Pre-bloom dynamics of the Subpolar North Atlantic microbial food web
The aim of this study was to investigate the microbial planktonic food web in the pre- bloom period of the Subpolar North Atlantic Ocean. Through repeated visits to the Icelandic Basin, Norwegian Basin, and on the Shetland Shelf in the period March 28th to May 1st, we recorded the abundance of all t...
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The University of Bergen
2013
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ftunivbergen:oai:bora.uib.no:1956/7536 2023-05-15T17:30:43+02:00 Pre-bloom dynamics of the Subpolar North Atlantic microbial food web Paulsen, Maria Lund 2013-02-18 11089446 bytes application/pdf https://hdl.handle.net/1956/7536 eng eng The University of Bergen https://hdl.handle.net/1956/7536 Copyright the author. All rights reserved Microbial food web Pre-bloom Pico eukaryotes Heterorophic nanoflagellates Bacteria Grazing Deep convection Subpolar North Atlantic 756213 Master thesis 2013 ftunivbergen 2023-03-14T17:39:20Z The aim of this study was to investigate the microbial planktonic food web in the pre- bloom period of the Subpolar North Atlantic Ocean. Through repeated visits to the Icelandic Basin, Norwegian Basin, and on the Shetland Shelf in the period March 28th to May 1st, we recorded the abundance of all the functional groups of both autotrophic and heterotrophic microbes. At the first visits, all stations were characterized by low concentrations of chlorophyll a (0.1-0.5 µg l^{-1}) and a low abundance of heterotrophic bacteria (2-3.4 × 10^5 cells ml^{-1}), heterotrophic nanoflagellates (22-84 cells ml^{-1}), ciliates (1-2 cells ml^{-1}), and heterotrophic dinoflagellates (0.1-0.3 cells ml^{-1}) within the upper mixed layer. Following the abundance of heterotrophic protists generally increased; 2- fold for bacteria and up to 5-fold for heterotrophic nanoflagellates. An initial dominance of pico eukaryotes within the phytoplankton community was observed in late winter. This was followed, however, by a significant decrease during the pre-bloom period, despite high nutrient concentrations and increasing light intensity. The decrease of pico eukaryote was concurrent with an increase of heterotrophic nanoflagellates, hence grazing pressure. The microbial trophic interactions were analysed further via grazing experiments, performed with water sampled at the Icelandic Basin. These revealed heterotrophic nanoflagellate removal rates of 10-20 % of bacterial standing stock d^{-1} and as high as 30- 50 % of the standing stock of pico phytoplankton d^{-1} in the euphotic zone. We conclude that heterotrophic nanoflagellates in the pre-bloom can satisfy up to half of their carbon demand by herbivory, and thus the strong focus of heterotrophic nanoflagellates' role, as being mainly bacterivorous, should be revised. We document that the pre-bloom is a productive period with carbon entering the ocean food web largely via the microbial food web. Thus, not only the seasonal changes of physical condition, but also the microbial dynamics ... Master Thesis North Atlantic University of Bergen: Bergen Open Research Archive (BORA-UiB) |
institution |
Open Polar |
collection |
University of Bergen: Bergen Open Research Archive (BORA-UiB) |
op_collection_id |
ftunivbergen |
language |
English |
topic |
Microbial food web Pre-bloom Pico eukaryotes Heterorophic nanoflagellates Bacteria Grazing Deep convection Subpolar North Atlantic 756213 |
spellingShingle |
Microbial food web Pre-bloom Pico eukaryotes Heterorophic nanoflagellates Bacteria Grazing Deep convection Subpolar North Atlantic 756213 Paulsen, Maria Lund Pre-bloom dynamics of the Subpolar North Atlantic microbial food web |
topic_facet |
Microbial food web Pre-bloom Pico eukaryotes Heterorophic nanoflagellates Bacteria Grazing Deep convection Subpolar North Atlantic 756213 |
description |
The aim of this study was to investigate the microbial planktonic food web in the pre- bloom period of the Subpolar North Atlantic Ocean. Through repeated visits to the Icelandic Basin, Norwegian Basin, and on the Shetland Shelf in the period March 28th to May 1st, we recorded the abundance of all the functional groups of both autotrophic and heterotrophic microbes. At the first visits, all stations were characterized by low concentrations of chlorophyll a (0.1-0.5 µg l^{-1}) and a low abundance of heterotrophic bacteria (2-3.4 × 10^5 cells ml^{-1}), heterotrophic nanoflagellates (22-84 cells ml^{-1}), ciliates (1-2 cells ml^{-1}), and heterotrophic dinoflagellates (0.1-0.3 cells ml^{-1}) within the upper mixed layer. Following the abundance of heterotrophic protists generally increased; 2- fold for bacteria and up to 5-fold for heterotrophic nanoflagellates. An initial dominance of pico eukaryotes within the phytoplankton community was observed in late winter. This was followed, however, by a significant decrease during the pre-bloom period, despite high nutrient concentrations and increasing light intensity. The decrease of pico eukaryote was concurrent with an increase of heterotrophic nanoflagellates, hence grazing pressure. The microbial trophic interactions were analysed further via grazing experiments, performed with water sampled at the Icelandic Basin. These revealed heterotrophic nanoflagellate removal rates of 10-20 % of bacterial standing stock d^{-1} and as high as 30- 50 % of the standing stock of pico phytoplankton d^{-1} in the euphotic zone. We conclude that heterotrophic nanoflagellates in the pre-bloom can satisfy up to half of their carbon demand by herbivory, and thus the strong focus of heterotrophic nanoflagellates' role, as being mainly bacterivorous, should be revised. We document that the pre-bloom is a productive period with carbon entering the ocean food web largely via the microbial food web. Thus, not only the seasonal changes of physical condition, but also the microbial dynamics ... |
format |
Master Thesis |
author |
Paulsen, Maria Lund |
author_facet |
Paulsen, Maria Lund |
author_sort |
Paulsen, Maria Lund |
title |
Pre-bloom dynamics of the Subpolar North Atlantic microbial food web |
title_short |
Pre-bloom dynamics of the Subpolar North Atlantic microbial food web |
title_full |
Pre-bloom dynamics of the Subpolar North Atlantic microbial food web |
title_fullStr |
Pre-bloom dynamics of the Subpolar North Atlantic microbial food web |
title_full_unstemmed |
Pre-bloom dynamics of the Subpolar North Atlantic microbial food web |
title_sort |
pre-bloom dynamics of the subpolar north atlantic microbial food web |
publisher |
The University of Bergen |
publishDate |
2013 |
url |
https://hdl.handle.net/1956/7536 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
https://hdl.handle.net/1956/7536 |
op_rights |
Copyright the author. All rights reserved |
_version_ |
1766127610611367936 |