Autumn to spring microbial community in the northern Baltic Sea: temporal variability in bacterial, viral and nanoflagellate abundance during the cold-water season

Abstract

Marine microbial communities undergo drastic changes during the seasonal cycle in high latitude seas. Despite the dominance of microbial biomass in the oceans, comprehensive studies on the seasonal changes of microbial plankton during the complete winter period are lacking. To study the seasonal variation in abundance of the microbial community, water samples were collected weekly in the Northern Baltic Sea from October to May. During ice cover from mid-January to April, samples from the sea ice and the underlying water were taken in addition to the water column samples. Abundances of bacteria, virus-like particles, nanoflagellates, and chlorophyll a concentrations were measured from sea ice, under-ice water, and the water column, and examined in relation to environmental conditions. All studied organisms had clear seasonal changes in abundance, and the sea-ice microbial community had an independent wintertime development compared to the water column. Bacteria were observed to have a key role in the biotic interactions in both ice and the water column, and the dormant period during the cold-water months (October–May) was limited to before ice formation. Our results provide the first insights into the temporal dynamics of bacteria and viruses during the whole cold-water season (October–May) in coastal high latitude seas, and demonstrate that changes in the environmental conditions are likely to affect bacterial dynamics and have implications on trophic interactions.

Cold-Active Shewanella glacialimarina TZS-4T nov. Features a Temperature-Dependent Fatty Acid Profile and Putative Sialic Acid Metabolism

“…This suggests that sialic acid metabolism might instead be linked to nutrient utilization. Phytoplankton and fungi tend to be prevalent in the Baltic Sea during summer times when the temperature is above 10°C (Kaikkonen et al, 2020). These eukaryotes have peripheral sialic acid that could act as a stimulus for sialic acid metabolising bacteria to exploit this resource.…”

Taxonomically and Functionally Distinct Ciliophora Assemblages Inhabiting Baltic Sea Ice

“…To separate this drift from trends induced by environmental or biotic processes in the time series [ 36 ], asymmetric eigenvector maps (AEMs) and local contributions to beta diversity (LCBD) were generated, following Appendix S2 of Legendre and Gauthier [ 48 ]. Values of sea-ice and water temperature, salinity, nutrients, algal biomass and chlorophyll a were taken from Enberg et al [ 36 ] and values of bacterial abundance and productivity from Kaikkonen et al [ 49 ]. Irradiance and air temperature were retrieved from the Photovoltaic Geographical Information System ( https://ec.europa.eu/jrc/en/pvgis ) 21 September 2020, and a weekly average (7-day period prior to the sampling time) of the daily irradiance and air temperature was calculated for each sampling time.…”

Seasonality of top‐down control of bacterioplankton at two central Red Sea sites with different trophic status

“…Heterotrophic protists and viruses are deemed as the most significant factors causing bacterioplankton losses in the ocean (Giorgio et al, 1996; Suttle, 2007) through size‐selective grazing and host‐specific lysis activities, respectively, regulating the flow of energy and organic matter through the planktonic food web (Liu et al, 2015). Attempts have been made to determine the impact of top‐down control on prokaryotic communities in both marine and fresh water ecosystems [e.g., the coastal Mediterranean Thau lagoon in Bouvy et al, 2011; or groups of temperate lakes in France (Ram et al, 2014)], suggesting that the relative impact of heterotrophic nanoflagellates (HNFs) and viruses on bacterioplankton communities can vary in different environments, often resulting in spatial (e.g., Kopylov et al, 2021) and temporal (e.g., Kaikkonen et al, 2020) variability. Tsai et al (2013) suggested that grazing by HNF was the main source of bacterioplankton mortality during summertime, while viral lysis was responsible for most bacterial losses during the colder months in the subtropical W Pacific Ocean.…”