Biology subjects

Spilling, K.

Publications and source records attributed to Spilling, K..

6 recordsLinked to original sources

bioRxiv2026

A low-cost method for collecting and measuring sinking speed of particles in coastal zones

Sinking marine particles is a key process regulating carbon export through the biological carbon pump, yet direct measurements of sinking dynamics remain limited in many coastal environments. One barrier is that most existing approaches require expensive instrumentation and large research platforms. Here, we present a low-cost, modular method for concentrating fast-sinking particles and measuring their individual sinking velocities under controlled conditions. This combines large settling tanks (110 L) for field-based particle fractionation with a video-based tracking system that quantifies the sinking behavior of natural marine particles. The particle sinking speed chamber is surrounded on three sides by a temperature-controlled water chamber, minimizing the problem of advection during measurements. The post-processing Python script delivers sinking velocity, particle size, circularity, and RGB-based properties for large numbers of particles. The method accuracy was validated using reference beads with known theoretical sinking velocities derived from Stokes law. Field deployments in the Baltic Sea demonstrated successful enrichment of fast-sinking particles and stable operation from both a research vessel and a small boat. Compared to existing methods, the approach substantially reduces logistical and financial barriers while maintaining particle-resolved measurements and compatibility with complementary biogeochemical analyses. This enables a broader observational coverage of sinking particle processes across environments that are currently underrepresented in carbon export studies.

biochemistry↗

bioRxiv2025

Biomass Production, Phosphorus Use Efficiency, and Fatty Acid Composition in Phaeodactylum tricornutum Cultivated in Wastewater from an Atlantic Salmon Recirculating Aquaculture System

Recirculating Aquaculture Systems (RAS) are becoming increasingly important as a sustainable method for fish production. However, further advancements are needed to enhance the sustainability of RAS, particularly in the management of waste-streams. Furthermore, the capital and operational expenditures of running a RAS is high, so solutions turning waste-streams into added value is a focus area for the industry moving forward. Wastewater is high in nitrogen, and phosphorus (P) is foreseen to be the limiting nutrient. Here we evaluated the growth dynamics, biomass production, nutrient uptake, phosphorus use efficiency (PUE), and fatty acid composition of the diatom Phaeodactylum tricornutum cultivated in aquaculture wastewater (AWW) from a land-based Atlantic salmon RAS. The diatom was cultivated in various treatments at pilot scale (10 L), including 100% AWW and AWW supplemented with silicon (Si) and P, and compared with a control treatment using Guillards F/2 medium. The highest dry weight biomass concentrations of [~]2.0 g L-{superscript 1} was achieved for the nutrient-supplemented AWW treatments, even outcompeting the control, demonstrating its viability as a growth medium when supplemented with Si and P. The control treatment achieved the highest specific growth rate of 0.422 d-{superscript 1}. The "Si+P addition" treatment achieved the highest PUE, indicating that co-supplementation strategies can enhance phosphorus utilization. However, fatty acid yields, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were lower in AWW-based treatments, likely due to micronutrient deficiencies or the effect of possible contaminants. Despite this, P. tricornutum cultivated in AWW offers a sustainable and possible cost-effective solution for producing biomass and valuable fatty acids.

plant biology↗

bioRxiv2024

Effects of excess phosphate on a coastal plankton community

Eutrophication in the Baltic Sea has caused an imbalance in the inorganic nitrogen (N) to phosphorus (P) ratio, leaving excess phosphate (PO4) after the phytoplankton spring bloom that terminates after N-depletion. Using monitoring data, we demonstrated that the PO4 concentration has continued to increase in the outermost Gulf of Finland during past decades. We further investigated the fate of such excess PO4 in a two-week mesocosm (1.2 m3) experiment. The starting concentration of PO4 was 0.66 {micro}M, and treatments included a non-treated control (control), nitrate addition (N-add; 3.6 {micro}M), glucose addition (C-add; 25 {micro}M) and combined nitrate and glucose addition (N+C-add). The addition of N both in N-add and N+C-add treatments stimulated nano- and microphytoplankton, while the picophytoplankton abundance increased only after N-depletion. Also, the copepod biomass was positively affected by the N-addition. N2-fixing cyanobacteria were present but in low abundance. Carbon addition did not enhance heterotrophic bacterial uptake of PO4 contrary to our expectations, nor did it affect the phyto- or zooplankton community composition. The PO4 concentration was reduced to [~]0.4 {micro}M in the control and C-add treatments and to 0.16 {micro}M in the two N-amended treatments, with an inorganic N:P uptake ratio of 6.7. These results underscore the role of picophytoplankton in reducing the excess PO4 pool after the spring bloom, a function traditionally ascribed to bloom-forming diazotrophic cyanobacteria in the Baltic Sea.

microbiology↗

bioRxiv2024

Microbial remineralization processes during post-spring-bloom excess phosphate in the northern Baltic Sea

In the northern Baltic, post-spring-bloom low dissolved inorganic nitrogen to phosphorus conditions, degradation of N-rich organic matter potentially supports the drawdown of excess phosphate. During a 17-day-long mesocosm experiment in the south-west Finnish archipelago, we examined nitrogen, phosphorus and carbon acquiring extracellular enzyme activities in three size fractions (<0.2 {micro}m, 0.2-3 {micro}m, and >3 {micro}m), bacterial abundance, production, community composition and its predicted metabolic functions. The mesocosms received different carbon and nitrogen amendments to test for the effect of inorganic nutrient stoichiometry on enzymatic degradation processes that ultimately determine the export potential of organic matter. Alkaline phosphatase activity occurred mainly in the dissolved form and likely contributed to the excess phosphate conditions. In the beginning of the experiment, peptidolytic and glycolytic enzymes were predicted to be produced by free-living bacteria identified within the classes Actinobacteria and Alphaproteobacteria, whereas the contribution of picocyanobacteria increased towards the end. Our results imply that heterotrophic bacteria lost the competition to picocyanobacteria due to the lack of suitable energy sources. The high hydrolytic rates in fractions <0.2 {micro}m and 0.2-3 {micro}m, found in this study, could potentially retain inorganic nutrients in the surface layer and suppress downward fluxes of organic matter and hence carbon sequestration.

microbiology↗

bioRxiv2019

Impacts of reduced inorganic N:P ratio on three distinct plankton communities in the Humboldt upwelling system

The ratio of inorganic nitrogen to phosphorus (NP) is projected to decrease in the Eastern Boundary Upwelling Systems (EBUS) due to warming of the surface waters. In an enclosure experiment, we employed two levels of NP ratios (10 and 5) for three distinct plankton communities collected along the coast of central Chile (33{degrees}S). The primary effect of the NP treatment was related to different concentrations of NO3, which directly influenced the biomass of phytoplankton. Additionally, low inorganic NP ratio reduced the seston NP and Chl a-C ratios, and there were some effects on the plankton community composition, e.g. benefitting Synechococcus spp in some communities. One of the communities was clearly top down controlled and trophic transfer to grazers was up to 5.8% during the 12 day experiment. Overall, the initial plankton community composition was more important for seston stoichiometry and trophic transfer than the inorganic NP ratio. Any long term change in the plankton community structure will likely have greater impact than direct effects of a decreasing inorganic NP ratio on the Humboldt Current ecosystem.

plant biology↗

bioRxiv2019

Bacterioplankton dynamics driven by inter-annual variation in phytoplankton spring bloom communities in the Baltic Sea

In the Baltic Sea, climate change has caused shifts in the phytoplankton spring bloom communities with co-occurrence of diatoms and dinoflagellates. Such changes likely affect the composition and function of associated bacterioplankton, key members of the carbon cycling, although the actual effects are unknown. To understand how changes in phytoplankton impact on bacterioplankton composition and function, we analysed bacterioplankton communities and their production during different phases of the spring bloom in four consecutive years across the Baltic Sea, and related them to environmental variables. Phytoplankton communities varied largely in composition, modifying the taxonomic structure and richness of the associated bacterioplankton assemblages. In presence of certain diatoms (Achnanthes taeniata, Skeletonema costatum and Chaetoceros spp.), bacterial production and diversity were high and with more relative abundance of Flavobacteriia, Gammaproteobacteria and Betaproteobacteria. This bacterial community structure correlated positively with high diatom biomass and with high bacterial production rates. In contrast, during dinoflagellate-dominated blooms or when the diatom Thalassiosira baltica was abundant, both bacterial production rates and diversity were low, with bacterial communities dominated by SAR11 and Rhodobacteraceae. Our results demonstrate that, changes in the phytoplankton spring bloom will have profound consequences on bacterial community structure and their role in carbon cycling.

microbiology↗