Expert web

By placing a component of the marine environment under controlled conditions, mesocosms provide important links between field studies and laboratory experiments. Project Leader Dr Paolo Simonelli and scientific site coordinators Drs Elin Lindehoff, Jamileh Javidpour, Romain Pete, Stella Berger and Tatiana Tsagaraki explain how they are opening up access to these unique resources for European scientist

Future temperature and salinity do not exert selection pressure on cyst germination of a toxic phytoplankton species

Abstract Environmental conditions regulate the germination of phytoplankton resting stages. While some factors lead to synchronous germination, others stimulate germination of only a small fraction of the resting stages. This suggests that habitat filters may act on the germination level and thus affect selection of blooming strains. Benthic ?seed banks? of the toxic dinoflagellate Alexandrium ostenfeldii from the Baltic Sea are genetically and phenotypically diverse, indicating a high potential for adaptation by selection on standing genetic variation. Here, we experimentally tested the role of climate-related salinity and temperature as selection filters during germination and subsequent establishment of A. ostenfeldii strains. A representative resting cyst population was isolated from sediment samples, and germination and reciprocal transplantation experiments were carried out, including four treatments: Average present day germination conditions and three potential future conditions: high temperature, low salinity, and high temperature in combination with low salinity. We found that the final germination success of A. ostenfeldii resting cysts was unaffected by temperature and salinity in the range tested. A high germination success of more than 80% in all treatments indicates that strains are not selected by temperature and salinity during germination, but selection becomes more important shortly after germination, in the vegetative stage of the life cycle. Moreover, strains were not adapted to germination conditions. Instead, highly plastic responses occurred after transplantation and significantly higher growth rates were observed at higher temperature. High variability of strain-specific responses has probably masked the overall effect of the treatments, highlighting the importance of testing the effect of environmental factors on many strains. It is likely that A. ostenfeldii populations can persist in the future, because suitable strains, which are able to germinate and grow well at potential future climate conditions, are part of the highly diverse cyst population. OPEN RESEARCH BADGES This article has been awarded Open Data badge. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5061/dryad.c8c83nr. Learn more about the Open Practices badges from the Center for Open Science: https://osf.io/tvyxz/wiki.peerReviewe

Consistency in microbiomes in cultures of Alexandrium species isolated from brackish and marine waters

Phytoplankton and bacteria interactions have a significant role in aquatic ecosystem functioning. Associations can range from mutualistic to parasitic, shaping biogeochemical cycles and having a direct influence on phytoplankton growth. How variations in phenotype and sampling location, affect the phytoplankton microbiome is largely unknown. A high-resolution characterization of the bacterial community in cultures of the dinoflagellate Alexandrium was performed on strains isolated from different geographical locations and at varying anthropogenic impact levels. Microbiomes of Baltic Sea Alexandrium ostenfeldii isolates were dominated by Betaproteobacteria and were consistent over phenotypic and genotypic Alexandrium strain variation, resulting in identification of an A. ostenfeldii core microbiome. Comparisons with in situ bacterial communities showed that taxa found in this A. ostenfeldii core were specifically associated to dinoflagellate dynamics in the Baltic Sea. Microbiomes of Alexandrium tamarense and minutum, isolated from the Mediterranean Sea, differed from those of A. ostenfeldii in bacterial diversity and composition but displayed high consistency, and a core set of bacterial taxa was identified. This indicates that Alexandrium isolates with diverse phenotypes host predictable, species-specific, core microbiomes reflecting the abiotic conditions from which they were isolated. These findings enable in-depth studies of potential interactions occurring between Alexandrium and specific bacterial taxa

Effect of tertiary sewage effluent additions on Prymnesium parvum cell toxicity and stable isotope ratios

We investigated the ability of the ichthyotoxic haptophyte Prymnesium parvum to use sewage-originated nutrients applying stable carbon (C) and nitrogen (N) isotope techniques. P. parvum was cultured under N and phosphorus (P) sufficient and deficient conditions in either sewage effluent-based medium or in a nitrate- and phosphate-based control. Cell densities and toxicities were monitored and stable carbon N isotopes signatures (delta C-13 and delta N-15) of P. parvum and the sewage effluent analysed. Nitrogen and P sufficient cultures achieved the highest biomass followed by P and N deficient cultures, regardless of sewage effluent additions. The P deficient cultures with sewage effluent had higher toxicity, estimated as haemolytic activity (9.4 +/- 0 x 10(-5) mg Saponin equiv. cell(-1)) compared to the P deficient control and to all N deficient and NP sufficient cultures. Nutrient deficient conditions had no effect on the cell delta N-15, but a decreasing effect on delta C-13 in the inorganic N deficient treatment. Growth in sewage-based media was followed by a substantial increase in the cell delta N-15 (10.4-16.1.60) compared to the control treatments (2.4-4.9%o), showing that P. parvum is capable of direct use of sewage-originated N, inorganic as well as organic. Uptake of terrestrial derived C in the sewage treatments was confirmed by a decrease in cell delta C-13, implying that P. parvum is able to utilize organic nutrients in sewage effluent. (C) 2008 Elsevier B.V. All rights reserved

Minimizing economical losses with the help of “real-time” algal surveillance

Cyanobacterial blooms covering almost the entire Baltic Sea is a yearly feature during July-August. For the tourism industry at Öland island, SE Sweden, the economical losses during the summer 2005 amounted to 17-23 million euros. Remote sensing satellite images show that all the Öland beaches are covered with decomposing algae. In reality, these blooms rarely reach the western side of the island. To more accurately inform the public on the quality of the water for swimming, with the help of volunteers, a daily real-time surveillance of the algal densities on the beaches was performed. The volunteers (from 15 years old to pensioners) were trained at the Linnaeus University, from simple laboratory techniques, to more complicated ones such as identification and enumeration of the toxic cyanobacteria species. By latest 9.00 a.m., the public had access to information on the algal situation on 17 beaches. We could show that: 1) although remote sensing images showed Öland being surrounded by the blooms, our surveillance showed no algal accumulations on the beaches 2) that the real-time warning system boosted public confidence in the local water quality and during the first “Miss Algae”-summer 2006, the economical losses by the tourism industry turned in profits, the gain amounting to 17 million euros, 3) this kind of real-time surveillance is economical feasible due to low-costs involved, but also, the project has a great social value for the volunteers who mostly were pensioners. The volunteers who participated in “Miss Algae” had a good knowledge about the area they monitored (as their houses are located nearby) and could disseminate knowledge to the public in these areas. This kind of project also render a lot of interest regional, national and international, and can be used in advertising campaigns to increase tourism in the areas affected by algal blooms

Nitrogen uptake kinetics of Prymnesium parvum (Haptophyte)

The uptake rates of different nitrogen (N) forms (NO3−, urea, and the amino acids glycine and glutamic acid) by N-deficient, laboratory-grown cells of the mixotrophic haptophyte, Prymnesium parvum, were measured and the preference by the cells for the different forms determined. Cellular N uptake rates (ρcell, fmol N cell−1 h−1) were measured using 15N-labeled N substrates. P. parvum showed high preference for the tested amino acids, in particular glutamic acid, over urea and NO3− under the culture nutrient conditions. However, extrapolating these rates to Baltic Seawater summer conditions, P. parvum would be expected to show higher uptake rates of NO3− and the amino acids relative to urea because of the difference in average concentrations of these substrates. A high uptake rate of glutamic acid at low substrate concentrations suggests that this substrate is likely used through extracellular enzymes. Nitrate, urea and glycine, on the other hand, showed a non-saturating uptake over the tested substrate concentration (1–40 μM-N for NO3− and urea, 0.5–10 μM-N for glycine), indicating slower membrane-transport rates for these substrates

Data from: Future temperature and salinity do not exert selection pressure on cyst germination of a toxic phytoplankton species

Environmental conditions regulate the germination of phytoplankton resting stages. While some factors lead to synchronous germination, others stimulate germination of only a small fraction of the resting stages. This suggests that habitat filters may act on the germination level and thus affect selection of blooming strains. Benthic “seed banks” of the toxic dinoflagellate Alexandria ostenfeldii from the Baltic Sea are genetically and phenotypically diverse, indicating a high potential for adaptation by selection on standing genetic variation. Here, we experimentally tested the role of climate‐related salinity and temperature as selection filters during germination and subsequent establishment of A. ostenfeldii strains. A representative resting cyst population was isolated from sediment samples, and germination and reciprocal transplantation experiments were carried out, including four treatments: Average present day germination conditions and three potential future conditions: high temperature, low salinity, and high temperature in combination with low salinity. We found that the final germination success of A. ostenfeldii resting cysts was unaffected by temperature and salinity in the range tested. A high germination success of more than 80% in all treatments indicates that strains are not selected by temperature and salinity during germination, but selection becomes more important shortly after germination, in the vegetative stage of the life cycle. Moreover, strains were not adapted to germination conditions. Instead, highly plastic responses occurred after transplantation and significantly higher growth rates were observed at higher temperature. High variability of strain‐specific responses has probably masked the overall effect of the treatments, highlighting the importance of testing the effect of environmental factors on many strains. It is likely that A. ostenfeldii populations can persist in the future, because suitable strains, which are able to germinate and grow well at potential future climate conditions, are part of the highly diverse cyst population

Carbon isotope signature variability among cultured microalgae: Influence of species, nutrients and growth

In this study we have investigated whether the carbon isotopic signature differs between different groups and species of marine phytoplankton depending on growth phase, nutrient conditions and salinity. The 15 investigated algal species, representing the Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Dinophyceae and Haptophyceae classes were grown in batch monocultures and analysed for delta C-13 in both exponential and stationary phase. For all the cultured species, delta C-13 signatures ranged from -23.5 parts per thousand (Imantonia sp.) to - 12.3 parts per thousand (Nodulania spumigena) in the exponential phase and from - 18.8 parts per thousand (Amphidinium carterae) to - 8.0 parts per thousand (Anabaena lemmermannii) in the stationary phase. Three species (Dunaliella tertiolecta, Rhodomonas sp.. Heterocapsa triquetra) were also grown under nutrient sufficient and nitrogen or phosphorus deficient conditions. Nitrogen limitation resulted in a more negative delta C-13 signature, whereas no effect could be observed during phosphorus limitation compared to nutrient sufficient conditions. Growth of Prymnesium parvum in two different salinities resulted in a more negative delta C-13 signature in the 26 parts per thousand-media compared to growth in 7 parts per thousand-media. Our results show that the carbon isotopic signature of phytoplankton may be affected by salinity, differ among different phytoplankton species, between exponential and stationary phase, as well as between nutrient treatments. (C) 2009 Elsevier B.V. All rights reserved

Resource Partitioning Between Phytoplankton and Bacteria in the Coastal Baltic Sea

Eutrophication coupled to climate change disturbs the balance between competition and coexistence in microbial communities including the partitioning of organic and inorganic nutrients between phytoplankton and bacteria. Competition for inorganic nutrients has been regarded as one of the drivers affecting the productivity of the eutrophied coastal Baltic Sea. Yet, it is unknown at the molecular expression level how resources are competed for, by phytoplankton and bacteria, and what impact this competition has on the community composition. Here we use metatranscriptomics and amplicon sequencing and compare known metabolic pathways of both phytoplankton and bacteria co-occurring during a summer bloom in the archipelago of Åland in the Baltic Sea to examine phytoplankton bacteria resource partitioning. The expression of selected pathways of carbon (C), nitrogen (N), and phosphorus (P) metabolism varied over time, independently, for both phytoplankton and bacteria, indicating partitioning of the available organic and inorganic resources. This occurs regardless of eukaryotic plankton growth phase (exponential or stationary), based on expression data, and microbial community composition. Further, the availability of different nutrient resources affected the functional response by the bacteria, observed as minor compositional changes, at class level, in an otherwise taxonomically stable bacterial community. Resource partitioning and functional flexibility seem necessary in order to maintain phytoplankton-bacteria interactions at stable environmental conditions. More detailed knowledge of which organisms utilize certain nutrient species are important for more accurate projections of the fate of coastal waters

Boosting algal lipids: Diurnal shifts in temperature exceed the effects of nitrogen limitation

Algal lipids have been observed to increase during autumn conditions (low light, low mean temperature, and diurnal shift in temperature), in large‐scale outdoor photobioreactors. In this paper, we tested the effect of diurnal shifts in temperature (DS) and nitrogen (N) limitation on algal BODIPY lipid fluorescence cell−1 (BPF). We show that DS increased BPF in algal biomass up to 28% more compared with N limitation, the standard stressor to boost neutral lipids (NL) in commercial production. Biomass yield was constant, regardless the DS range (6°C‐12°C). A combination of both stressors had an additive effect on algal BPF. A polyculture from an outdoor photobioreactor was cultivated under controlled conditions at different regimes of light, temperature, and N limitation. DSs were mimicking autumn conditions with a difference of 6°C, 10°C, and 12°C between day and night. Biomass and BPF were monitored over one to two weeks, and NLs were stained with a fluorescent marker (BODIPY) and detected with flow cytometry. Results indicate that, during autumn conditions, daily heating and cooling processes in contrast to N limitation do not challenge the trade‐off between biomass production and BPF. During seasons when day temperature is still relatively high, DSs are rapid BPF boosting stressors, while N limitation could be applied to boost BPF further during other seasons