| 1. |
- Andersson, Agneta, et al.
(author)
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Microbial food web changes induced by terrestrial organic matter and elevated temperature in the coastal northern Baltic Sea
- 2023
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In: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 10
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Journal article (peer-reviewed)abstract
- Climate change has been projected to cause increased temperature and amplified inflows of terrestrial organic matter to coastal areas in northern Europe. Consequently, changes at the base of the food web favoring heterotrophic bacteria over phytoplankton are expected, affecting the food web structure. We tested this hypothesis using an outdoor shallow mesocosm system in the northern Baltic Sea in early summer, where the effects of increased temperature (+ 3°C) and terrestrial matter inputs were studied following the system dynamics and conducting grazing experiments. Juvenile perch constituted the highest trophic level in the system, which exerted strong predation on the zooplankton community. Perch subsequently released the microbial food web from heavy grazing by mesozooplankton. Addition of terrestrial matter had a stronger effect on the microbial food web than the temperature increase, because terrestrial organic matter and accompanying nutrients promoted both heterotrophic bacterial production and phytoplankton primary production. Moreover, due to the shallow water column in the experiment, terrestrial matter addition did not reduce the light below the photosynthesis saturation level, and in these conditions, the net-autotrophy was strengthened by terrestrial matter enrichment. In combination with elevated temperature, the terrestrial matter addition effects were intensified, further shifting the size distribution of the microbial food web base from picoplankton to microphytoplankton. These changes up the food web led to increase in the biomass and proportion of large-sized ciliates (>60 µm) and rotifers. Despite the shifts in the microbial food web size structure, grazing experiments suggested that the pathway from picoplankton to nano- and microzooplankton constituted the major energy flow in all treatments. The study implies that the microbial food web compartments in shallow coastal waters will adjust to climate induced increased inputs of terrestrial matter and elevated temperature, and that the major energy path will flow from picoplankton to large-sized ciliates during the summer period.
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| 2. |
- Berglund, Åsa M. M., 1978-, et al.
(author)
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Effects on the food-web structure and bioaccumulation patterns of organic contaminants in a climate-altered Bothnian Sea mesocosms
- 2023
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In: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 10
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Journal article (peer-reviewed)abstract
- Climate change is expected to alter global temperature and precipitation patterns resulting in complex environmental impacts. The proposed higher precipitation in northern Scandinavia would increase runoff from land, hence increase the inflow of terrestrial dissolved organic matter (tDOM) in coastal regions. This could promote heterotrophic bacterial production and shift the food web structure, by favoring the microbial food web. The altered climate is also expected to affect transport and availability of organic micropollutants (MPs), with downstream effects on exposure and accumulation in biota. This study aimed to assess climate-induced changes in a Bothnian Sea food web structure as well as bioaccumulation patterns of MPs. We performed a mesocosms-study, focusing on aquatic food webs with fish as top predator. Alongside increased temperature, mesocosm treatments included tDOM and MP addition. The tDOM addition affected nutrient availability and boosted both phytoplankton and heterotrophic bacteria in our fairly shallow mesocosms. The increased tDOM further benefitted flagellates, ciliates and mesozooplankton, while the temperature increase and MP addition had minor effect on those organism groups. Temperature, on the other hand, had a negative impact on fish growth and survival, whereas tDOM and MP addition only had minor impact on fish. Moreover, there were indications that bioaccumulation of MPs in fish either increased with tDOM addition or decreased at higher temperatures. If there was an impact on bioaccumulation, moderately lipophilic MPs (log Kow 3.6 - 4.6) were generally affected by tDOM addition and more lipophilic MPs (log Kow 3.8 to 6.4) were generally affected by increased temperature. This study suggest that both increased temperatures and addition of tDOM likely will affect bioaccumulation patterns of MPs in shallow coastal regions, albeit with counteracting effects.
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| 3. |
- Blackburn, Nicholas, et al.
(author)
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The use of an automated organism tracking microscope in mesocosm experiments
- 2022
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In: Limnology and Oceanography. - : John Wiley & Sons. - 1541-5856. ; 20:12, s. 768-780
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Journal article (peer-reviewed)abstract
- A method for automatically counting and measuring sizes and motility behavior of zooplankton and phytoplankton in water samples is presented. Two video cameras are focused on separate optical chambers of different sizes. The chambers are filled and emptied repeatedly by synchronized pumps. Real-time motion analysis is performed by computer on the respective video feeds. Fluorescence from chlorophyll a (Chl a) is imaged at single pixel resolution. Measured parameters for individual organisms include size, swimming velocity, motility patterns, and chlorophyll fluorescence density. The system was tested during a mesocosm experiment where it was mounted on one of several mesocosm columns. The results were validated against Chl a measurements and microscopy counts. A sampling interval of 1 per day revealed detailed dynamics of chlorophyll activity as well as shifts in both the phytoplankton and zooplankton community structure over the course of a month. A helix coefficient, a metric related to organism motility behavior, showed substantial variation over time, consistent with changing plankton communities. Sampling rates as frequent as 1 per hour enables detailed analysis of diurnal vertical migration and similar phenomena at fixed sampling points.
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| 4. |
- Griniene, Evelina, et al.
(author)
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Lack of ciliate community integrity in transitional waters : A case study from the Baltic Sea
- 2019
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In: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 226
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Journal article (peer-reviewed)abstract
- The Baltic Sea, one of the world's largest brackish water environments, is particularly suitable for studies aiming to understand biodiversity in saltwater-freshwater mixing zones, i.e., transitional waters at different spatial and temporal scales. To evaluate diversity fluctuations in the pelagic microbial communities experiencing frequent brackish water intrusions, we analyzed seasonal dynamics of ciliates inhabiting transitional waters of the Curonian Lagoon. During the intrusion periods, the community presented a mixture of fresh- and brackish taxa, with no specific autochthonous component unique to the transitional waters. In the plume area, outside of the lagoon, we found that (i) high biodiversity was due to mixing of two distinct assemblages, and (ii) freshwater taxa are rather resistant to salinity change, their abundance decreases almost linearly with the increasing salinity, following conservative mixing model. Small unidentified Lohmanniella occurring exclusively in the plume zone during our survey possibly presents an autochthonous component based on locally available resource. Also mixed assemblage of the plume is characterised by absence of large predatory ciliate species.
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| 5. |
- Skrobonja, Aleksandra, et al.
(author)
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Multiple impacts of humic-rich dissolved organic carbon on methylmercury accumulation in heterotrophic pelagic food webs
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Other publication (other academic/artistic)abstract
- In this study we investigate how humic-rich dissolved organic carbon (DOC) impacts the bioaccumulation of methylmercury (MeHg) in coastal pelagic lower food webs. Mesocosm scale ecosystems with four levels of humic-rich DOC (ranging from 4 mg L-1 – no added DOC - up to 8.0 mg L-1) were run for 36 days and the bioaccumulation factor (BAF) of MeHg was determined in four seston size fractions at the end of the experiment. The pelagic food web was highly heterotrophic in all treatments with 72%−88% bacteria production of the total basal production. Increases in humic-rich DOC in coastal areas, manifested in our study as a shift towards more heterotrophic systems, can impact the bioaccumulation of MeHg through multiple processes. We found an increase in dissolved MeHg concentration with increased DOC loading, indicating a shift in partitioning from the particulate to the dissolved phase. However, a separate experiment showed that the presence of the humic-rich DOC lowered the bioavailability of dissolved MeHg with 40% across our study range, supporting previous results that the amount of MeHg incorporated at the base of the food web is not simply determined by the total concentration of dissolved MeHg. Our determined BAFs from the experiment supported this conclusion and we also calculated a corrected BAF’ value that took into account the change in MeHg bioavailability to isolate the impact on biomagnification processes. The range in MeHg log BAF’ values was 4.5−4.7 and 5.8−6.0 for 20-50 μm and >200 μm seston size fractions, respectively. Higher BAF’ values were observed in the highest DOC treatment and in our reference for some seston size classes. The high BAF’ at the highest DOC level may be explained by the large fraction of bacteria production observed for this treatment. The high BAF in the reference system could be explained by a slightly larger proportion of energy going through the autotrophic food web causing a higher trophic transfer efficiency of MeHg at the low trophic levels in the web. Taken together our results demonstrate a complex impact of humic DOC and pelagic food web heterotrophy on MeHg bioaccumulation in seston with partly counteracting processes. A detailed understanding of the factors controlling these multiple processes are important for accurate predictions of the net impact on MeHg bioaccumulation in coastal food webs following different environmental change scenarios.
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| 6. |
- Zilius, Mindaugas, et al.
(author)
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Spatiotemporal patterns of N2 fixation in coastal waters derived from rate measurements and remote sensing
- 2021
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 18, s. 1857-1871
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Journal article (peer-reviewed)abstract
- Coastal lagoons are important sites for nitrogen (N) removal via sediment burial and denitrification. Blooms of heterocystous cyanobacteria may diminish N retention as dinitrogen (N2) fixation offsets atmospheric losses via denitrification. We measured N2 fixation in the Curonian Lagoon, Europe's largest coastal lagoon, to better understand the factors controlling N2 fixation in the context of seasonal changes in phytoplankton community composition and external N inputs. Temporal patterns in N2 fixation were primarily determined by the abundance of heterocystous cyanobacteria, mainly Aphanizomenon flos-aquae, which became abundant after the decline in riverine nitrate inputs associated with snowmelt. Heterocystous cyanobacteria dominated the summer phytoplankton community resulting in strong correlations between chlorophyll a (Chl a) and N2 fixation. We used regression models relating N2 fixation to Chl a, along with remote-sensing-based estimates of Chl a to derive lagoon-scale estimates of N2 fixation. N2 fixation by pelagic cyanobacteria was found to be a significant component of the lagoon's N budget based on comparisons to previously derived fluxes associated with riverine inputs, sediment-water exchange, and losses via denitrification. To our knowledge, this is the first study to derive ecosystem-scale estimates of N2 fixation by combining remote sensing of Chl a with empirical models relating N2 fixation rates to Chl a.
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