Abstracts 2023

Presently, three major challenges facing marine environments are warming, ocean acidification, and deoxygenation. To grasp the gravity and potential outcomes of these environmental shifts, it is crucial to establish a framework for understanding. Geological records offer invaluable perspectives in this regard. While these historical records cannot predict the future, they provide insights into the underlying processes and impacts. The field of palaeoceanography has a rich tradition of using species distribution data of various microorganisms to reconstruct past marine environments; a practice later complemented and partially replaced by advanced geochemical methods. Cutting-edge microanalytical techniques like LA-ICP-MS, ion probes, and synchrotron-based approaches such as μXRF have significantly enhanced analytical precision. For example, we can now examine calcite shell walls at a nanoscale level to understand elemental distribution. In this presentation, I will provide an overview of our synchrotron-based geochemical methods. Additionally, I will discuss how we integrate faunal analyses with morphometric μCT analyses. These combined techniques allow us to delve deeper into understanding past marine environmental changes.

¹Department of Geology, Lund University, Lund, Sweden

Swedish marine scientists are researching some of society’s most pressing challenges, however these efforts are hampered by limited access to research vessels, advanced equipment, expert technical support, and the required data. Sweden currently operates 6 large (>24m) research vessels, independently delivering research and data. This capacity should support all Swedish researchers to undertake research, and to deliver the data to the international community, however vessel access is limited and expensive, equipment is institutional, and the data is siloed and infrequently delivered to repositories in a coordinated way. The Swedish Research Council has approved development of the Swedish Research Vessel Infrastructure for Marine Research (SWERVE), which will align the research vessel infrastructures across government organisations to enhance access to vessels and equipment and deliver quality-controlled priority data to the international community. The infrastructure provided through the SWERVE project includes the Research Vessels Ocean Surveyor (SGU), Electra (SU), Oden (SPRS), KBV181 (Umeå), Svea (SLU), and Skagerak (GU), as well as the data infrastructure provided through the National Oceanographic Data Center (SMHI). Whilst SWERVE is yet to officially begin (with funding starting in 2024), a core deliverable will be to cover the cost of ship time for research voyages in 2025 and 2026. This will be open to any Swedish researcher (regardless of affiliation) and will be awarded through a competitive application process that will begin in 2024. It is imperative, therefore, that the research community start to plan now for their ship-time applications. This presentation will provide an overview of the project and provide some guidance on future applications for ship time.

¹University of Gothenburg
²Swedish University of Agricultural Sciences
³Stockholm University
⁴Swedish Polar Research Secretariat
⁵Swedish Geological Survey
⁶Umeå University
⁷Swedish Meteorological and Hydrological Institute

Seagrass meadows have been identified as one of the most important coastal habitats because of the multiple ecosystem services they provide. As a result, halting the rapid decline of seagrass meadows worldwide is considered a priority. Sexual reproduction has been recognized as a crucial process that supports genetic diversity and connectivity, both of which are key factors for the persistence of seagrass ecosystems. Yet, the mechanisms that drive flowering and thus sexual reproduction remain unclear, often hindering conservation efforts. To contribute to overcome this challenge, the aim of this study was to assess the relationship between environmental parameters that may influence sexual reproduction and patterns in genotypic richness in the widely distributed seagrass species Zostera marina (“eelgrass”). Two main approaches were employed: a localscale analysis of genetic diversity and connectivity in ten eelgrass meadows in the Kosterhavet archipelago on the Swedish west coast and a large-scale analysis of the environmental drivers of genotypic richness along the entire Northern hemisphere. Using 2bRAD sequencing to genotype 189 individuals, we found high levels of genotypic richness and genetic diversity in relation to previous assessments in a larger region of the west coast. Furthermore, this study revealed a sheltered-exposed pattern of genetic differentiation that follows a differential temperature gradient among the meadows assessed. By employing linear mixed-models and automatic model selection, we identified diffuse attenuation coefficient (a measure of light attenuation with depth used as an indicator of light availability), the interaction between diffuse attenuation coefficient and latitude and sea surface temperature as the most significant large-scale predictors of clonal richness in eelgrass meadows. Notably, a positive correlation between diffuse attenuation coefficient and genotypic richness indicates that clonality increases with decreasing light availability. The best model also suggests that the relationship between genotypic richness and diffuse attenuation coefficient tends to change from positive to negative as latitude increases, potentially leading to differing patterns of clonality in the northernmost locations. These findings highlight that incorporating both global and local factors in the design of seagrass conservation strategies might enable a better understanding of the drivers of genetic diversity, thereby facilitating more effective conservation efforts.

¹Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden

Marine-terminating glaciers are highly vulnerable to climate change due to warming from both atmospheric and seawater sources. Most tidal glaciers are rapidly retreating, but little is known on how glacier melting modifies coastal biogeochemical cycles. Here, we investigate carbon, alkalinity, and nutrient dynamics in an expanding proglacial tidal lagoon connected to Europe’s largest glacier in Iceland (Vatnajökull). N:P:Si ratios (2:1:30) showed a strong nitrogen limitation and a surplus of silica in the lagoon. Large natural variations in freshwater endmembers highlighted the complexity of determining sources. Dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and nitrogen were consumed in the lagoon (-110 to – 361, -18 to -34, and -2.1 to -2.7 mmol m^-2 lagoon area d^-1, respectively), while PO₄ was produced (0.8 to 0.9 mmol m^-2 d^-1). Floating chamber incubations revealed a CO₂ uptake of 26 ± 15 mmol m^-2 d^-1. Lagoon water near the glacier had a 170 % higher CO₂ uptake than near the ocean inlet likely driven by primary production stimulated by upwelling of nitrogen-rich waters. DIC and total alkalinity (TA) lateral export rates (outwelling) from the lagoon to the ocean, integrated over complete tidal cycles, were -2 and 23 mmol m^-2 d^-1 respectively. This implies net removal of TA from the ocean, lowering its buffer capacity against ocean acidification. The lagoon showed corrosive waters (all samples Ω_ar < 1) driven by glacial meltwater dilution of TA and CO₂ uptake. Overall, this thesis highlights how outwelling and estuarine transformations may modify the impact of glaciers on the coastal ocean. The complexity of the lagoons freshwater endmembers show the importance of a holistic view when investigating tidewater glacier systems.

¹Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden

The northern Baltic is undergoing a climate-driven transition, from a phytoplankton-based food web to one based on heterotrophic bacteria (1). Higher precipitation leads to increased riverine discharge of terrestrial organic matter, which shields phytoplankton from sunlight and provides food for bacteria (1-3). Recent studies have identified natural compounds which are useful for following land-sea-air exchange processes (4-6). Here we compare observations of marine bromoanisoles (BAs) and terrestrial DAME (drosophilin A methyl ether = 1,2,4,5-tetrachloro-3,6-dimethoxybenzene) (Figure 1) in streams and estuaries of Västerbotten County (VC, 2018-2021) (4) versus Lake Torneträsk (LT, Sept. 2022, 68o 22’N, 19o 06’E) and its tributaries in subarctic Sweden. Sampling and analytical methods are reported in (4). The ΣBAs (2,4-DiBA + 2,4,6-TriBA) and DAME in five VC streams averaged 108±32 pg/L and 307±161 pg/L respectively, while means for the ΣBAs and DAME in four VC estuaries were 554±302 pg/L and 201±102 pg/L (4). Higher abundance of DAME versus BAs in streams, and the reverse in estuaries, reflects in situ production of DAME in terrestrial and BAs in marine ecosystems. Identification of DAME in fungi and forest litter (5) is a further indication of a terrestrial source. Six streams entering LT showed lower levels: DAME 98±51 pg/L and ΣBAs 64±23 pg/L, while mean concentrations in the lake itself were DAME 88±7 pg/L and ΣBAs 48±8 pg/L. BAs and DAME are oversaturated in the estuaries and LT, with net volatilization to the atmosphere. Land-sea-air exchange can be summed up by “What goes around, comes around” (Figure 1). BAs and DAME volatilize from sea and land, disperse through the atmosphere, and return via precipitation and rivers (4).

Andersson, A. et al., 2015, Ambio 44, S345-S346. 2. Figueroa, D. et al., 2016, Microb. Ecol. 71, 789-801. 3.
Paczkowska, J. et al., 2020, Front. Mar. Sci. 7:80. 4. Bidleman, T. et al., 2023, Front. Mar. Sci. 10: 1161065. 5.
Bidleman, T. et al., 2023, Chemosphere, accepted. 6. Zhan, F. et al., 2023, Sci. Adv. 9, eadi8082.

¹Department of Chemistry, Umeå University (UmU), Umeå, Sweden
²Department of Ecology and Environmental Sciences, UmU, Umeå, Sweden
³Umeå Marine Science Centre, UmU, Hörnefors, Sweden
⁴Department of Marine Sciences, University of Connecticut Avery Point, Groton, CT, U.S.A.

A combined time-trend and trophic magnification study was carried out for ecologically relevant species of a Baltic Sea food web. Temporal trends (characterized by annual changes in %) were calculated for five species, including white-tailed sea eagle, common guillemot, harbor porpoise, eelpout, and blue mussel, whereas trophic magnification (characterized by trophic magnification factors, TMFs) was determined for the whole food web that contained the five aforementioned species as well as grey seal and herring. The study was carried out in a non-target screening (NTS) fashion, i.e. simultaneous determination of all possible chemical constituents of the sample, to detect and identify a wide variety of known and emerging chemical contaminants and assess their temporal trend (to track the contaminant levels and the effects of various regulations) and/or trophic magnification (to understand the exposure dynamics). An experimental and data processing NTS workflow was established and applied to the samples of this study. It consisted of four main parts: i) non-selective extraction of sample constituents, ii) clean-up from biogenic matrix components such as lipids, iii) gas chromatography–high-resolution mass spectrometry (GC–HRMS) data acquisition, and iv) a complementary highly-automated and fast NTS data processing workflow for data alignment, filtration/prioritization, and structure identification. The developed NTS workflow was applied to the sample set, revealing time-trend data for >600 identified and unknown compounds and trophic magnification data for >500 compounds in a given Baltic Sea food web. A number of emerging contaminants were reported for the first time in environmental biota samples as well as their annual change and TMF values. Nowadays, the legacy persistent organic pollutants show decreasing time trends, meaning the restrictions work. The data presented in this study can help assess the influence of the detected contaminants on the ecosystem.

¹Umeå University

Coastal environments in the Baltic Sea are influenced by climate change, including warming, oxygen depletion, and marine acidification, as well as emissions from industries such as pulp and paper mills, households, and agriculture. The effects of individual factors are more or less well studied, but there is limited knowledge about the consequences of interacting stressors, such as hydrographic processes like upwelling of cold, nutrient-rich, oxygen-poor water and marine heatwaves, in these already heavily impacted areas. Hanö Bay in the southwestern Baltic Sea is an ideal location to study this, as it has both coastal ecosystems and seafloor environments strongly affected by human activity and rapid hydrographic changes (eg. upwelling and marine heat waves). By combining traditional sampling with continuous monitoring of hydrographic conditions, we can capture short-term hydrographic processes that are challenging to capture through traditional monitoring programs. We will present results from continuous measurements carried out in Hanö Bay regarding currents, waves, water level, salinity, temperature, suspended particles, and oxygen.

¹Aanderaa-Xylem, Bergen, Norway
²Department of Geology, Lund University, Sweden
³Marint Centrum, Simrishamn, Sweden
⁴Department of Biology, Lund University, Sweden
⁵Hanö Torskrevsförening, Nogersund, Sweden

Phytoplankton respond rapidly to changing environmental conditions, influencing energy and carbon transfer to higher trophic levels, removal of carbon dioxide from the atmosphere and biogeochemical cycles. Phytoplankton are recognized as an important bioindicator of changing environmental conditions by different legislations, including the Marine Strategy Framework Directive. Ongoing monitoring programs which estimate primary production are logistically difficult, expensive, and time-consuming. Satellites also provide these estimates but are limited to the surface mixed ocean so can underestimate the contribution of deep chlorophyll maxima to primary production. We combined data collected at the BOOS BY5 station with sustained observations from an ocean glider for a full annual cycle in the Bornholm Basin. We showed that gliders can provide information at very small spatial and temporal scales across long periods. However, it needs to be supplemented by key in situ information such as phytoplankton biomass, community composition and photosynthetic yield parameters collected by the Swedish Monitoring Program to provide a deeper understanding of ecosystem functioning. These new estimates revealed a decoupling between Chl a, PB and PP was found in the southern Baltic Sea. Higher Chl a concentration was measured in early spring (March, 3.7 mg m^-3) when PP was lower, while this pattern was reversed in summer. This decoupling is explained by variability in the light-saturated maximum rates normalized to chlorophyll a concentration (PBmax) which correlated to phytoplankton size-structure. In summer, under stratified conditions, a Deep Chlorophyll Maximum (DCM) occurred (19.6 mg m^-3) and contributed disproportionately to the total annual production. Our project demonstrated that gliders could improve existing monitoring in the Baltic Sea by revealing features hidden to ships and satellite at the current resolution but require continued collection of in situ data.

¹Voice of the Ocean Foundation, Skeppet Ärans Väg 19, 42671 Västra Frölunda, Sweden
²Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden

Elemental composition of phytoplankton (C:N:P stoichiometry) is an important tool to assess the state of nutrient availability in an ecosystem. Environmental conditions can shape the stoichiometry of plankton biomass at large spatial scale (latitude), but our understanding of the variability of autotroph stoichiometry in relation to the dynamics of plankton microbial communities is incomplete. At the Linnaeus Microbial Observatory (LMO), an offshore monitoring station in the Western Gotland Basin, we found that the nano- and picoplankton communities are the main drivers of the stoichiometry across the year. The Baltic Sea is known for its North-South gradients of temperature, salinity and limiting nutrient. Combining results from sampling transects covering the spring and summer bloom conditions, we are exploring if the dominance of the nano- and picophytoplankton follows the salinity gradient and if it is persistent during the major production periods in the Baltic Sea.

¹Linnæus Center for Ecology & Evolution of Microbial Systems (EEMiS), Linnæus University, Sweden
²School of Business, Innovation & Sustainability, Halmstad University, Sweden

In recent decades, cyanobacterial blooms have increased in their magnitude, frequency and distribution in the Baltic Sea. Cyanobacteria have poorer nutritional quality than other phytoplankton taxa (e.g., diatoms) and are expected to have negative effects on pelagic food web efficiency (FWE) and quality, but these potential effects are yet to be verified. We conducted a 29 days mesocosm experiment to contrast the effects of cyanobacteria (Aphanizomenon sp.) and diatoms, combined with water mixing frequency (high vs low), on pelagic FWE and food web quality. The experiment consisted of four treatments with three replicates: diatoms with high mixing, diatoms with low mixing, cyanobacteria with high mixing and cyanobacteria with low mixing. At the end of the experiment, we found lower zooplankton production; primary production and FWE (i.e., the ratio between zooplankton production and sum of phytoplankton and bacterial production) in the cyanobacterial treatments. High mixing increased the FWE. Food web quality measured in terms of the ratio between ω3 and ω6 polyunsaturated fatty acids (ω3:ω6) in zooplankton was lower in the cyanobacterial treatments than in the diatom treatments. The nitrogen-fixing Aphanizomenon sp. induced a decrease in δ¹⁵N and δ¹³C isotopic signals of seston and zooplankton, indicating assimilation and trophic support of diazotrophic N in zooplankton in the cyanobacterial treatments. Overall, our results imply that climate change-induced increases in cyanobacterial blooms likely will lower pelagic FWE and food web quality in the Baltic Sea.

¹Department of Ecology and Environmental Science, Umeå University, 90187 Umeå, Sweden
²Umeå Marine Sciences Centre, Umeå University, 90571 Hörnefors, Sweden
³Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden
⁴Latvian Institute of Aquatic Ecology, Riga, Latvia
⁵Marine Research Institute, Klaipėda University, Klaipėda, Lithuania
⁶Center for Physical Sciences and Technology, Institute of Physics, Vilnius, Lithuania
⁷Department of Biology and Environmental Sciences, Centre for Ecology and Evolution in Microbial Model Systems – EEMiS, Linnaeus University, Kalmar SE-39182, Sweden
⁸Department of Ecoscience, Aarhus University, 4000 Roskilde, Denmark

Prokaryotic respiration constitutes approximately one-third of total respiration in marine ecosystems and is central to drive basic cellular processes. Maintenance respiration constitutes two-third of prokaryotic respiration and is particularly significant in cold and at oligotrophic conditions. Maintenance respiration drives activities suggested to sustain prokaryotic cell integrity, macromolecule repair and osmoregulation, not directly contributing to cell growth. However, processes that dominates maintenance activities in nature is unknown. Using a mesocosm experiment, we show that differential expression of specific metabolic genes is connected to conditions favoring high share of maintenance respiration, whereas no morphological features coupled to maintenance conditions could be demonstrated. However, a higher frequency of morphological features like cell-cell connections, membrane blebbing and release of membrane vesicles were coupled to higher growth rates. These morphological features were also supported by differential gene expression. The rod cell-shape dominated among marine prokaryotes at low productive conditions, while vibroids dominated at higher growth rates. Large scale gene patterns suggested maintenance activities to include osmoregulation, modification of translational machinery, increased ATP production and RNA processing. At the taxonomic level, most maintenance activities were driven by members of Gamma-Proteobacteria and Archaea. This motivates further study of prokaryotic morphological features during summer, while investigations of gene expression patterns during winter conditions can advance knowledge about prokaryotic maintenance activities.

¹Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
²Umeå Marine Sciences Centre, Norrbyn 557, SE-905 71 Hörnefors, Sweden
³Centre for Ecology and Evolution in Microbial Model Systems – EEMiS, Linnaeus University, SE-391 82 Kalmar, Sweden
⁴Umeå Core Facility for Electron Microscopy, Department of Chemistry, Umeå University, 901 87 Umeå, Sweden
⁵Department of Molecular Biology, Umeå University, Umeå, Sweden

Bacteria are major utilizers of dissolved organic matter in aquatic systems. In coastal areas bacteria are supplied with a mixture of food sources, spanning from refractory terrestrial dissolved organic matter to labile marine autochthonous organic matter. Climate scenarios indicate that in northern coastal areas, the inflow of terrestrial organic matter will increase, and autochthonous production will decrease, thus bacteria will experience a change in the food source composition. How bacteria will cope with such changes is not known. Here, we tested the ability of an isolated bacterium from the northern Baltic Sea coast, Pseudomonas sp., to adapt to varying substrates. We performed a 7-months chemostat experiment, where three different substrates were provided: glucose, representing labile autochthonous organic carbon, sodium benzoate representing refractory organic matter, and acetate – a labile but low energy food source. Growth rate has been pointed out as a key factor for fast adaptation, and since protozoan grazers speed-up the growth rate we added a ciliate to half of the incubations. The results show that the isolated Pseudomonas is adapted to utilize both labile and ring-structured refractive substrates. The growth rate was the highest on the benzoate substrate, and the production increased over time indicating that adaptation did occur. Further, our findings indicate that predation can cause Pseudomonas to change their phenotype to resist and promote survival in various carbon substrates. Genome sequencing reveals different mutations in the genome of adapted populations compared to the native populations, suggesting the adaptation of Pseudomonas sp. to changing environment.

¹Department of Ecology and Environmental Science, Umeå University, Sweden
²Umeå Marine Sciences Centre, Umeå University, Hörnefors

Eutrophication continues to be an environmental challenge in large parts of the Baltic Sea. However, the Gulf of Bothnia has to a large extent been considered more pristine and not affected by the eutrophication issues of the southern sea basins. The Gulf of Bothnia has lower levels of nutrient concentrations in comparison to the southern basins, and has historically been described as mainly phosphorous limited . However, in recent years there have been increasing nutrient levels and indications of a change towards nitrogen limitation in parts of the area. The aim of this study was to assess the changes in nutrient levels and limiting nutrient in different areas in the Gulf of Bothnia during the past 30 years, based on large datasets from the Swedish and Finnish monitoring programs. Results show that nitrogen limitation prevailed in the offshore Bothnian Sea all through the investigated 30-year period, in contrast to the previous general view of the basin being phosphorus limited. In the offshore Bothnian Bay, the inorganic nitrogen to phosphorus ratios showed decreasing trends during the past 20 years, but the basin is still distinctly phosphorus limited. The change from nitrogen limitation in the Bothnian Sea to phosphorus limitation in the Bothnian Bay occurs in the Northern Quark area with an abrupt shift at around 63.30 degrees N. Coastal areas in both the Bothnian Sea and the Bothnian Bay were found to be mainly phosphorus limited, but with an increasing tendency towards nitrogen limitation with decreasing latitude. The difference in limiting nutrient in combination with the actual nutrient levels have a large impact on the ecosystems in the two basins. The Bothnian Bay and the Bothnian Sea are distinctly different and should be managed as two separate waterbodies and not aggregated under the collective name of the Gulf of Bothnia.

¹Umeå Marine Sciences Center, Umeå university, Sweden
²Department of Ecology and Environmental Science, Umeå University, Sweden

The ecological conditions in the Baltic Sea are becoming increasingly volatile and unpredictable regarding species composition and population developments, and higher trophic-level organisms often exhibit negative trends in abundance and growth. Such perturbations motivate knowledge-building and management based on the ecosystem approach, where several trophic levels and external pressures are studied simultaneously. Here we study environmental transitions in the Baltic Sea by compiling and analysing environmental monitoring data collected by Sweden, HELCOM, and ICES. In one case study, we elucidate under which circumstances the riverine load of organic matter was related to a decline of the deposit-feeding of amphipod Monoporeia affinis in the Gulf of Bothnia. For Bothnian herring Clupea harengus, it is clear that the truncation of the size distribution of older age classes occurred as M. affinis disappeared. In case study two, smaller blue mussel sizes coincide with higher cyanobacteria production, thus drastically reducing the food basis for eider (Somateria mollissima). No other dominant seabird population that is not dependent on mussels has shown a similar decline; we hence suggest that changes in primary production have led to a decline in the eider population due to reduced blue mussel growth. The bottom-up approaches applied in the two case studies do not contradict top-down effects such as fishing and apex predatory pressure. However, the importance of bottom-up effects linked to primary producers needs improved consideration in management.

¹Swedish Institute for the Marine Environment (SIME), Gothenburg University
²RISE Research Institutes of Sweden, Department Agriculture and Food, Gothenburg

There is little doubt that climate change is occurring, but uncertainty remains regarding its magnitude and how biodiversity and ecosystem services will be affected, particularly in aquatic environments. The overarching aim with our broad project is to advance knowledge and understanding of how temperature change affects biodiversity and functioning of aquatic communities, to ultimately foresee how global warming will modify the Baltic Sea. To achieve this, we study a heated bay that has been influenced by 50 years of ‘experimental’ warming via thermal discharge from a nuclear power plant and compare findings with patterns in a nearby unheated control bay. Using this model system, we address the following three overarching questions: i) How do Baltic Sea communities alter and/or adapt after 50 years of warming; ii) How does 50 years of heating affect biochemical processes and greenhouse gas emissions; and iii) To what extent are the changes/adaptations due to climate change reversible if original conditions are restored? To address these questions, we combine realistic large-scale, long-term observational approaches with reciprocal translocation experiments in the field, and laboratory thermal incubation experiments. Both biological and chemical patterns and processes in the bottom sediment and the water column are studied, including spatiotemporal dynamics of community composition, bacterial degradation processes, and greenhouse gas (e.g., methane) emissions. The presentation will provide a ‘big picture’ of our past, ongoing, and future research. This includes showcasing some of the approaches used as well as examples of research findings, ranging from biogeochemistry and production of greenhouse gases, via shifts in microbial community composition, through to modifications of zooplankton phenology and life-history strategies.

¹Centre for Ecology and Evolution in Microbial Model Systems (EEMiS), Linnaeus University, Sweden
²Department of Biology and Environmental Sciences, Linnaeus University, Sweden

Microalgal solutions as bioremediation of waste provide a new efficient way of recovering nutrients and carbon dioxide (CO₂) from industrial waste streams, with the additional benefit of producing valuable biomass. In temperate regions there is an inevitable decrease in autotrophic production during September to March due to lack of light. Reduced production is followed by decreased capacity to capture CO₂ and nutrients. A mixotrophic microalgae is an autotroph, using the sun’s energy to bind CO₂ into biomass and at the same time a heterotroph, like an animal that uses organic carbon (C) sources. Mixotroph production will extend the cultivation season during winter conditions of low temperature and light, and increase recover efficiency on a yearly basis. When tested in pilot scale raceway ponds mixotrophic production increased biomass production three-fold using glucose and nine-fold using whey permeate as organic C source, compared to autotrophic production during November to March. Loss of algal biomass during night, due to respiration and cell mortality, can reduce 53% of the biomass synthesized in daylight. Mixotrophic cultivation can be used to counteract the negative effects as organic C provides energy for cell maintenance and division during darkness. When tested, mixotrophic production had a biomass gain of 20-40% during night while the autotrophic control lost 5-10% of the biomass. Mixotrophic cultivation has the potential to extend the cultivation season to the whole year and compensate 80-100% for nutrient uptake and 10-50% for CO₂ capture, compared to autotroph production during winter.

¹Centre of Ecology and Evolution and Microbial Model Systems, Department of Biology and Environmental Science, Linnaeus University, 39231 Kalmar, Sweden.
²School of Business, Innovation and Sustainability, Halmstad University 30118, Halmstad, Sweden.