Browsing by Subject "Akvaattiset tieteet"

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  • Tolvanen, Oula (Helsingfors universitet, 2015)
    Tutkielman tavoitteena oli laatia todennäköisyyspohjainen kanta-arviomalli merivaelteisen taimenen (Salmo trutta L.) juveniili vaiheen populaatiodynamiikan kuvaamiseksi. Mallin tarkoituksena on kuvata taimenen jokipoikasvaihe kuoriutumisesta merivaellukselle lähtöön tai sukukypsyyteen saakka, tiivistämällä saatavilla oleva tieto taimenen ekologiasta populaatioparametreiksi. Näitä parametreja olivat ikäryhmäkohtainen selviytymisen todennäköisyys ja ikäryhmäkohtainen syönnösvaellukselle lähdön todennäköisyys. Epävarmuuden huomioimiseksi mallin parametrien kuvaamiseen käytettiin todennäköisyysjakaumia. Ikäryhmäkohtainen syönnösvaellukselle lähdön todennäköisyys kuvattiin käyttämällä käyräfunktiota, jonka parametrit liitettiin aikaisemmin julkaistuihin aineistoihin taimenen keskimääräisen vaellusiän vaihtelusta leveyspiirin mukaan. Mallin muiden parametrien odotusarvojen asettaminen ja mallin rakenteen laatiminen perustui asiantuntija-arvioihin ja aikaisemmin julkaistuun taimenta tai sen sukulaislajeja koskevaan tutkimustietoon. Mallissa käytettyjen parametrien posteriorijakaumat ratkaistiin käyttämällä Markov chain Monte Carlo (MCMC) -simulointia. MCMC-simuloinnin toimivuus tarkastettiin käyttämällä keinotekoisesti tuotettua havaintoaineistoa. Mallin yhteensopivuutta todellisiin havaintoaineistoihin tutkittiin sovittamalla malli kahdesta Suomenlahteen laskevasta joesta kerättyyn sähkökoekalastus ja vaelluspoikaspyyntiaineistoon. Viron puoleisen Pirita joen aineisto koostui vuosien 2005 - 2013 sähkökoekalastusaineistosta ja vuosien 2006 - 2014 vaelluspoikaspyyntiaineistosta. Suomen puoleisen Ingarskilan joen aineisto koostui vuosien 2009 - 2013 sähkökoekalastusaineistosta ja vuosien 2012 ja 2013 vaelluspoikaspyyntiaineistosta. Molempien jokien aineistojen, sekä kirjallisuudesta kerätyn 41 muun joen vaelluspoikasten keskimääräisistä i'istä koostuva aineiston analysointi toteutettiin samanaikaisesti hierarkkisena meta-analyysina. Mallin sovituksen yhteydessä havaittiin, että malli systemaattisesti yliarvioi keväisin tutkimusjoista alasvaeltavien taimenen poikasten määrän. Mallin havaittiin kuitenkin ennustavan onnistuneesti analyysistä poisjätetyn Piritajoen vuoden 2014 vaelluspoikaspyyntiaineiston ikäjakauman. Kirjallisuudesta kerätyn aineiston pohjalta taimenten syönnösvaellukselle lähtemisen todennäköisyyttä kuvaavan käyrän µ parametrin havaittiin korreloivan positiivisesti leveyspiirin kanssa. Kirjallisuuskatsauksen perusteella tämä työ on ensimmäinen yritys laatia todennäköisyyspohjainen populaatiodynamiikkaan perustuva kanta-arviomalli, joka pystyy huomioimaan myös taimen populaatioiden vaelluskäyttäytymisen. Mallin laajamittainen käyttö kalastuksen säätelyn tukemisessa vaatii vielä parannuksia mallin rakenteisiin.
  • Sairanen, Eeva Elisa (Helsingfors universitet, 2015)
    Sound travels faster and further in water than in air while electromagnetic radiation, among it visible light, attenuates fast. Marine animals have adapted to use sound in foraging, predator avoidance, orientation and communication with conspecifics. The underwater soundscape of the Baltic Sea remains largely undiscovered. The area is a unique acoustic environment due to its variant hydrography, broken coastline, shallowness, low salinity and the resulting strong stratifications. The harbor porpoise (Phocoena phocoena) is the only cetacean inhabiting the area, and its Baltic Sea subpopulation is critically endangered. This work is based on first sound pressure measurements of BIAS (Baltic Sea Information on the Acoustic Soundscape) -project by Finnish Environment Institute and other project participants. Measured sound pressure levels are compared to weather and shipping observations to collect information about the contributions of natural and anthropogenic sound sources to underwater sound pressure levels in the Baltic Sea. In addition porpoise observations collected at the Universities of Southern Denmark and Århus are compared to measured sound pressure levels and shipping data to examine if increased noise levels or increased shipping activity have an impact on harbor porpoise echolocation activity. The results show that at the Gulf of Finland both weather and shipping drive the levels of ambient noise at low frequencies (63 and 125 Hz third-octave bands). However the sound pressure levels caused by ships near the stations (up to 5 km) always exceeded all natural variation. Increased sound pressure levels and ship proximity seemed to have an impact on porpoise activity at the area. When a ship was very close (2 km), the registrations of porpoise echolocation clicks decreased with decreasing proximity to ship. On the other hand during spring months an increase in porpoise echolocation was recorded in relation to increased sound pressure levels, which might indicate the porpoises compensating to increased background noise by echolocating more frequently or loudly.
  • Joensuu, Laura (Helsingfors universitet, 2010)
    Carbon dioxide (CO2) is the most significant greenhouse gas produced by mankind. The oceans play a significant role in the global carbon cycle. Due to its restricted size the Baltic Sea doesn't play an important role as a global reservoir. However, due to its large annual fluctuations, alternations in salinity in the different basins, and a wide drainage-basin with varying soil, it is an excellent study system. The aim of this research was to examine both the vertical and the horizontal distributions of the components of the inorganic carbon in the Baltic Sea, their interactions and annual fluctuations. In addition, the long-term alterations of the surface water pH were reviewed. The study was performed at the Finnish Meteorological Institute as a part of an international research programme regarding the Baltic Sea (BONUS: Baltic-C). The total alkalinity in the Baltic Sea was found to be determined mainly by salinity. Surface water alkalinity is controlled by mixing of highly saline waters originating in the North Sea and waters of low salinity from the rivers draining into the Baltic Sea. The amount of total alkalinity entering the Baltic Sea through the rivers is dependent on the soil quality in the catchment area. According to the alkalinity-salinity-relation, the Baltic Sea can be divided into four distinguishable basins. The alkalinity is lowest in the Bothnian Bay and grows towards the Kattegat as a function of salinity. Salinity controls alkalinity, which together with biological activity controls the concentration of total inorganic carbon. The distribution of total inorganic carbon is very similar to that of total alkalinity. The results in this study support earlier findings on total inorganic carbon and total alkalinity in the Baltic Sea. As the atmospheric partial pressure of carbon dioxide (pCO2) rises, the partial pressure in the surface waters rises as well. In addition to the concentration of total inorganic carbon, the biological activity has a great impact on the annual fluctuations of pCO2. The primary production forms the basis of the biological uptake of carbon dioxide in the surface waters. The results indicate that the Baltic Sea fluctuates from being a source to being a sink for atmospheric CO2 according to the annual fluctuations in primary production. However, simultaneous measurements on the atmospheric pCO2 are needed to ascertain the assumptions on the direction of CO2 flux between the sea and the atmosphere. The rise of the pCO2 in water leads to descending pH levels, because of a relative shift in the components of total inorganic carbon. The results indicate a slight decreasing trend in pH levels In the Baltic Sea during the 30-year observation period, however more research on the subject is needed. The reliability of pCO2-values calculated from known parameters was estimated by comparing them to the measured values. The study shows that pCO2 results for the Baltic Sea derived from the program developed for the oceans, should be used with caution.
  • Salonen, Iines (Helsingin yliopisto, 2020)
    The marine benthic ecosystem, encompassing the sea floor and the sedimentary habitats within, plays a crucial role in major biogeochemical cycles and the functioning of the marine ecosystem. Despite its importance, many aspects of its ecology remain understudied, such as microbial community composition and bacteria–eukaryote interactions. In recent years, molecular ecology methods, in particular DNA metabarcoding, have provided us with new insights into benthic ecology. Compared with traditional methods, metabarcoding has the advantage of being applicable to various samples, generating large data sets and allowing reliable taxonomic identification without requiring morphological identification. This thesis explores the use of the DNA metabarcoding method in examining the benthic ecosystem from different angles and targeting both eukaryote and prokaryote communities. 18S rDNA metabarcoding was used to target and track temporal variation in eukaryote communities in coastal sediment of the northern Gulf of Finland. The results demonstrate that DNA metabarcoding can be used to study sediment eukaryote community composition and variation over time. The key factor shaping the sediment eukaryote community was time, firstly the year and then the season, whereas location played a smaller role in explaining the community variation. In addition, the changes in the community composition could be linked to larger environmental phenomena, such as the timing and duration of the ice season, which in turn influenced the phytoplankton bloom. The ability of DNA metabarcoding surveys to resolve sediment community response to environmental factors indicates a potential for applications in biomonitoring and environmental assessment. Nevertheless, some limitations remain, such as the lack of standardization in metabarcoding methods and data analysis, and deficiencies in the reference databases. In addition, 18S and 16S rDNA metabarcoding were employed to resolve trophic strategies and microbial interactions of a common benthic unicellular eukaryote, the foraminifera. Samples for these studies were collected from the intertidal mudflats of Texel Island in the Netherlands. Both intracellular bacteria and eukaryotes of foraminifera were targeted in these studies, as well as the foraminifera’s own DNA, which allowed reliable genus-level identification. The intracellular eukaryote operational taxonomic units (OTUs) of different foraminiferal species reflected their trophic preferences: Haynesina sp. (genotype S16) and Elphidium sp. (genotype S5), which are likely to prefer an algal diet and/or are known to have a tendency for kleptoplasty, had an intracellular eukaryote content dominated by diatoms. In contrast, Ammonia sp. (genotype T6) contained also metazoan OTUs, implying potential predatory behaviour in addition to an algal diet. Based on these results, DNA metabarcoding can provide a comprehensive tool for the investigation of life strategies and ecology of even unicellular organisms, such as the foraminifera. The intracellular bacterial OTUs of all foraminiferal species were enriched in sulphur-oxidizing and sulphate-reducing bacteria compared with the surrounding sediment bacterial community, where the relative abundancies of these bacteria were lower. The intracellular bacterial 16S OTUs of foraminifera were found to be species-specific, and the phylogenetic analysis of the sulphur-cycle related aprA OTUs showed that some of these intracellular bacteria were closely related to known endobionts of other organisms. Therefore, the results suggest that intertidal benthic foraminifera may have a previously overlooked role in the benthic sulphur cycle. Further research is needed to understand the exact role of the sulphur-cycle associated bacteria in foraminiferal ecology. For example, looking into the environmental conditions under which transcription of the sulphur-cycle genes takes place would enable assessment of their role and the potential foraminifera/endobiont contribution to the benthic sulphur cycle.
  • Jaale, Marko (Helsingfors universitet, 2007)
    Saaristomeren pinnanalaisen ravintoverkon rakennetta sekä ravinteiden alkuperää ja kulkeutumista tutkittiin hiilen ja typen pysyviä isotooppeja hyväksi käyttäen. Tutkimuksen kohteena olivat suspendoitunut partikkeliaines (SPM), sedimentin pintakerros, pohjaeläimet, kalat ja makrolevät. Näytteitä otettiin toukokuussa, kesäkuussa ja lokakuussa. Ravinnelähteiden arvioinnin ohella tutkittiin voiko sisäsaariston kalankasvatuksen vaikutusta määritellä analysoimalla kalanrehupellettejä. Lisäksi arvioitiin joidenkin lajikohtaisten tai lajien välisten ominaisuuksien erojen vaikutusta (esimerkiksi eläimen koko ja kudosten C:N –suhde rasvapitoisuuden kuvaajana) δ-arvojen määräytymiseen. Myös joitain tarkennuksia tehtiin lajien ravinnonkäyttöluokituksiin. Sisäsaaristossa toukokuussa pian lumien sulamisen aiheuttaman kasvaneen jokivirtaaman jälkeen SPM:stä havaittiin korkeita δ13C- ja δ15N-arvoja (keskimäärin -16 ‰ ja 9 ‰, vastaavasti). Ulkosaariston asemilta saatiin paljon alempia arvoja (-24 ‰ ja 4 ‰, vastaavasti). Sisäsaaristossakin arvot laskivat kesäkuuhun mennessä (-26 ‰ ja 5 ‰, vastaavasti) ollen kuitenkin hieman korkeampia kuin samaan aikaan tutkituilla ulommilla välisaariston asemilla. Kasviplanktonin lajistokoostumusta tutkittiin touko- ja kesäkuussa, mutta suuria eroja ei ajankohtien välillä havaittu. Lokakuussa sateisen loppukesän jälkeen δ13C oli tasainen (-23 ‰ - -24 ‰) koko tutkimusalueella, mutta δ15N oli taas huomattavasti korkeampi sisäsaaristossa (8 ‰) kuin ulkosaaristossa (4 ‰). Päinvastoin kuin yleensä tutkimuksissa on esitetty, tässä tutkimuksessa korkeat δ13C ja/tai δ15N-arvot kuvannevat lisääntynyttä jokien tuomaa terrestristä alkuperää olevaa ravinnekuormaa. Lisäksi kauden aikana suuresti vaihtelevat, mutta silti voimakkaasti korreloivat δ13C ja δ15N indikoivat hiilen ja typen olevan pääosin samaista alkuperää. Kirjallisuudessa ravinnepulssien yhtäaikaisesti korkeat δ13C ja δ15N katsotaan alkuperältään ihmis- tai eläinperäisiksi ja yleensä liitetään karjanlannan käyttöön lannoitteena. Tätä ei kuitenkaan voitu Saaristomerellä osoittaa, koska terrestrisiä ravinnelähteitä ei tutkittu. Kuitenkin muista tunnetuista SPM:n δ-arvoja voimakkaasti muokkaavista tekijöistä voitiin poissulkea ravinnerajoitteisuudesta johtuva fraktionaation muutos sekä synteettisten lannoitteiden käyttö ja kalankasvatus ravinnelähteinä. Pintasedimentistä saatiin paljon tasaisempia δ13C- ja δ15N-arvoja kaikilla näytteenotoilla (keskimäärin -24 ‰ ja 4 ‰, vastaavasti), jotka kuvannevat sedimentoituvan aineksen pitkäaikaisia keskiarvoja. Havaittavissa oli hienoinen laskeva suuntaus kohti ulompia asemia ja monista pohjan lähellä tai sedimentissä elävistä eläimistä saatiin samaan tapaan laskevia arvoja. SPM:n vaihtelevat ja eläinten δ-arvot korreloivat heikosti lukuunottamatta joitakin suspensionsyöjiä (Balanus improvisus ja Mytilus edulis). δ13C ja C:N korreloivat negatiivisesti joillakin lajeilla (Macoma balthica, Monoporeia affinis ja Mytilus edulis), joka johtunee muuttuvasta rasvojen osuudesta kudoksissa. Ainakin näiden lajien käyttöön ravinnelähteiden arvioinnissa kannattaa suhtautua varauksella. Makrolevien δ15N oli n. 4 ‰ korkeampi sisäsaaristossa kuin ulommilla asemilla, joka myöskin heijastanee jokien tuoman terrestristä alkuperää olevien ravinteiden vaikutusta. Fucus vesiculosus, tutkimuksen ainut varsinainen monivuotinen levä, sai 6 ‰ korkeampia δ13C-arvoja kuin muut levät keskimäärin. Gammarus sp:n Idothea baltican δ15N seurasi makrolevien δ15N:n vaihtelua, mutta δ13C:n perusteella arvioituna ne suosivat rehevöitymisen seurauksena runsastuvia rihmaleviä sisäsaaristossa, kun taas F. vesiculosus näytti kasvattavan tärkeyttä ravintona ulkosaaristossa. Hiilen ja typen pysyvät isotoopit osoittautuivat tehokkaiksi työkaluiksi ravinteiden lähteiden ja kulkeutumisen tarkasteluissa erityisesti sisäsaaristossa, vaikkakin joitakin lajikohtaisia piirteitä on otettava huomioon ja joidenkin biologisten prosessien, kuten denitrifikaation osuus fraktionaation aiheuttajana pitäisi määrittää ennen kuin luotettavia arvioita ravinnelähteistä voidaan tehdä.
  • Saulamo, Kari (Helsingin yliopisto, 2018)
    Fisheries management needs to address an array issues to achieve long-term sustainability. Economically viable fisheries require healthy fish stocks. Our knowledge of fish populations is still limited, as fish cannot be observed directly and they are typically highly mobile. Fish populations also fluctuate temporally and spatially depending on the biophysical characteristics of the environment and interactions in the ecosystem. By increasing our knowledge of the ecology of exploited species and how they respond to the impacts of fishing, we increase the probability of success with the management of the fish populations. The main contribution of this thesis is improved scientific understanding of the biology of the pikeperch and how this relates to the management of fisheries. In the thesis, the movements of the pikeperch are studied during the spawning season to gather information on biological characteristics, such as changes in size distribution, sex ratio and maturity between fish ascending to the spawning grounds at different times. The interaction between biology and the management of the pikeperch is studied by analysing the situation in where pikeperch are exploited by several management units. The effects of high fishing pressure and selective fishing on growth and the production of pikeperch stock are also studied. It is demonstrated that there are differences in the biological characteristics between pikeperch arriving at the spawning ground at different times, and signs that there can be early and late spawners in the populations. It is also shown that in cases where the pikeperch migrates over several management areas, overfishing is inevitable if there is no agreed cooperation between the areas. It is proven that excessive fishing pressure with highly selective fishing gears creates strong phenotypic selection for slower growth in the studied pikeperch population. Fisheries managers are advised to consider the spatial and temporal dynamics of the pikeperch stocks in order to protect the different stock components. Pikeperch managers should focus on distributing harvesting with caution regarding space, time and also between age groups to avoid adverse ecological effects from fishing, and to avoid the risk of decreasing the long-term productivity of the stock.
  • Kauko, Hanna (Helsingfors universitet, 2013)
    The bioluminescent and toxin-producing dinoflagellate Alexandrium ostenfeldii forms dense blooms in coastal areas of the Baltic Sea. Bioluminescence, light production by an organism through a chemical reaction, is a nocturnal, rhythmic phenomenon in surface algae. In this study, the bioluminescence pattern and rhythm of A. ostenfeldii was under investigation. Procedures for continuous bioluminescence measurements, to support dedicated environmental monitoring of toxic dinoflagellate blooms, were developed. The study consisted mainly of laboratory experiments. Semi-continuous field measurements were included for comparison. In the laboratory, the light production of monocultures of A. ostenfeldii was measured with a spectroluminometer or bathyphotometer, continuously during the night, or for several consecutive days. The method to stimulate bioluminescence was varied, as well as the recovery period of the cells after stimulation. Light regimes during growth and pre-measurement adaptation were also taken into account. The experiments confirm that bioluminescence in A. ostenfeldii follows a circadian pattern and can be stimulated with the chosen methods. Bioluminescence could also be stimulated after culturing in continuous light. Measurement parameters for rhythm experiments (stimulation frequency and recovery period), were optimised. Multi-day experiments in complete darkness suggested that sufficient energy was available to maintain bioluminescent response during one night, although an endogenous rhythm remained present. These experiments gave insight to the phenomenon of bioluminescence regulation in A. ostenfeldii, but also gave rise to new questions. Some repeated measurements resulted in very low bioluminescence intensity, without an obvious reason. The light regime is not the only factor controlling bioluminescence. The interplay between bioluminescence and the growth and condition of the cultures is of interest.
  • Jernström, Janni (Helsingfors universitet, 2015)
    The chemical composition of macroalgae varies between species, habitat and environmental conditions. The lipid content of macroalgae changes between seasons and different environmental factors such as light, nutrient levels and temperature. The lipid levels are higher during winter and spring than in the summer. Macroalgae from the cold water are richer in polyunsaturated fatty acids (PUFAs) than macroalgae from the warm waters. Nutrient limitation increases the synthesis of lipids in macroalgae. Studies show also that brown macroalgae (Phaeophyceae) have higher lipid content than green (Chlorophyta) and red (Rhodophyta) macroalgae. Macroalgae produce neutral lipids mainly triacylglycerols (TAGs) under stress condition so they shift from membrane lipid synthesis to storage lipid synthesis. The content of triacylglycerols in macroalgae is of interest because triacylglycerols can be used as bases of biodiesel. In the experiment we wanted to define the application of Baltic Sea macroalgae as raw material for biodiesel. We also studied how the different levels of nutrients affect the content of total lipids and fatty acid composition in the studied macroalgae. The hypothesis was that the studied macroalgae would produce more lipids in nutrient limited conditions than in nutrient replete conditions. At the same time, the differences between the content of lipids between macroalgae species was examined. Two green macroalgae and one red macroalgae species were used in the experiment (Ulva intestinalis, Cladophora glomerata and Ceramium tenuicorne) to study the total lipid content and the fatty acid composition of the macroalgae. The macroalgae species were selected because they are typical macroalgae species in the Baltic Sea's littoral zone. The experiment was conducted as a factor experiment for 10 days in August and October in the Tvärminne Zoological Station. The experiments nutrient treatments were designed as to study the effect of nitrogen and phosphorus separately and together on macroalgae lipid content. The macroalgae lipids were extracted with chloroform:methanol (2:1 -vol/vol) mixture. The macroalgae lipids and the fatty acid composition were studied with gas chromatography-mass spectrometry (GC-MS) from extracted and esterified fatty acid methyl esters (FAMEs). We also fractionated the neutral lipids from the total lipids to quantify the amount of neutral lipids. The total lipid content of the studied macroalgae species varied between specie but not between nutrient treatments. The total lipids contents ranged from 31 to 193 mg l-1, with the lowest total lipid content found in U. intestinalis in the October experiment. The total lipid content of the macroalgae accounted only 2% of the macroalgae species dry weight. The total fatty acid content of the studied macroalgae species ranged from 0,7 to 9,0 mg l-1with the highest values found in C. glomerata and the lowest in U. intestinalis in the October experiment. The total fatty acid content differed between species but not between nutrient treatments. The fatty acid composition of the macroalgae varied slightly but there were similarities between the fatty acid compositions between the studied species. The saturated fatty acid contents were the highest among the studied macroalgae (42,0-49,7%). U. intestinalis in the August and October experiment contained more polyunsaturated fatty acids (PUFAs) (45,1%; 46,9%) than C. glomerata (23,2%) and C. tenuicorne (22,8%). The major fatty acid was the palmitic acid (C16:0) in all the studied macroalgae species (32,3-45,7% of total fatty acids). The neutral lipid amount from U. intestinalis differed between August and October specimens but didn't differ between nutrient treatments. The neutral lipid content ranged from 0,6 to 4,2 mg l-1 with the lowest amounts found in U. intestinalis from Octobers experiment. The fatty acid composition of the neutral lipids in U. intestinalis resembled one another. The total lipid content of the studied macroalgae was different from results of other studies made by macroalgae because the sampling location and the season affects the total lipid content of macroalgae. The low amounts of total lipids and fatty acids in U. intestinalis in October can be explained by the fact, that U. intestinalis was not healthy at the time of the experiment. Comparing the total lipid contents of the macroalgae is therefore difficult because of the rundown nature of the U. intestinalis in October. The studied macroalgae didn't contain the highest amounts of lipids in the nutrient deprived conditions because the macroalgae experienced shortage of nitrogen for example in the control and added phosphorus treatments. The macroalgae should have been given the opportunity to adjust to the new conditions before the experiment. The different water temperature between the August and October experiment could account more of the differences between the total lipid content of the macroalgae than the nutrient treatments. The fatty acid composition of the macroalgae was similar to those reported from other studied. The low amount of fatty acids supports the findings of the studies because typically most lipids are bound to membranes such as glycolipids and phospholipids. On the other hand, the high saturated fatty acid content reveals that the macroalgae were in stress conditions. The macroalgae are suited as raw material for biodiesel because of the high total lipid and saturated fatty acid content of the macroalgae species. The macroalgae could be grown to produce more lipids in nutrient deprived than in nutrient saturated conditions by choosing the suited macroalgae and the optimal sampling season. The total lipid content of macroalgae can be enhanced with two-stage nitrogen supply growth strategy which has been demonstrated in the microalgae Chlorella vulgaris. In the first stage the macroalgae could be grown in nitrogen replete conditions to optimize biomass productivity. In the second stage the macroalgae would be grown in nitrogen limited conditions to increase lipid content.
  • Siitonen, Susanna (Helsingfors universitet, 2005)
    In this thesis I used paleolimnological methods to study changes in two lakes in Kilpisjärvi region, Somas and Vallijärvi, during the last c. 400 years. I examined the remains of cladocera preserved in sediments to find out species composition and population size in the past. The objective of this study is to reveal if the cladoceran species compositions have changed in the lakes and what is has been driving these changes. In addition, I will use cladoceran resting eggs from the sediment of lake Somas to examine the applicability of resting eggs as a new paleolimnological method. In April 2002 I cored sediment sequences from the lakes and sliced them into 0,5-1 cm subsamples. The samples were dated with led isotope, 210Pb, to reveal the sedimentation rate. From the sediments I determined the organic carbon content, counted the proportions of different cladoceran species, the absolute numbers of individuals and the yearly accumulation of cladocera to the sediment. In addition I calculated the relative share of resting eggs. I examined relationships between the samples and between the samples and measured environmental variables with a set of multivariate methods (DCA, DCCA, PCA, RDA). I tested a previously created cladoceran-water depth model to Vallijärvi data in order to reconstruct past water level development in the lake. In the turn of the last century a distinct interface between two different species compositions can be seen in both lakes. Also the accumulation of cladocera into the sediments has increased in both lakes, and the planktic species have out paced the littoral ones during the last century indicating an increase in productivity. Also sedimentological processes have develop similarly in the lakes. Due to the location of the lakes, their differing morphology and history the changes in biological and sedimentological processes have been stronger in the lake Vallijärvi. The model on past water levels seemed to perform well in the lake Vallijärvi. Water level reconstruction was not, however, problem free, as similar development in species composition could be a consequence of increase in productivity. The amounts of resting eggs seemed to follow negatively the air temperatures of the open water period. However, before the resting egg method can be applied as a paleolimnological indicator, a more extensive data set on the relationship between resting eggs and temperatures is required.