World Wide Web korpuksena kielitieteellisen tutkimusaineiston haku verkkosivuilta

Tämä tutkielma käsittelee World Wide Webin sisältämien verkkosivujen sisältöjen käyttöä korpusmaisesti kielitieteellisenä tutkimusaineistona. World Wide Web sisältää moninkertaisesti enemmän tekstiä kuin suurimmat olemassa olevat perinteiset tekstikorpukset, joten verkkosivuilta voi todennäköisesti löytää paljon esiintymiä sellaisista sanoista ja rakenteista, jotka ovat perinteisissä korpuksissa harvinaisia. Verkkosivuja voidaan käyttää aineistona kahdella eri tavalla: voidaan kerätä satunnainen otos verkkosivuista ja luoda itsenäinen korpus niiden sisällöistä, tai käyttää koko World Wide Webiä korpuksena verkkohakukoneiden kautta. Verkkosivuja on käytetty tutkimusaineistona monilla eri kielitieteen aloilla, kuten leksikograafisessa tutkimuksessa, syntaktisten rakenteiden tutkimuksessa, pedagogisena materiaalina ja vähemmistökielten tutkimuksessa. Verkkosivuilla on perinteisiin korpuksiin verrattuna useita haitallisia ominaisuuksia, jotka pitää ottaa huomioon, kun niitä käytetään aineistona. Kaikki sivut eivät sisällä kelvollista tekstiä, ja sivut ovat usein esimerkiksi HTML-muotoisia, jolloin ne pitää muuttaa helpommin käsiteltävissä olevaan muotoon. Verkkosivut sisältävät enemmän kielellisiä virheitä kuin perinteiset korpukset, ja niiden tekstityypit ja aihepiirit ovat runsaslukuisempia kuin perinteisten korpusten. Aineiston keräämiseen verkkosivuilta tarvitaan tehokkaita ohjelmatyökaluja. Näistä yleisimpiä ovat kaupalliset verkkohakukoneet, joiden kautta on mahdollista päästä nopeasti käsiksi suureen määrään erilaisia sivuja. Näiden lisäksi voidaan käyttää erityisesti kielitieteellisiin tarpeisiin kehitettyjä työkaluja. Tässä tutkielmassa esitellään ohjelmatyökalut WebCorp, WebAsCorpus.org, BootCaT ja Web as Corpus Toolkit, joiden avulla voi hakea aineistoa verkkosivuilta nimenomaan kielitieteellisiin tarkoituksiin.

Teaching in Higher Education : From Content-focused to Learning-focused Approaches to Teaching

The aim of this dissertation was to explore teaching in higher education from the teachers’ perspective. Two of the four studies analysed the effect of pedagogical training on approaches to teaching and on self-efficacy beliefs of teachers on teaching. Of these two studies, Study I analysed the effect of pedagogical training by applying a cross-sectional setting. The results showed that short training made teachers less student-centred and decreased their self-efficacy beliefs, as reported by the teachers themselves. However, more constant training enhanced the adoption of a student-centred approach to teaching and increased the self-efficacy beliefs of teachers as well. The teacher-focused approach to teaching was more resistant to change. Study II, on the other hand, applied a longitudinal setting. The results implied that among teachers who had not acquired more pedagogical training after Study II there were no changes in the student-focused approach scale between the measurements. However, teachers who had participated in further pedagogical training scored significantly higher on the scale measuring the student-focused approach to teaching. There were positive changes in the self-efficacy beliefs of teachers among teachers who had not participated in further training as well as among those who had. However, the analysis revealed that those teachers had the least teaching experience. Again, the teacher-focused approach was more resistant to change. Study III analysed approaches to teaching qualitatively by using a large and multidisciplinary sample in order to capture the variation in descriptions of teaching. Two broad categories of description were found: the learning-focused and the content-focused approach to teaching. The results implied that the purpose of teaching separates the two categories. In addition, the study aimed to identify different aspects of teaching in the higher-education context. Ten aspects of teaching were identified. While Study III explored teaching on a general level, Study IV analysed teaching on an individual level. The aim was to explore consonance and dissonance in the kinds of combinations of approaches to teaching university teachers adopt. The results showed that some teachers were clearly and systematically either learning- or content-focused. On the other hand, profiles of some teachers consisted of combinations of learning- and content-focused approaches or conceptions making their profiles dissonant. Three types of dissonance were identified. The four studies indicated that pedagogical training organised for university teachers is needed in order to enhance the development of their teaching. The results implied that the shift from content-focused or dissonant profiles towards consonant learning-focused profiles is a slow process and that teachers’ conceptions of teaching have to be addressed first in order to promote learning-focused teaching.

Sense of Community in Web Environment

The study of social phenomena in the World Wide Web has been rather fragmentary, andthere is no coherent, reseach-based theory about sense of community in Web environment. Sense of community means part of one's self-concept that has to do with perceiving oneself belonging to, and feeling affinity to a certain social grouping. The present study aimed to find evidence for sense of community in Web environment, and specifically find out what the most critical psychological factors of sense of community would be. Based on known characteristics of real life communities and sense of community, and few occational studies of Web-communities, it was hypothesized that the following factors would be the most critical ones and that they could be grouped as prerequisites, facilitators and consequences of sense of community: awareness and social presence (prerequisites), criteria for membership and borders, common purpose, social interaction and reciprocity, norms and conformity, common history (facilitators), trust and accountability (consequences). In addition to critical factors, the present study aimed to find out if this kind of grouping would be valid. Furthermore, the effect of Web-community members' background variables to sense of community was of interest. In order to answer the questions, an online-questionnaire was created and tested. It included propositions that reflect factors that precede, facilitate and follow the sense of community in Web environment. A factor analysis was calculated to find out the critical factors and analyses of variance were calculated to see if the grouping to prerequisites, facilitators and consequences was right and how the background variables would affect the sense of community in Web environment. The results indicated that the psychological structure of sense of community in Web environment could not be presented with critical variables grouped as prerequisites, facilitators and consequences. Most factors did facilitate the sense of community, but based on this data it could not be argued that some of the factors chronologically precedesense of community and some follow it. Instead, the factor analysis revealed that the most critical factors in sense of community in Web environment are 1) reciprocal involvement, 2) basic trust for others, 3) similarity and common purpose of members, and 4) shared history of members. The most influencing background variables were the member's own participation activity (indicated with reading and writing messages) and the phase in membership lifecycle (from visitor to leader). The more the member participated and the further in membership life cycle he was, the more he felt sense of community. There are many descreptions of sense of community, but the present study was one of the first to actually measure the phenomenon in Web environment, and that gained well documented, valid results based on large data, proving that sense of community in Web environment is possible, and clarifying its psychological structure, thus enhancing the understanding of sense of community in Web environment. Keywords: sense of community, Web-community, psychology of the Internet

Widening Perspectives of Teacher Education : Studies on theory-practice relationship, reflection, research and professional development

This dissertation examined the research-based teacher education at the University of Helsinki from different theoretical and practical perspectives. Five studies focused on these perspectives separately as well as overlappingly. Study I focused on the reflection process of graduating teacher students. The data consisted of essays the students wrote as their last assignment before graduating, where their assignment was to examine their development as researchers during their MA thesis research process. The results indicated that the teacher students had analysed their own development thoroughly during the process and that they had reflected on theoretical as well as practical educational matters. The results also pointed out that, in the students’ opinion, personally conducted research is a significant learning process. -- Study II investigated teacher students’ workplace learning and the integration of theory and practice in teacher education. The students’ interviews focused on their learning of teacher’s work prior to education. The interviewees’ responses concerning their ‘surviving’ in teaching prior to teacher education were categorized into three categories: learning through experiences, school as a teacher learning environment, and case-specific learning. The survey part of the study focused on integration of theory and practice within the education process. The results showed that the students who worked while they studied took advantage of the studies and applied them to work. They set more demanding teaching goals and reflected on their work more theoretically. -- Study III examined practical aspects of the teacher students’ MA thesis research as well as the integration of theory and practice in teacher education. The participants were surveyed using a web-based survey which dealt with the participants’ teacher education experiences. According to the results, most of the students had chosen a practical topic for their MA thesis, one arising from their work environment, and most had chosen a research topic that would develop their own teaching. The results showed that the integration of theory and practice had taken place in much of the course work, but most obviously in the practicum periods, and also in the courses concerning the school subjects. The majority felt that the education had in some way been successful with regards to integration. -- Study IV explored the idea of considering teacher students’ MA thesis research as professional development. Twenty-three teachers were interviewed on the subject of their experiences of conducting research about their own work as teachers. The results of the interviews showed that the reasons for choosing the MA thesis research topic were multiple: practical, theoretical, personal, professional reasons, as well as outside effect. The objectives of the MA thesis research, besides graduating, were actual projects, developing the ability to work as teachers, conducting significant research, and sharing knowledge of the topic. The results indicated that an MA thesis can function as a tool for professional development, for example in finding ways for adjusting teaching, increasing interaction skills, gaining knowledge or improving reflection on theory and/or practice, strengthening self-confidence as a teacher, increasing researching skills or academic writing skills, as well as becoming critical and being able to read scientific and academic literature. -- Study V analysed teachers’ views of the impact of practitioner research. According to the results, the interviewees considered the benefits of practitioner research to be many, affecting teachers, pupils, parents, the working community, and the wider society. Most of the teachers indicated that they intended to continue to conduct research in the future. The results also showed that teachers often reflected personally and collectively, and viewed this as important. -- These five studies point out that MA thesis research is and can be a useful tool for increasing reflection doing with personal and professional development, as well as integrating theory and practice. The studies suggest that more advantage could be taken of the MA thesis research project. More integration of working and studying could and should be made possible for teacher students. This could be done in various ways within teacher education, but the MA thesis should be seen as a pedagogical possibility.

Ongelmana yhteistyökyvyttömyys? : Teoreettisen ymmärryksen etsintää web-avusteiselle tiedontuottamisyhteistyölle

Tutkimuksessa analysoidaan teoriatasolla web-avusteisen tiedontuottamisyhteistyön kokeilutoiminnassa esiin tulleita ongelmia ja kootaan niiden viitoittamana teoriaperustaa tulevaisuuden työskentelytavalle, tietämyksen web-avusteiselle ryhmäprosessoinnille. Keskiössä on ihminen kognitiivisena tiedonkäsittelijänä ja elinikäisenä oppijana. Organisaatiossa vallitsevat toimintastrategiat, ryhmätyöskentelyn organisointi ja ryhmässä toteutuvat käytännöt muodostavat yksilön toimintaa ohjaavan sosiaalisen toimintaympäristön, joka säätelee yhteistyöprosessin onnistumista. Yhteistyötä tarkastellaan sosiaalisen tiedonkäsittelyn ryhmäilmiönä, jossa käsite yhteistyökyky kyseenalaistuu. Tuotetussa teoriaperustassa ihminen nähdään monitasoisten oppimishaasteiden ristitulessa. Koulutuksessa vallitseva absoluuttinen tietokäsitys on pystyttävä muuttamaan konstruktivistiseksi tietokäsitykseksi: yhteistä tietämystä ryhmänä tuotettaessa yksilöiden tietämys on rakennusaineena. Koulussa saatu sosiaalisen tiedonkäsittelyn malli, itsekeskeisen tiedonkäsittelyn malli, ei sovellu tietämyksen ryhmäprosessointiin. Malliin liittyviä oppeja on poisopittava samalla kun ryhmäjäsenenä on suunniteltava ja yhdessä opeteltava ryhmäkeskeisiä ja web-avusteisia tiedonkäsittelymalleja. Näin yhteistyöprosessissa toteutuu rinnakkain asiaoppimista ja toimintaoppimista. Näitä molempia on tarpeen tukea kehitettäessä uudenlaisia web-avusteisia työskentelymenetelmiä. Osassa I esitellään tutkimuksen kokemusperäisiä virikkeitä. Suhteellisen tietokäsityksen mukaisesti tämä tutkimus on kiinteästi kytkeytynyt tutkijan elinikäiseen oppimiseen ja tutkimus kuvataan tutkijan yksilöllisen tietämyksen prosessointina. Tutkimusaiheen löytymiseen johtaneet käytännön havainnot aloittavat sen takia raportoinnin. Erityisesti koulun sosiaalisen tiedonkäsittelyn organisointi on tarkastelun kohteena. Osassa II hahmotetaan tutkimusnäkökulmaa. Tutkimuskysymykset ovat lähinnä viitoittamassa tietämyksen etsintää. Tutkimusmenetelmä, kokeilutoiminnan analysointi, on saanut vahvasti vaikutteita toimintatutkimuksesta. Tutkimusasetelman perustana on toimintaan kytkeytyvä ihmiskäsitys. Kirjallisuuden avulla etsitään mahdollisia kytkeytymiä ihmisen käyttäytymisen ja sosiaalisen toiminnan organisoinnin välillä. Osa III kuvailee tutkimusaihetta koskevan ymmärryksen prosessointia. Esiymmärrys yhteistyöstä ja yhteistyökäsitteen määrittely mahdollistavat kokeilutoimintaan ryhtymisen. Uusi viestintämahdollisuus (www) nähdään yhteisessä tiedonkäsittelyssä apuvälineenä. Käytännön kokeilujaksot tarjoavat aineksia kognitiivisen tiedonkäsittelyn syvällisten periaatteiden löytymiselle. Inhimillinen toiminta ja sosiaalinen tiedonkäsittely saavat teoriatason analysoinnissa oppimiseen perustuvia tulkintoja. Osassa IV esitellään tutkimuksen tavoitteena ollutta teoriaperustaa tietämyksen web-avusteiselle ryhmäprosessoinnille. Teoriatiivistelmässä keskiöön nousee ihmisen kognitiivinen tiedonkäsittely sekä konstruktivistisen asiaoppimisen että selviytymispainotteisen toimintaoppimisen muodossa. Sosiaalinen toimintaympäristö nähdään osallisena kognitiivisessa tiedonkäsittelyssä ja selityksenä sille, että yhteinen tiedonkäsittely ei onnistu pelkästään tietoverkkoympäristössä vaan tarvitaan myös sosiaalisia tapaamisia. Kokeilutoiminnan opetuksia tuodaan esille yhteistyöprosessin keskeisten tapahtumien tarkastelussa. Tuotettua teoriaperustaa koetellaan tieteen kentällä vertailemalla sitä muiden tutkijoiden julkaisemiin käsityksiin. Tietoverkkoteknologian suhdetta inhimilliseen tiedonkäsittelyyn verrataan muualla saatuihin ja julkaistuihin käsityksiin. Avainsanat: tietointensiivinen yhteistyö, tiedontuottamisyhteistyö, yhteistyöprosessi, yhteistyökyky, yhteistyökyvyttömyys, virtuaalinen yhteistyöorganisaatio, yksilöllinen tietämys, yhteisen ymmärryksen etsintä, yhteinen tietämys, kognitiivinen tiedonkäsittely, asiaoppiminen, toimintaoppiminen, sosiaalinen tiedonkäsittely, sosiaalinen toimintaympäristö, automatisoitunut toimintamalli, yksilökeskeinen toimintamalli, itsekeskeinen toimintamalli, ryhmäkeskeinen toimintamalli, sosiaalisen tiedonkäsittelyn toimintastrategia, työympäristössä oppiminen.

Semanttisen webin ontologisen tekstiilikäsitteistön kehittäminen ja liittäminen museoiden luettelointitietoihin

DEVELOPING A TEXTILE ONTOLOGY FOR THE SEMANTIC WEB AND CONNECTING IT TO MUSEUM CATALOGING DATA The goal of the Semantic Web is to share concept-based information in a versatile way on the Internet. This is achievable using formal data structures called ontologies. The goal of this re-search is to increase the usability of museum cataloging data in information retrieval. The work is interdisciplinary, involving craft science, terminology science, computer science, and museology. In the first part of the dissertation an ontology of concepts of textiles, garments, and accessories is developed for museum cataloging work. The ontology work was done with the help of thesauri, vocabularies, research reports, and standards. The basis of the ontology development was the Museoalan asiasanasto MASA, a thesaurus for museum cataloging work which has been enriched by other vocabularies. Concepts and terms concerning the research object, as well as the material names of textiles, costumes, and accessories, were focused on. The research method was terminological concept analysis complemented by an ontological view of the Semantic Web. The concept structure was based on the hierarchical generic relation. Attention was also paid to other relations between terms and concepts, and between concepts themselves. Altogether 977 concept classes were created. Issues including how to choose and name concepts for the ontology hierarchy and how deep and broad the hierarchy could be are discussed from the viewpoint of the ontology developer and museum cataloger. The second part of the dissertation analyzes why some of the cataloged terms did not match with the developed textile ontology. This problem is significant because it prevents automatic ontological content integration of the cataloged data on the Semantic Web. The research datasets, i.e. the cataloged museum data on textile collections, came from three museums: Espoo City Museum, Lahti City Museum and The National Museum of Finland. The data included 1803 textile, costume, and accessory objects. Unmatched object and textile material names were analyzed. In the case of the object names six categories (475 cases), and of the material names eight categories (423 cases), were found where automatic annotation was not possible. The most common explanation was that the cataloged field was filled with a long sentence comprised of many terms. Sometimes in the compound term, the object name and material, or the name and the way of usage, were combined. As well, numeric values in the material name cataloging field prevented annotation and so did the absence of a corresponding concept in the ontology. Ready-made drop-down lists of materials used in one cataloging system facilitated the annotation. In the case of naming objects and materials, one should use terms in basic form without attributes. The developed textile ontology has been applied in two cultural portals, MuseumFinland and Culturesampo, where one can search for and browse information based on cataloged data using integrated ontologies in an interoperable way. The textile ontology is also part of the national FinnONTO ontology infrastructure. Keywords: annotation, concept, concept analysis, cataloging, museum collection, ontology, Semantic Web, textile collection, textile material

Consumers and the conceptual and practical appropriation of functional foods

Taking the appropriation of objects as a theoretical starting point, this study makes a distinction between a conceptual and practical level of adopting new objects and products in everyday life. The study applies the concept of appropriation in social food research and examines consumers appropriation of functional foods, i.e., foods developed to improve health and well-being or reduce the risk of disease beyond the usual nutritional effects of foods. The study uses the concept of appropriation to understand the adoption and the process of making functional foods our own . First, the study focuses on the conceptual appropriation by analysing consumers interpretations and opinions on functional foods. Second, it analyses the use of functional foods and examines the role of sociodemographic and food- and health-related background factors in the use of functional foods. Both quantitative and qualitative data were used in the study. Altogether 1210 Finns representative of the population took part in a survey carried out in 2002 as computer-assisted telephone interviews (CATI). The survey examined the acceptability and use of functional foods in Finland. In 2004, eight focus group discussions were organised for 45 users and non-users of cholesterol-lowering spreads. The qualitative study focused on consumers interpretative perspectives on healthy eating and functional foods. The findings are reported in four original articles and a summary article. The results show that the appropriation of functional foods is a multifaceted phenomenon. The conceptual appropriation is related to consumers interpretations of functional foods in the context of healthy foods and healthy eating; their trust in the products, their manufacturers, research and control; and the relationship of functional foods and the ideal of natural foods. The analysis of the practical appropriation of four different types of foods marketed as functional showed that there are sociodemographic differences between users and non-users of the products, but more importantly, the differences are related to consumers food- and health-related views and practices. Consumers ways of appropriating functional foods in the conceptual and practical sense take shape in a complex web of ideas and everyday practices concerning food, health and eating as a whole. The results also indicate that the conceptual and practical appropriation are not necessarily uniform or coherent processes. Consumers interpret healthy eating and functional foods from a variety of perspectives and there is a multiplicity of rationales of using functional foods. Appropriation embraces many opposing dimensions simultaneously: good experiences and doubts, approval and criticism, expectations and things taken for granted.

TCP Performance in Heterogeneous Wireless Networks

The TCP protocol is used by most Internet applications today, including the recent mobile wireless terminals that use TCP for their World-Wide Web, E-mail and other traffic. The recent wireless network technologies, such as GPRS, are known to cause delay spikes in packet transfer. This causes unnecessary TCP retransmission timeouts. This dissertation proposes a mechanism, Forward RTO-Recovery (F-RTO) for detecting the unnecessary TCP retransmission timeouts and thus allow TCP to take appropriate follow-up actions. We analyze a Linux F-RTO implementation in various network scenarios and investigate different alternatives to the basic algorithm. The second part of this dissertation is focused on quickly adapting the TCP's transmission rate when the underlying link characteristics change suddenly. This can happen, for example, due to vertical hand-offs between GPRS and WLAN wireless technologies. We investigate the Quick-Start algorithm that, in collaboration with the network routers, aims to quickly probe the available bandwidth on a network path, and allow TCP's congestion control algorithms to use that information. By extensive simulations we study the different router algorithms and parameters for Quick-Start, and discuss the challenges Quick-Start faces in the current Internet. We also study the performance of Quick-Start when applied to vertical hand-offs between different wireless link technologies.

Luottamuksenhallinta web-palveluympäristössä

Tutkielmassa käsitellään luottamuksenhallintaa web-palveluympäristössä. Dynaaminen toimintaympäristö asettaa vaatimuksia luottamuksenhallintajärjestelmälle, jota käytetään paitsi paikallisten pääsynhallintapäätösten tekemiseen, myös laajemman mittakaavan päätöksenteon tukena, useiden autonomisten toimijoiden muodostamien yhteisöjen hallinnassa. Tutkielma esittelee Trust Based on Evidence -projektissa kehitetyn luottamuksenhallintajärjestelmän tiedollisen ja toiminnallisen mallin, paikallisesta ja yhteisön näkökulmasta. Mallia selkeytetään web-palveluympäristöön sijoittuvan esimerkin avulla. Luottamuksen käsitteen rakentamiseksi esitellään myös eri osa-alueille sijoittuvia luottamuksen malleja ja luottamusta käyttäviä järjestelmiä. Avoimessa verkkoympäristössä palveluntarjoaja joutuu tasapainottelemaan kahden osin vastakkaisen tavoitteen välillä: toisaalta järjestelmän tulisi olla mahdollisimman avoin, jotta se houkuttelisi käyttäjiä, toisaalta liiallinen avoimuus kasvattaa tietomurron riskiä. Kompromissin löytäminen on hankaloitunut edelleen saavutettavien käyttäjien määrän kasvaessa ja tarjottavien palvelujen monimutkaistuessa. Tehtävä vaatii toisaalta erikoistapauksien käsittelyä, toisaalta yleistettävyyttä laajan käyttäjistön suhteen. Tietoturvan ylläpidon automatisointia ovat edistäneet muun muassa politiikkapäätösten erottaminen toteutuksesta ja mahdollisten tietomurron merkkien tarkkailun delegointi siihen erikoistuneille ohjelmille (IDS). Palvelujen käyttäjistön kasvaessa ja siirtyessä nimettömämmiksi kurinpito ja tarkkailu kuitenkin vaikeutuvat entisestään, eikä ylläpitäjiä riitä sidottavaksi jatkuvaan käyttäjien vahtimiseen. Monesti valvoja voikin vain poistaa käyttöoikeuden häiriköltä, jolloin esimerkiksi hieman lievemmälle sääntöjen ``venyttämiselle'' ei juuri voi tehdä mitään. Luottamuksenhallinta helpottaa rikkomuksiin ja toisaalta hyvään käytökseen reagoimista asteittain. Sen pohjalta käyttäjien valvontaan, pääsynhallintaan ja resurssien rajoitukseen liittyvä hienosäätö voidaan tuoda ymmärrettäväksi osaksi ylläpitoa ja pitkälti myös automatisoida. Avainsanat: luottamuksenhallinta, Web Services

Harmful algae in the planktonic food web of the Baltic Sea

This study deals with algal species occurring commonly in the Baltic Sea: haptophyte Prymnesium parvum, dinoflagellates Dinophysis acuminata, D. norvegica and D. rotundata, and cyanobacterium Nodularia spumigena. The hypotheses are connected to the toxicity of the species, to the factors determining toxicity, to the consequences of toxicity and to the transfer of toxins in the aquatic food web. Since the Baltic Sea is severely eutrophicated, the fast-growing haptophytes have potential in causing toxic blooms. In our studies, the toxicity (as haemolytic activity) of the haptophyte P. parvum was highest under phosphorus-limited conditions, but the cells were toxic also under nitrogen limitation and under nutrient-balanced growth conditions. The cellular nutrient ratios were tightly related to the toxicity. The stoichiometric flexibility for cellular phosphorus quota was higher than for nitrogen, and nitrogen limitation led to decreased biomass. Negative allelopathic effects on another algae (Rhodomonas salina) could be observed already at low P. parvum cell densities, whereas immediate lysis of R. salina cells occurred at P. parvum cell densities corresponding to natural blooms. Release of dissolved organic carbon from the R. salina cells was measured within 30 minutes, and an increase in bacterial number and biomass was measured within 23 h. Because of the allelopathic effect, formation of a P. parvum bloom may accelerate after a critical cell density is reached and the competing species are eliminated. A P. parvum bloom indirectly stimulates bacterial growth, and alters the functioning of the planktonic food web by increasing the carbon transfer through the microbial loop. Our results were the first reports on DSP toxins in Dinophysis cells in the Gulf of Finland and on PTX-2 in the Baltic Sea. Cellular toxin contents in Dinophysis spp. ranged from 0.2 to 149 pg DTX-1 cell-1 and from 1.6 to 19.9 pg PTX-2 cell-1 in the Gulf of Finland. D. norvegica was found mainly around the thermocline (max. 200 cells L-1), whereas D. acuminata was found in the whole mixed layer (max. 7 280 cells L-1). Toxins in the sediment trap corresponded to 1 % of DTX-1 and 0.01 % PTX-2 of the DSP pool in the suspended matter. This indicates that the majority of the DSP toxins does not enter the benthic community, but is either decomposed in the water column, or transferred to higher trophic levels in the planktonic food chain. We found that nodularin, produced by Nodularia spumigena, was transferred to the copepod Eurytemora affinis through three pathways: by grazing on filaments of small Nodularia, directly from the dissolved pool, and through the microbial food web by copepods grazing on ciliates, dinoflagellates and heterotrophic nanoflagellates. The estimated proportion of the microbial food web in nodularin transfer was 22-45 % and 71-76 % in our two experiments, respectively. This highlights the potential role of the microbial food web in the transfer of toxins in the planktonic food web.

Invertebrate predation and trophic cascades in a pelagic food web : The multiple roles of Chaoborus flavicans (Meigen) in a clay-turbid lake

In lake ecosystems, both fish and invertebrate predators have dramatic effects on their prey communities. Fish predation selects large cladocerans while invertebrate predators prefer prey of smaller size. Since invertebrate predators are the preferred food items for fish, their occurrence at high densities is often connected with the absence or low number of fish. It is generally believed that invertebrate predators can play a significant role only if the density of planktivorous fish is low. However, in eutrophic clay-turbid Lake Hiidenvesi (southern Finland), a dense population of predatory Chaoborus flavicans larvae coexists with an abundant fish population. The population covers the stratifying area of the lake and attains a maximum population density of 23000 ind. m-2. This thesis aims to clarify the effects of Chaoborus flavicans on the zooplankton community and the environmental factors facilitating the coexistence of fish and invertebrate predators. In the stratifying area of Lake Hiidenvesi, the seasonal succession of cladocerans was exceptional. The spring biomass peak of cladocerans was missing and the highest biomass occurred in midsummer. In early summer, the consumption rate by chaoborids clearly exceeded the production rate of cladocerans and each year the biomass peak of cladocerans coincided with the minimum chaoborid density. In contrast, consumption by fish was very low and each study year cladocerans attained maximum biomass simultaneously with the highest consumption by smelt (Osmerus eperlanus). The results indicated that Chaoborus flavicans was the main predator of cladocerans in the stratifying area of Lake Hiidenvesi. The clay turbidity strongly contributed to the coexistence of chaoborids and smelt at high densities. Turbidity exceeding 30 NTU combined with light intensity below 0.1 μE m-2 s-1provides an efficient daytime refuge for chaoborids, but turbidity alone is not an adequate refuge unless combined with low light intensity. In the non-stratifying shallow basins of Lake Hiidenvesi, light intensity exceeds this level during summer days at the bottom of the lake, preventing Chaoborus forming a dense population in the shallow parts of the lake. Chaoborus can be successful particularly in deep, clay-turbid lakes where they can remain high in the water column close to their epilimnetic prey. Suspended clay alters the trophic interactions by weakening the link between fish and Chaoborus, which in turn strengthens the effect of Chaoborus predation on crustacean zooplankton. Since food web management largely relies on manipulations of fish stocks and the cascading effects of such actions, the validity of the method in deep clay-turbid lakes may be questioned.