Väliskeskkonna mõju zoopsammoni koosluste ruumilisele ja ajalisele varieeruvusele

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Psammon on veekogu kaldaäärses niiskes liivas setteosakeste vahelises ruumis elavate mikroskoopiliste organismide kooslus. Psammon pole mitte vaid elurikkuse allikaks, aga neil loomakestel on ka oluline roll veekogude aine- ja energiaringes. Nimelt võib psammoni arvukus tihti ületada veekogude põhjamudas olevate pisiloomade oma. Võrreldes planktoni või bentosega on psammonikooslusi väga vähe uuritud. Käesoleva doktoritöö eesmärkideks oli kirjeldada zoopsammoni koosluste taksonoomilist koosseisu ning domineerimissuhteid ruumis ja ajas. Keriloomad, tsiliaadid, ümarussid, kodaamööbid ja rullikulised olid tüüpilisimad zoopsammoni esindajad, keda leidus kõigis uuritud randades. Kokku leiti töö käigus 159 taksonit, millest 80 taksonit on Eesti faunale uued leiud. Järvedes oli psammonikoosluste taksonirikkus ja arvukus kõrgem kui rannikumeres. Zoopsammoni taksonirikkus oli seotud uuritava ala troofilise tasemega ja muude inimmõjude survega. Zoopsammoni koosluste horisontaalne varieeruvus oli väga suur ning ajas muutuv. Vertikaalne varieeruvus oli suuresti seotud liiva struktuuriga ja tugevalt taksoni-spetsiifiline. Zoopsammoni arvukuse osas ei ilmnenud ühtset sesoonset mustrit, aga taksonirikkus oli suvel suurim. Sesoonsusest enam mõjutas psammoni kooslusi liiva struktuur, toidubaas (orgaanika ja klorofüll a sisaldus liivas, kõrgem taimestik rannas) ja inimtegevus (sh. suvitajate hulk rannas). Seosed keskkonnaparameetrite ja arvukuse vahel olid enamasti taksoni-spetsiifilised ning erinevusi esines isegi ühe perekonna eri liikide vahel. Rannikumere psammonis oli mitmete taksonite arvukus seotud ka liiva kapillaarvee soolsuse ja pH-ga. Käesolev doktoritöö näitas, et näiliselt elutus veekogu kaldaliivas elab väga mitmekesine kooslus, mis võib olla vägagi kõrge arvukusega, hoolimata keskkonnatingimuste suurest varieerumisest. Suur mitmekesisus ja kõrge arvukus viitavad aga psammoni olulisusele veeökosüsteemis.Psammon is diverse group of microscopic organisms living in the interstitial sandy habitat at the water’s edge. Psammon is not only important from the perspective of biodiversity, but may also significantly contribute to the transfer of energy and matter as the populations in beach sand can reach higher densities compared to other benthic habitats. Psammon communities have received very little attention compared to plankton or benthos. The objective of the thesis was to provide an overview of the species composition of zoopsammon communities, their spatial patterns and seasonal dynamics in relation to environmental parameters. The most common taxa that were found from all studied beaches were nematodes, rotifers, ciliates, testate amoebae and harpacticoids. A total of 159 taxa were determined, of which 80 taxa were new records for Estonia. The taxonomic richness and total zoopsammon abundance was much higher in lake beaches than in coastal beaches. Taxonomic richness was related to trophic state of and anthropogenic impact on the sampling site. The horizontal pattern is highly variable and poorly predictable. The vertical distribution was taxon-specific and depended on the sediment type. There was no clear seasonal pattern for the overall psammon abundance, however most taxon-rich season was summer. Sand structure, feeding conditions (sand organic matter and chlorophyll a content, vegetation cover at a transect) and human activities (e.g. trampling by swimmers) proved to be more important variables structuring the psammon communities than seasonality. The majority of psammon taxa had taxon-specific responses to their environment and differences occurred even within one genus. In coastal beaches the abundance of many taxa was related also with porewater pH and salinity. This thesis showed that the seemingly deserted beach habitat hosts a diverse community which can reach high population density, despite the unstable and very fluctuating environment in the habitat. The high abundance and taxonomic richness indicate the importance of psammon communities in the water ecosystem

Seasonal variability in the structure and functional diversity of psammic rotifer communities: role of environmental parameters

Data on the variability in structure and functioning of interstitial rotifer assemblages are rare; however, this knowledge is essential for understanding their role in the interstitial food web. In the present study, we characterized psammic rotifer communities in terms of dominance structure, trophic traits, taxonomic and functional diversity at a seasonal scale in freshwater lakes across Estonia and coastal beaches of the Baltic Sea. A total of 42 rotifer species were found from the coastal beaches and 66 species from the lakes. Functional indices did not exhibit smaller seasonal variability and neither did they respond better to changes in the environment compared to taxonomic indices. However, there were differences how environmental variables affected these two broad groups of response variables. The taxonomy-based indices of rotifer communities were primarily driven by seasonal temperature regime, sediment characteristics and anthropogenic stressors, whereas the trait-based indices were a function of ecosystem types (freshwater or brackish water). The functional indices of the psammic rotifer communities strongly distinguished between freshwater and brackish habitats indicating that rotifers have different functional roles in food webs in fresh and brackish water environments

Introduction of a functionally novel consumer to a low diversity system: Effects of the mud crab Rhithropanopeus harrisii on meiobenthos

The Harris mud crab Rhithropanopeus harrisii recently expanded into much of the Baltic Sea. This invasion is expected to have significant effects on the structure and functioning of benthic ecosystems due to the lack of native crabs. Habitat type potentially modulates the effects as crabs are expected to behave differently in different habitats. In this study we experimentally evaluated the effect of R. harrisii on the species composition and dominance structure of shallow water meiobenthos within common habitat types of the north-eastern Baltic Sea. Among the studied environmental variables R. harrisii had by far the strongest effects on meiobenthos. The effects of R. harrisii varied among different habitats with the crab mostly modifying taxonomic composition and species abundances of meiobenthic communities on unvegetated soft bottom sediments. Our experiment also showed that boulders provided shelter for R. harrisii and thereby reduced their burrowing activity and effects on the adjacent soft bottom meiobenthos