellates modulate picophytoflagellates in
the Magdalen Islands
•Protist community composition was tracked over summer and
autumn in a coastal lagoon using high-throughput sequencing of
the 18S DNA gene
•Windy periods appear to be unfavourable for dinoflagellates,
releasing the phytoflagellates from predation control
WIND
dinoflagellates
phytoflagellates
Contact: berangere.pequin.1@ulaval.ca
•Taxonomic composition is
significant for local
aquaculture, since dinoflagellates are the
main food source for farmed mussels
Contact: anna.przytulska.1@ulaval.ca