Exploring Multiple Aspects of Taxonomic and Functional Diversity in Microphytobenthic Communities : Effects of Environmental Gradients and Temporal Changes

Biodiversity has traditionally been quantified using taxonomic information but the importance of also considering its functional characteristics has recently gained an increasing attention among microorganisms. However, studies exploring multiple aspects of taxonomic and functional diversity and their temporal variations are scarce for diatoms, which is one of the most important microbial groups in aquatic ecosystems. Here, our aim was to examine the taxonomic and functional alpha and beta diversities of diatoms in a coastal rock pool system characterized by a naturally high environmental heterogeneity. We also investigated the temporal differences in the diversity patterns and drivers. The relationship between the species richness and functional dispersion was temporally coherent, such that species-poor communities tended to be functionally clustered. The trend between the species richness and taxonomic uniqueness of community composition was temporally inconsistent, changing from negative to non-significant over time. Conductivity or distance to the sea or both were key determinants of species richness, functional dispersion, and uniqueness of community composition. The increase of community dissimilarity with an increasing environmental distance was stronger for the taxonomic than the functional composition. Our results suggest that even minor decreases in the species richness may result in a lowered functional diversity and decreased ecosystem functioning. Species-poor ecosystems may, however, have unique species compositions and high contributions to regional biodiversity. Despite changing the species compositions along the environmental gradients, communities may remain to have a high functional similarity and robustness in the face of environmental changes. Our results highlight the advantage of considering multiple biodiversity metrics and incorporating a temporal component for a deeper understanding of the effects of environmental changes on microbial biodiversity.Peer reviewe

Distribution patterns of epilithic diatoms along climatic, spatial and physicochemical variables in the Baltic Sea

The species richness and community composition of the diatom communities were studied in the Baltic Sea, Northern Europe, to enhance knowledge about the diversity of these organisms in a brackish water ecosystem. Many organisms in the Baltic Sea have been studied extensively, but studies investigating littoral diatoms are scarce. The goal of this study was to examine the importance of climatic, spatial and water physicochemical variables as drivers of epilithic diatoms in the Gulf of Finland and the Gulf of Bothnia. The variation in species richness was best explained by pH, total phosphorus and total nitrogen. Redundancy Analysis indicated that the most important factors correlating with species composition were air temperature, silicon, total phosphorus, water temperature, salinity and pH. Variation Partitioning showed that the species composition was mostly affected by climatic and spatial variables, whereas physicochemical variables had little impact. However, the strongest factor was the combined influence of climatic, spatial and physicochemical variables. The results suggest that diatom species richness in the northern Baltic Sea is primarily regulated by local factors, while climatic and spatial variables have little impact on richness. Species composition is mostly affected by climatic and spatial variables. We conclude that understanding the distribution patterns of Baltic Sea diatoms requires the inclusion of climatic, spatial and water chemistry variables.Peer reviewe

Threshold effects of climate change on benthic diatom communities: Evaluating impacts of salinity and wind disturbance on functional traits and benthic biomass

The responses of biotic communities and ecosystems to climate change may be abrupt and non-linear. Thus, resolving ecological threshold mechanisms is crucial for understanding the consequences of climate change and for improving environmental management. Here, we present a study on the threshold responses of benthic diatom communities that are an important component of all aquatic environments and strongly contribute to global primary production. We reach beyond the taxonomic perspective by focusing on the diversity and functions of diatom communities and benthic biomass along gradients of salinity and wind disturbance, whose climate-change-induced changes have been predicted to strongly affect biotic communities in the marine and brackish systems in the future. To improve the generality of our results, we examine three self-collected datasets from different spatial scales (6-830 km) and ecosystem types. We collected samples from rock pools or from littoral stones and studied taxonomic thresholds using Threshold Indicator Taxa Analysis (TITAN2). We investigated threshold responses of community diversity, community functions, and benthic biomass using t-tests and regression analyses. Our results indicated that decreasing salinity may result in increasing diver-sity but decreasing biomass of brackish communities, while the effects of increasing wind disturbance were contradictory among spatial scales. Benthic biomass correlated with the taxonomic and functional diversity, as well as with the body size distribution of communities, highlighting the importance of considering community functions and organismal size when predicting ecosystem functions. The most pronounced effects of decreasing salinity and increasing wind distur-bance on community functions were changes in the abundance of low-profile diatom species, which, due to the high resilience of low-profile diatoms, may lead to changes in ecosystem functioning and resilience. To conclude, decreasing salinity and increasing wind disturbance may lead to threshold responses of biotic communities, and these changes may have profound effects on ecosystem functioning along marine coastal areas.Peer reviewe

Exploring the diversity patterns of benthic diatoms along environmental, spatial and temporal gradients in the Baltic Sea

During the ongoing rapid environmental change, different aspects of biodiversity and its effects on ecosystem functioning need to be resolved. A lot has already been learned regarding the value of biodiversity, but due to the complexity of natural environments many aspects are still unresolved, especially about the patterns and effects of microorganismal diversity in marine and brackish environments. This is surprising, given that microorganisms play key roles in many ecosystem functions and the marine microorganisms are estimated to, e.g., provide the majority of Earth’s oxygen. To facilitate better understanding, studies conducted along large gradients and considering the functional diversity of communities can be useful. Large gradients provide insights into the variation of ecological patterns relative to the environment and can indicate the consequences of environmental change on community responses, and the functional diversity may describe the community characteristics and diversity-ecosystem functioning relationships more effectively than taxonomic diversity and allow the generalizations of results between organisms and ecosystems to be made. In this thesis, biodiversity patterns of benthic diatoms, a highly diverse and productive microorganismal group in all aquatic systems, were resolved along different environmental, spatial and temporal gradients in the coastal ecosystems of the Baltic Sea. Being one of the world’s largest brackish water ecosystems with a naturally strong gradient of salinity and climate and with a unique mixture of marine and freshwater species, the Baltic Sea provides an ideal platform for biodiversity research. Biodiversity patterns resolved here included analyzing the effects of benthic diatom diversity on ecosystem productivity, investigating spatial and temporal beta diversity patterns, i.e. the change in community composition between sites or sampling occasions, and examining the effects of environment on the distribution and diversity of diatoms. All studies were conducted as field studies to increase knowledge on real-world processes. The results revealed some significant new insights and showed that the diversity, especially functional diversity, of benthic diatoms may set the lower boundary for ecosystem productivity. Thus, productivity could be high even when the diatom diversity was low, but high diatom diversity seemed to consistently support high productivity. This positive relationship may be due to several reasons, such as more complete resource use or the facilitative effect in diverse communities, or complex ecological interactions. However, the diversity of diatoms varied substantially among different habitats, highlighting the need to consider environmental heterogeneity and large environmental gradients in biodiversity research. Spatial beta diversity studies conducted at different spatial scales indicated a general pattern: across steep environmental gradients, the taxonomic beta diversity was consistently high while the functional beta diversity remained considerably lower. This suggests that the ecosystem requirements for the functional characteristics of microphytobenthic organisms are highly similar in different environments, and that diatoms are able to meet these requirements in variable environments, which may indicate an insurance effect against environmental change. However, simulated species loss of communities significantly increased the functional beta diversity, suggesting that the deterioration of diversity may decrease resilience, and thus emphasizing the importance of biodiversity for the stable functioning of benthic ecosystems. Despite some similarities in the environmental drivers of diatom communities in different environments, environmental variables controlling the communities varied between and within gradients. Thus, the effect of environment on communities seems to be context-dependent and variable between regions, which emphasizes the need for large-gradient studies and the consideration of region-specific differences in, e.g., environmental management and conservation efforts. The seasonal and inter-annual variation in the composition and diversity of communities was investigated along a temporal gradient of two years. The taxonomic and functional composition of communities changed significantly between seasons and years, while diversity remained fairly stable. This refers to either an ample seed bank, i.e. locally occurring resting stages of species, or a large regional species pool and effective dispersal of species, which rescue the populations. However, diversity decreased during an exceptionally warm winter with a short ice-cover duration, which may suggest that climate warming affects the diversity of benthic communities. To conclude, this thesis has increased the knowledge on the diversity and importance of benthic diatoms in complex real-world environments. Some of the diversity patterns were general and non-dependent of spatial scale, whereas others were highly variable between regions and gradients. The results emphasize the need to consider the effect of benthic diatoms when modelling and designing the management of coastal areas, and indicate the usefulness of studies with environmentally and spatially large gradients for the understanding of diversity patterns in natural ecosystems.Piilevät ovat erittäin monimuotoinen ryhmä mikroskooppisia leviä, joilla on koko maapallon kannalta elintärkeitä tehtäviä. Merissä elävät piilevät muun muassa tuottavat suuren osan maapallon ilmakehän hapesta. Merissä ja murtovesissä, kuten Itämeressä, elävien piilevien monimuotoisuudesta ja sen vaikutuksesta elinympäristön toimintaan tiedetään kuitenkin vasta vähän. Tässä väitöskirjassa selvitettiin Itämeren rannikkoalueiden pohjilla elävien piilevien monimuotoisuuden vaikutusta ekosysteemien kykyyn tuottaa biomassaa, monimuotoisuuden vaihtelua ajan ja paikan suhteen erilaisissa ympäristöissä sekä monimuotoisuuteen vaikuttavia ympäristötekijöitä. Piilevien monimuotoisuus vaihteli alueellisesti mutta oli tärkeää koko elinympäristön toiminnalle, sillä se muodosti alarajan ekosysteemin kyvylle tuottaa biomassaa. Toisin sanoen piileväyhteisön monimuotoisuuden ollessa pieni ekosysteemien tuottavuus oli vaihteleva, mutta kun monimuotoisuuden oli suuri, ekosysteemien tuottavuus oli säännöllisesti korkea. Piilevien ß-diversiteettiä eli sitä, miten erilaisia piileväyhteisöt ovat näytteenottoalueen eri osissa, tutkittiin usealla suuruudeltaan erilaisella alueella. Tulokset pysyivät alueen koosta riippumatta samankaltaisina: näytteenottoalueiden eri päissä piileväyhteisöt olivat lajistoltaan lähes täysin erilaisia, mutta lajipiirteiltään eli toiminnaltaan melko samankaltaisia. Ympäristömuuttujien vaikutusta tutkittaessa havaittiin, että se, mitkä muuttujat olivat tärkeitä piileväyhteisöille, vaihteli alueelta toiselle. Alueiden välisten erojen huomioiminen on siis tärkeää esimerkiksi ympäristön suojelutoimia suunniteltaessa. Ajallista vaihtelua tutkittaessa todettiin, että piileväyhteisöjen koostumus vaihteli huomattavasti vuodenaikojen ja vuosien välillä, kun taas monimuotoisuus pysyi melko samankaltaisena. Monimuotoisuus oli kuitenkin alhaisin sellaisena talvena, jolloin sää oli poikkeuksellisen lämmin ja jääpeiteaika lyhyt. Ilmaston lämpeneminen saattaa siis heikentää pohjalla elävien eliöyhteisöjen monimuotoisuutta. Tämä väitöskirja on tuottanut uutta tietoa pohjalla elävien piilevien monimuotoisuudesta monimutkaisissa ja vaihtelevissa luonnonympäristöissä. Piilevien monimuotoisuuden todettiin olevan tärkeää koko elinympäristön toiminnalle, ja sen vaikutus tulisikin tulevaisuudessa ottaa huomioon esimerkiksi suunniteltaessa rannikkoalueiden hyödyntämistä ja suojelua

Veden laadun, ilmaston ja sijainnin vaikutukset piileväyhteisöihin pohjoisella Itämerellä

The structure of a local community depends on interacting local and regional filters. During the last few decades, the effects of local and regional factors have been studies in communities formed not only by macro-organisms but also by micro-organisms like diatoms. In the northern parts of the Baltic Sea, unfortunately, this kind of research has been quite scarce and often spatially limited. Studying of brackish water seas like the Baltic Sea is important, however, because their conditions and species composition differ from those of oceans, lakes and rivers, and their biodiversity is usually quite low. Also, they are surrounded by continents and are therefore exposed to heavy pollution. The goal of this thesis is to examine what are the most important factors explaining the species richness and species composition of the epilithic diatom communities in the littoral zone of the Gulf of Finland and the Gulf of Bothnia, Baltic Sea. The explaining factors used in the study are water chemistry, salinity, climate, exposition and geographical location. The diatom and water samples were collected in July 2013 from 37 sites covering the whole Finnish coastline of the Gulf of Finland and the Gulf of Bothnia. Also data received from the Finnish Meteorological Institute and the Finnish Environment Institute were used after interpolation. Generalized linear models (GLM) and generalized additive models (GAM) were used for the species richness analyses, and the spatial autocorrelation was examined with Moran's I -index. The species composition of the communities was analyzed with variation partitioning, redundancy analysis and Mantel's test. According to the GLMs, the species richness was best explained by total nitrogen, pH and oxygen. According to the GAMs, the best explaining factors were pH, oxygen and salinity. Species richness was not spatially autocorrelated. The variation partitioning showed that the species composition was mostly affected by climate and location, whereas water quality had little impact. However, the strongest affecting factor was the cooperative action of water quality, climate and location. According to the Mantel's test, there was a statistically significant correlation between species composition and geographical location, whereas between species composition and water quality or species composition and climate the correlations were non-significant. The redundancy analysis indicated that the most important factors regulating the species composition were air temperature, silicon oxide, total phosphorus, water temperature, salinity and pH. The results suggest that the species richness of the diatom communities in the northern Baltic Sea is mostly regulated by the local factors, while geographical location and climate have little impact. When it comes to the species composition, geographical location has stronger effect than water quality or climate. However, the most important regulator of species composition is the cooperative action of water quality, climate and location, because location affects climate and both location and climate affect water quality.Paikallisen eliöyhteisön rakenne riippuu paikallisista ja alueellisista suodattimista, jotka toimivat vuorovaikutuksessa keskenään. Paikallisten ja alueellisten tekijöiden vaikutuksia on viime vuosikymmeninä tutkittu makro-organismien lisäksi myös mikro-organismien, kuten piilevien, muodostamissa eliöyhteisöissä. Pohjoisella Itämerellä tällainen tutkimus on kuitenkin ollut vähäistä ja näytteenotto on useimmiten keskittynyt spatiaalisesti suppealle alueelle. Itämeren kaltaisten murtovesialtaiden tutkiminen on kuitenkin tärkeää, koska ne eroavat olosuhteiltaan ja eliöstöltään muista vesialueista ja niiden biodiversiteetti on yleensä alhaisempi kuin valtamerien ja makeiden vesien. Lisäksi ne ovat mannerten ympäröimiä ja altistuvat siksi voimakkaalle ihmisvaikutukselle. Tämän tutkimuksen tavoitteena on selvittää, mitkä ovat tärkeimmät Suomenlahden ja Pohjanlahden epiliittisten litoraalipiileväyhteisöjen lajikoostumusta ja lajimäärää selittävät tekijät. Selittävinä tekijöinä käytetään vesikemia-, suolapitoisuus- ja ilmastogradientteja, rannan avoimuutta ja maantieteellistä sijaintia. Piilevä- ja vesinäytteet kerättiin vuoden 2013 heinäkuun aikana 37 näytepaikasta siten, että näytesarja kattoi koko Suomenlahden ja Pohjanlahden Suomen puoleiset rannikot. Lisäksi käytettiin Ilmatieteenlaitoksen ja Suomen Ympäristökeskuksen interpoloituja ilmasto- ja vedenlaatuaineistoja. Lajirunsausanalyysit tehtiin yleistettyjen lineaaristen (GLM) ja yleistettyjen additiivisten (GAM) mallien avulla, ja spatiaalista autokorrelaatiota tarkasteltiin Moranin I -indeksillä. Lajistoanalyyseissä käytettiin hajonnan ositusta, redundanssianalyysiä ja Mantelin testiä. GLM-mallien mukaan lajirunsautta selittivät parhaiten kokonaistyppi, pH ja happi ja GAM-mallien mukaan pH, happi ja suolapitoisuus. Lajirunsaus ei ollut spatiaalisesti autokorreloitunut. Lajiston koostumukseen vaikuttivat hajonnan osituksen mukaan eniten ilmasto- ja sijaintimuuttujat, kun taas vedenlaatumuuttujien vaikutus oli pieni. Tärkein tekijä oli kuitenkin vedenlaatu-, ilmasto- ja sijaintimuuttujien yhteisvaikutus. Mantelin testi osoitti, että piilevälajistolla ja maantieteellisellä sijainnilla oli tilastollisesti merkitsevä korrelaatio, mutta lajiston ja vedenlaadun tai lajiston ja ilmaston välillä sellaista ei esiintynyt. Redundanssianalyysin mukaan tärkeimpiä lajiston koostumusta selittäviä tekijöitä olivat ilman lämpötila, piioksidi, kokonaisfosfori, veden lämpötila, suolapitoisuus ja pH. Tämän tutkimuksen tulosten perusteella voidaan todeta, että pohjoisen Itämeren piileväyhteisöjen lajirunsautta säätelevät voimakkaimmin paikalliset tekijät eikä alueellisella sijainnilla tai ilmastolla ole suurta vaikutusta. Lajiston säätelijänä maantieteellinen sijainti on sen sijaan tärkeämpi kuin vedenlaatu tai ilmasto. Voimakkaimmin lajistoon vaikuttaa kuitenkin vedenlaadun, ilmaston ja sijainnin yhteisvaikutus, koska sijainti vaikuttaa ilmastoon ja sekä sijainti että ilmasto vaikuttavat vedenlaatuun

Studying biodiversity-ecosystem function relationships in experimental microcosms among islands

Ecological studies on islands have provided fundamental insights into the mechanisms underlying biodiversity of larger organisms, but we know little about the factors affecting island microbial biodiversity and ecosystem function. We conducted a field experiment on five Baltic Sea islands where we placed aquatic microcosms with different levels of salinity mimicking environmental stress and allowed diatoms to colonize the microcosms via the air. Using structural equation models (SEM), we investigated the interconnections among environmental and dispersal-related factors, diatom biodiversity, and ecosystem productivity (represented by chlorophyll a concentration). We also tested whether the body size structure of the community influences productivity together with biodiversity. In SEMs, we found no relationship between species richness or evenness and productivity. However, productivity increased with increasing mean body size of species in the communities. The effects of environmental stress on both biodiversity and ecosystem productivity were highlighted as species richness and evenness declined, whereas productivity increased at the highest salinity levels. In addition to salinity, wind exposure affected both biodiversity metrics and productivity. This study provides new insights into microbial community assembly in a field experimental setting and the relationship between biodiversity and ecosystem function. Our results indicate that salinity presents a strong abiotic filter, leading to communities that may be species poor, yet comprise salinity-tolerant and relatively productive species at high salinity. Our findings also emphasize the importance of mean community body size in mediating the effects of environmental conditions on productivity and suggest that this trait should be considered more broadly in biodiversity-ecosystem function studies.Peer reviewe

Stable seasonal and annual alpha diversity of benthic diatom communities despite changing community composition

The global biodiversity loss has raised interest in the different facets of diversity, and the importance of diversity for ecosystem functions has been recognized. However, our knowledge on seasonal and inter-annual variation in the composition and diversity of communities is still poor. Here, we investigated the seasonal and inter-annual changes in taxonomic and functional community composition and diversity of benthic diatoms in a coastal habitat of the northern Baltic Sea, where seasonal and inter-annual variation of climate is pronounced. We found that the taxonomic and functional alpha diversity remained stable at seasonal and inter-annual level despite strong changes in community composition. However, alpha diversity decreased during an exceptionally warm winter possibly due to disturbances induced by the lack of ice. This may suggest that climate warming and consequently limited ice cover will affect the diversity of benthic communities.Peer reviewe

Diversity and distribution across a large environmental and spatial gradient: Evaluating the taxonomic and functional turnover, transitions and environmental drivers of benthic diatom communities

Aim Global biodiversity loss has raised interest in understanding variation in diversity at different scales. In particular, studies conducted across large spatial gradients are crucial, because they can increase perspectives on how ecological patterns change relative to environmental factors and facilitate predictions of possible responses to environmental change. We explored the full extent of a brackish sea to test the hypotheses that: (a) benthic communities are defined by the limited ranges of species, controlled by varying drivers along a large environmental gradient; (b) the responses of taxonomic and functional community composition and turnover to the environmental gradient are different, thus highlighting the need to include both measures in ecological studies; and (c) diversity reaches the minimum at intermediate salinities (Remane curve) owing to the low adaptation of freshwater and marine species. Location A large environmental and spatial gradient spanning the entire Swedish coastline (c. 2,300 km; salinity 1.2-27.6), the Baltic Sea. Time period August 2018. Major taxa studied Benthic diatoms. Methods We assessed environmental drivers for the communities and calculated the taxonomic and functional alpha and beta diversity along the gradient. We also compared the taxonomic and functional composition and diversity of communities among areas with different salinity. Results We found support for the hypothesis of limited species ranges, because taxonomic beta diversity, mainly induced by changes in salinity and climate, was high, whereas functional beta diversity remained considerably lower, and the composition and diversity of communities, in addition to environmental drivers controlling the communities, differed between regions with different salinity. The lowest taxonomic diversity was found at intermediate salinities of 5-6. Main conclusions These findings advance understanding of large-scale patterns of benthic diversity, emphasize the importance of large gradient studies for a better understanding of general ecological patterns and highlight the vulnerability of brackish water ecosystems as ecologically important tipping-point realms.Peer reviewe

Factors influencing the biodiversity of three microbial groups within and among islands of the Baltic Sea

Islands provide ideal model systems to examine the factors influencing biodiversity, yet knowledge of microbial biodiversity on islands remains scarce. We collected a dataset from 101 rock pools along a freshwater to brackish water transition on islands of the Baltic Sea and investigated the patterns and drivers of community composition and species richness of diatoms, cyanobacteria and non-cyanobacteria bacteria among islands. We also examined whether environmental heterogeneity increased beta diversity and species richness within islands. Among islands, the patterns in community composition were concordant among the microbial groups, with distinct changes along the freshwater-brackish gradient. The patterns in species richness were context-dependent for each microbial group. In general, richness patterns were most strongly associated with nutrient concentrations or the distances to potential sources of immigrants, whereas no positive relationships between ecosystem size and richness were found. Within islands, environmental heterogeneity was positively correlated with the beta diversity of each microbial group, but not species richness. Our findings provide novel insights into the factors influencing microbial biodiversity. The results suggest that island microbial biodiversity patterns are influenced by species sorting and dispersal-related mechanisms and highlight the importance of environmental heterogeneity for beta diversity.Peer reviewe

Trends in Early Outpatient Drug Therapy in Pediatric Inflammatory Bowel Disease in Finland: A Nationwide Register-Based Study in 1999–2009

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