A consequence of eutrophication in the Baltic Sea is growth of algae that accumulates in the coastal areas and beaches. Dense algal mats may cause anoxia or hypoxia and greatly reduce the recreational value of the area. Algae also functions as hyper accumulators of heavy metals and their metal levels may become toxic to higher trophic levels. The project Wetlands, Algae and Biogas (WAB) aims at removing algal beach cast for commercial use in biogas production and further use of the fermentation residues as fertilizer. Collection of algae would remove both nutrients and heavy metals from the Baltic Sea but leave us with large amounts of algae containing heavy metals. A concern for the biogas production based on these Baltic algae is the effects from the heavy metals, during fermentation, in the residues and the use of them as fertilizer. A literature review shows that the levels of heavy metals should not inhibit the biogas production but during the fermentation there is a loss of (48%) biological material and the metals are concentrated in the residues. Samples of algae from Trelleborg (SE) show higher concentrations of cadmium (Cd) than algae from Poland (PL). The Swedish residues border or surpass the legislative amount of heavy metals that are allowed to be applied to arable land in Sweden. This is both due to the higher concentrations of heavy metals and the differences between European and Swedish legislation. To use the residues as fertilizer detoxification is required, mainly for Cd in Sweden. There are effective methods, chemicals and ion exchangers (70-80%), for removing heavy metals from organic leachate. But these methods lack testing on a large scale, the costs and the environmental aspect of these methods on tons of algae per year are unknown. Co-fermentation with a suitable substrate would dilute the heavy metal concentration and could reduce possible problems such as hydrogen sulfide accumulation in the biogas. Another possible pathway for dealing with the heavy metal rich residues is as fertilizer for non-food crops such as the biofuel species willow (Salix). Willow is a fast growing tree that is a known accumulator of heavy metals and can be used as a remediation for contaminated soil. Based on the metal concentrations and respective legislation, estimations of 20 000 ha of willow for Trelleborg and 400 ha for Sopot beach (PL) is needed to process harvested algae. / Wetlands, Algae and Biogas (WAB)

The European eel is critically endangered (IUCN 2021), only 1% of the population remains and the recruitment has been estimated to be 5-10% of their historical values. The eel is in dire need of remedial efforts and many studies suggest that these efforts are best applied to elvers when these have ended their migration. To satisfy the need for suitable habitats of elvers, we need to understand which habitat is best suited to increase survival and growth. This study focuses on how habitat use of elvers, specifically use of gravel and sand bottom substrates, influences behaviour and activity. In a laboratory experiment, eels in aquaria with gravel substrate were 33 % less visible and had 50 % lower levels of observed activity than eels in aquaria with sand substrate. This difference in visibility and activity has implications for survival by affecting the ability to avoiding visual predators. If we can increase the chances of survival of elvers by strategical placement of gravel substrate as a remedial measure, we could be adding to the recovery of the population. / Europeisk ål är kritiskt hotad (IUCN 2021), endast 1% kvarstår av populationen och rekryteringen antas ligga runt 5–10% av historiska värden. Ålen är i stort behov av åtgärdsinsatser och många studier antyder att det är vid juvenil ålder då ålen avslutat sin vandring som insatser bäst kan tillämpas. För att tillgodose juvenila ålars behov av lämpligt habitat behöver vi kartlägga vilken typ av habitat som är bäst lämpad för överlevnad och tillväxt. Vid restaurering av vattendrag är det en relativt enkel insats att strategiskt placera substrat som förstärker ålens överlevnad. Denna studie har därför undersökt hur ålars habitatanvändning (grus- vs. sandsubstrat) påverkar beteende och aktivitet i ett laboratorieexperiment. De ålar som befann sig i akvarier med grussubstrat var 33 % mindre synlighet och observerades ha 50 % lägre aktivitet än de som befann sig i akvarier med sand. Dessa skillnader i synlighet och aktivitet kan ha en inverkan på överlevnadschanserna genom att det påverkar sannolikheten att kunna undvika visuella predatorer. Om vi kan öka chansen till överlevnad i juvenil ålder genom strategisk placering av grussubstrat vid åtgärdsinsatser bör detta bidra till att stärka populationen.

Flodpärlmusslan (Margaritifiera margaritifiera) är en stormussla och en effektiv filtrerare som skapar en viktig ekosystemtjänst i vattendraget. Flodpärlmusslan räknas som starkt hotad och är skyddad enligt direktiv och förordningar i Sverige. De största hoten mot arten är bland annat hög turbiditet, åkermark, kalhyggen samt brist på ekologiska kantzoner kring bestånden. Syftet med denna studie var att ta reda på vilka av nämnda hot som kan ha påverkat artens föryngring i tio utvalda vattendrag. Syftet var dessutom att ta reda på om hög turbiditet, åkermark och kalhygge påverkar föryngringen av arten i kombination med varandra vid användning av indexuträkningar och statistiska tester. Resultatet visade att medelvärdena för ett kombinerat indexresultat hadeen signifikant skillnad i kantzonerna. Detta kan innebär att hög turbiditet i kombination med höga andelar åkermark och kalhyggen har signifikant negativ påverkan på flodpärlmusslornas föryngring, främst i beståndens närområden. En övergripande analys gjordes också av varje enskilt vattendrag i studien som inkluderade markavvattning, vandringshinder samt brist på värdfisk, vilket också anses vara hot mot arten. Den övergripande analysen visade att samtliga vattendrag hade ett medelvärde av turbiditet som översteg det rekommenderade gränsvärdet.Flertalet vattendrag hade också blivit utsatta för markavvattning i åkermark och kalhygge medan andra hade brist på lövskog samt höga andelar åkermark och kalhygge i kantzonerna och delavrinningsområdena. Många vattendrag hade dessutom brist på värdfisk samt förekomst av vandringshinder uppströms från populationerna. Alla dessa faktorer kan ha haft stor påverkan på varför samtliga vattendrag i studien inte hade någon livskraftig föryngring, vilket överensstämmer med tidigare studier. / The freshwater pearl mussel (Margaritifera margaritifera) is an aquatic bivalve mollusc and an effective water filterer that establishes important ecosystem services in the streams. The species is considered endangered and is protected by several directives and regulations in Sweden. Some of the most substantial threats against the species are high turbidity, lack of ecological buffer zones in areas close to the populations, along with agricultural land and areas with high deforestation. The aim of the study was to investigate which of these threats affects the reproduction of the species in ten chosen streams. The aim of the study was also to investigate if high turbidity, agricultural lands and deforestation affect the reproduction in combination with each other. Results concluded that the aforementioned combination had a significantly negative effect on the reproduction of the species in the buffer zones when performing index calculations and statistical tests. An overall analysis of each specific water stream was also conducted that included artificial drainage of water, lack of host fish and migration barriers, all additional threats to the freshwater pearl mussel. The overall analysis concluded that all water streams in the study had higher average turbidity than the recommended limit. Some streams had also been affected by artificial water drainage, while other streams had a higher proportion of deforestations or a lack of ecological buffer zones and host fish. All these factors can have an impact on the lack of viable reproduction in each stream, corresponding to earlier studies.

Invasive alien species are the second biggest threat to global biodiversity. Biodiversity loss results in loss of ecosystem functions and resilience. Freshwater ecosystems are more sensitive to invasions; therefore, their biodiversity is decreasing at a much faster rate in comparison to terrestrial ones. This thesis focuses on one of three invasive alien aquatic plants present in Sweden: Nymphoides peltata, a sediment-rooted, floating-leaved plant originating from middle Europe and Asia. Since the early 1980’s N. peltata has been present in Lake Galten, the most western part of Mälaren. The current eradication work is carried out by light depletion through floating frames that shade the N. peltata colony. The aim of this work was to evaluate the efficiency of this method by assessing eventual recolonization of N. peltata in eradicated sites and suggesting possible improvements. Information and data were collected by reviewing existing literature on invasive species eradication as well as conducting interviews with experts followed by field observations in Munkhammar bay of Lake Galten. The choice of floating frames as the main eradication method has been proven valid since it counters N. peltata clonal growth and fragmentation capacity. Despite a reduction by 1.7% of total N. peltata coverage from 2019 to 2020, correlated with the increase in frame coverage, field observations showed that recolonization is happening. Suggested improvements are the use of frames as spreading barrier, to reduce clonal growth and fragmentation of large colonies, together with introducing a free-floating fiber sheet to properly seal the gap between shoreline and frames. A proactive covering of vulnerable shores with fiber sheet is also recommended. However, the lack of a coordinated national action plan and laws’ inadequacy weakens the possibility of a successful eradication. Tempestive adjustments of current legislations are needed since climate change will allow N. peltata to spread further north and produce viable seeds.

With the contribution of intraspecific trait variation (ITV) to ecological processes being increasingly appreciated, its role in defining niche characteristics arises as a topic of interest. I hypothesised that species with a high magnitude of ITV would occupy a larger climate niche breadth than species with little ITV. Trait and occurrence data for 211 angiosperm tree species across Puerto Rico was used to investigate this hypothesis. Multiple indices for climate niche breadth (NB) and intraspecific variation were calculated, after which regression tests were performed to identify and characterise any relationships between NB and ITV. I found consistent positive correlations between niche breadth and intraspecific variation values (a single negative result was present), supporting the hypothesis that ITV of functional traits has a positive influence on climate niche breadth. These results highlight the contribution of ITV to species distribution, though the mechanisms behind this relationship are unclear and present a question for future study.

Det är väl känt att urbaniseringen av våra landskap har minskat den biologiska mångfalden och bidragit till utrotningen av flertalet arter som inte kunnat anpassa sig till den nya miljön. För de arter som lyckats överleva i staden så finns det forskning som talar för att urbaniseringen nu driver deras evolution inom loppet av några få generationer. I den här uppsatsen undersöker jag tre aspekter av stadsmiljön som driver evolutionen hos vilda djur och växter: (1) habitatfragmenteringen, (2) den urbana värmeön och (3) föroreningar. Mitt syfte är att belysa detta fenomen, visa vidden av det, samt åskådliggöra hur urban evolution kan påvisas experimentellt genom att fördjupa mig i ett antal studier.   Forskningen visar att den urbana miljön påverkar evolutionen av en mångfald av arter från samtliga trofiska nivåer, både i form av anpassningar och genom stokastiska händelser. En studie visar hur stadens habitatfragmentering leder till minskad genetisk variation hos urbana populationer och hur genetisk drift tillsammans med minskat genflöde resulterar i genetiskt skilda urban och lantliga populationer. Andra studier påvisar anpassningar till stadens föroreningar och lokala klimat, vilket leder till genetisk divergens mellan urbana och lantliga populationer. En annan studie visar hur mutationer som induceras genom föroreningar resulterar i en ökad mutationshastighet hos populationer nära industrier. Utifrån de undersökta studierna så diskuteras hur de genetiska förändringarna orsakade av stadsmiljön får populationsdynamiska konsekvenser. Ett flertal arter har lyckats anpassa sig till den extrema urbana miljön och en diskussion förs om huruvida det kan införliva hopp om evolutionär räddning från de massutrotningar vi ser idag som följd av de mänskliga miljöförändringarna. Till sist utreds om och hur kunskapen om urban evolution kan användas för att utforma städer med grön infrastruktur som gynnar den biologiska mångfalden.

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A decline in the density of zoobenthos has taken place in Lake Abiskojaure in the northern Swedish mountains between 1988 and 2019 but no response can be seen in the abundance (CPUE) of Arctic charr (Salvelinus alpinus) that feed mainly on benthic invertebrates. To evaluate if possible shifts in resource use of charr explain this lack of change in population abundance, stomach contents (i.e. diet) of charr between 1985 and 2020 were analyzed. Charr diets changed during the study period, with decreasing contributions to the diet of larger sized prey and increasing contribution of smaller sized prey and zooplankton. A corresponding recent decline in charr growth, size, and condition factor was observed. The proportion of large prey in diets and charr growth both show a hump-shaped relationship with time before the recent decline, indicating consumption of large prey had a positive effect on charr growth. Densities of zooplankton in the lake did not change with time, meaning increases in diet proportions are driven by something else. Declines in nitrogen and phosphorous over time may have contributed to the decline in zoobenthos densities through nutrient limitation of primary production. The results from this study suggest charr has changed diet towards smaller, less energetically efficient prey as a response to declining zoobenthos levels, and that this has had a negative effect on charr growth, size, and condition factor. Additional declines in nutrients and zoobenthos abundance may further worsen charr performance and eventually be manifested as declining charr abundance.

Forests provide humans with a range of valuable ecosystem services, but current forest management practices may increase susceptibility to damage from disturbances such as pest insects. One such practise is the harvesting of residue, which decreases the amount of dead wood in the forest. Dead wood has been shown to be of importance for biodiversity and could decrease vulnerability to biotic disturbances. Sustainable forest management and conservation of biological diversity is required to maintain ecologically healthy forests. I aimed to investigate if biodiversity connected to dead wood could contribute to insect pest mitigation. I sampled ground-dwelling arthropods with pitfall traps in monoculture pine stands in Central Sweden on plots where dead wood had been either added or removed. To relate catches from pitfall traps to predation pressure of pest insects, I used plasticine model larvae to measure the attack rate. Contrary to my expectations, total arthropod abundance was higher when dead wood had been removed. Furthermore, the presence of dead wood had no effect on total arthropod diversity and diversity and abundance of predators. There was no relationship between predator catches and attack rates on plasticine model larvae. My results contradict previous findings that dead wood promotes biodiversity and pest mitigation. This highlights the need for studies targeting the more specific effects of different types of dead wood, in different types of forest stands on specific taxonomic groups and ecological processes, as results do not appear to be uniform across studies.

Gonyostomum semen is a raphidophyte microalgae that can be found in brown water lakes all over Sweden. The species forms substantial summer blooms that can completely dominate the phytoplankton community, largely due to its limited grazing pressure. To test whether parasites control the abundance of G. semen, as well as to study a newly discovered predator – prey interaction, three experiments were set up. The first experiment aimed to look at potential parasite interactions by screening for infections in natural environments, but none could be found. The second experiment built on the first by testing if the lack of parasites was due to physiological characteristics of G. semen, by exposing the species to diatom parasites and observing the cell’s response. The third experiment investigated the impact of a predatory ciliate on G. semen cell abundance. This predator – prey interaction was first observed in fresh lake water samples and had so far not been described in the literature. First, G. semen alone was exposed to the ciliate, and later the prey preference of the ciliate was examined by offering it four different potential prey species. The results from the first and second experiment suggested that G. semen does not have any parasites, potentially due to lack of a supportive cell wall. When interacting with parasite zoospores, the G. semen cells burst open, meaning that a successful infection would not be possible. The third experiment showed that the ciliate does feed on G. semen, and that it likely prefers G. semen over other types of prey. The limited top – down control on G. semen gives the species an ecological advantage and is seemingly one of the main reasons for G. semen’s success in spreading to new habitats.