| 1. |
- Hansen, Benni W., et al.
(författare)
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In situ and experimental evidence for effects of elevated pH on protistan and metazoan grazers
- 2019
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 41:3, s. 257-271
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Tidskriftsartikel (refereegranskat)abstract
- Plankton succession was studied in a hyper-eutrophic stratified estuary, Mariager Fjord, Denmark. Above the pycnocline (15 m) pH increased from 8.5 to 9.2 and the oxygen increased to super saturation after 5 d of sunny weather due to high primary production. The protistan grazers were dominated by heterotrophic dinoflagellates and mixotrophic and heterotrophic ciliates. Metazooplankton was dominated by meroplankton, rotifers and the copepod, Acartia tonsa, all with a relatively low biomass. Cirriped nauplii occupied the upper strata while polychaete larvae populated the whole water column. Bivalve larvae occurred occasionally above the pycnocline even at very high pH. In pH challenge experiments, the mixotrophic ciliate Mesodinium rubrum was the least pH tolerant species, followed by Strombidium spp., which did not cope well with seawater pH > 8.5. Some heterotrophic dinoflagellates were more tolerant with net growth at pH > 9. The predominant rotifer Synchaeta sp. tolerated up to pH 9.5 and the copepod survived pH 10 but stopped producing eggs at pH 9.5 with unaffected egg hatching success. The polychaete and cirriped larvae tolerated pH 9.5, but bivalve larvae showed decreased survival already at pH 8.5. In situ distribution patterns and pH challenge experiments suggest that pH indeed contribute to structuring zooplankton distribution.
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| 2. |
- Swalethorp, Rasmus, et al.
(författare)
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Microzooplankton distribution in the Amundsen Sea Polynya (Antarctica) during an extensive Phaeocystis antarctica bloom
- 2019
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Ingår i: Progress in Oceanography. - : Elsevier. - 0079-6611 .- 1873-4472. ; 170, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- In Antarctica, summer is a time of extreme environmental shifts resulting in large coastal phytoplankton blooms fueling the food web. Despite the importance of the microbial loop in remineralizing biomass from primary production, studies of how microzooplankton communities respond to such blooms in the Southern Ocean are rather scarce. Microzooplankton (ciliate and dinoflagellate) communities were investigated combining microscopy and 18S rRNA sequencing analyses in the Amundsen Sea Polynya during an extensive summer bloom of Phaeocystis antarctica. The succession of microzooplankton was further assessed during a 15-day induced bloom microcosm experiment. Dinoflagellates accounted for up to 59 % of the microzooplankton biomass in situ with Gymnodinium spp., Protoperidiwn spp. and Gyrodinium spp. constituting 89 % of the dinoflagellate biomass. Strobilidium spp., Strombidium spp. and tintinids represented 90 % of the ciliate biomass. Gymnodiniwn, Gyrodinium and tintinnids are known grazers of Phaeocystis, suggesting that this prymnesiophyte selected for the key microzooplankton taxa. Availability of other potential prey, such as diatoms, heterotrophic nanoflagellates and bacteria, also correlated to changes in microzooplankton community structure. Overall, both heterotrophy and mixotrophy appeared to be key trophic strategies of the dominant microzooplankton observed, suggesting that they influence carbon flow in the microbial food web through top-down control on the phytoplankton community.
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