Seasonal and Interannual Changes in Ciliate and Dinoflagellate Species Assemblages in the Arctic Ocean (Amundsen Gulf, Beaufort Sea, Canada)

Abstract

Recent studies have focused on how climate change could drive changes in phytoplankton communities in the Arctic. In contrast, ciliates and dinoflagellates that can contribute substantially to the mortality of phytoplankton have received less attention. Some dinoflagellate and ciliate species can also contribute to net photosynthesis, which suggests that species composition could reflect food web complexity. To identify potential seasonal and annual species occurrence patterns and to link species with environmental conditions, we first examined the seasonal pattern of microzooplankton and then performed an in-depth analysis of interannual species variability. We used high-throughput amplicon sequencing to identify ciliates and dinoflagellates to the lowest taxonomic level using a curated Arctic 18S rRNA gene database. DNA-and RNA-derived reads were generated from samples collected from the Canadian Arctic from November 2007 to July 2008. The proportion of ciliate reads increased in the surface toward summer, when salinity was lower and smaller phytoplankton prey were abundant, while chloroplastidic dinoflagellate species increased at the subsurface chlorophyll maxima (SCM), where inorganic nutrient concentrations were higher. Comparing communities collected in summer and fall from 2003 to 2010, we found that microzooplankton community composition change was associated with the record ice minimum in the summer of 2007. Specifically, reads from smaller predatory species like Laboea, Monodinium, and Strombidium and several unclassified ciliates increased in the summer after 2007, while the other usually summer-dominant dinoflagellate taxa decreased. The ability to exploit smaller prey, which are predicted to dominate the future Arctic, could be an advantage for these smaller ciliates in the wake of the changing climate.

Culturable diversity of Arctic phytoplankton during pack ice melting

“…strains that originated from the ice are not closely related to any polar strain or environmental sequence, potentially representing a new cold-adapted genotype. The retrieval of only one dinoflagellate species, Biecheleria cincta (previously Woloszynskia (Balzano et al, 2012) is at odds with the known diversity of dinoflagellates in the Arctic (Bachy et al, 2011; Onda et al, 2017) and especially in Baffin Bay (Lovejoy et al, 2002). Another extensive Arctic culture isolation effort yielded a similar result (Balzano et al, 2012), indicating the need for alternative isolation methods to overcome this bias.…”

“…The most commonly reported genera include Cylindrotheca , Fragilariopsis , Navicula , Nitzschia and Pseudo-nitzschia (Katsuki et al, 2009; Leeuwe et al, 2018; Poulin et al, 2011). In contrast to diatoms and small flagellates that present a strong seasonal signal, dinoflagellates are prevalent throughout the year (Comeau et al, 2011; Marquardt et al, 2016), although some taxa vary seasonally (Onda et al, 2017).…”

Biodiversity and Species Change in the Arctic Ocean: A View Through the Lens of Nares Strait

“…The differences in hydrography between the North Water Polynya and the Nares Strait system are substantial and as surface productivity moves north there is no a priori reason to expect a simple northward displacement of microbial community structure between the two systems. Microbial eukaryotes track their water mass of origin but are subject to differing degrees of selective pressures within their local environment (Monier et al, 2015;Onda et al, 2017). However, little to nothing is known about the species composition of phytoplankton and other microbial eukaryotes within Nares Strait and whether they are similar to species previously reported from the North Water or elsewhere in the Arctic.…”

Diversity and biogeography of SAR11 bacteria from the Arctic Ocean

“…The SAR11 (Pelagibacterales) group accounts for roughly 30% of bacteria in the ocean surface and 25% of mesopelagic bacteria [1][2][3]. High phylogenetic diversity and divergence into total, 6 distinct phylotypes were evident from ITS sequences ( Figure 1C), from all major clades 174 S1, S2, and S3 ( Figure 1C, Figure 2A-D).…”

“…Sample depth was determined during the downward casts, to ensure that target water masses were sampled, with the DCM identified from the Chl a fluorescence and PWW centered on a salinity of 31. Nutrient samples and Chl a were collected directly from the Niskin bottles and analysed on board as previously described[1]. Consistency of the targeted and actual sampling depths were verified by bottle salinities analyzed onboard using a Guideline Portasal and IAPSO standard seawater[2], while dissolved oxygen (DO) was determined by Winkler-based titration (Kit B, Scripps Institute of Oceanography, USA).…”