Ecological relations of cladocerans in a brackish-water ecosystem
Date
2010-08-11
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Abstract
Merelised vesikirbulised moodustavad olulise osa Läänemere mesozooplanktoni arvukusest ja biomassist suvel. Tänu partenogeneesile (neitsisigimine) on vesikirbulised võimelised saavutama soodsates keskkonnatingimustes kiiresti suure arvukuse, mis annab neile eelise kohanemiseks kiiresti muutuvates keskkonnatingimustes. Massilise arengu ajal on vesikirbulised oluliseks toiduks kaladele ja röövtoidulistele selgrootutele. Kliimamuutuste ja eutrofeerumise kõrval on üheks oluliseks planktonikoosluste struktuuri ja dünaamikat mõjutavaks teguriks ka võõrliikide invasioon kusjuures just tulnukvesikirbulised on seni olnud Läänemere ökoüsteemis olulisemad planktilised võõrliigid. Käesoleva doktoritöö eesmärgiks on selgitada Läänemere vesikirbuliste koosluses liigilisel tasandil toimunud ajalis-ruumilisi muutusi sõltuvalt keskkonnatingimuste varieeruvusest, mis on põhjustatud nii looduslikest (kliima) kui ka inimtekkelistest (eutrofeerumine, võõrliikide invasioon) teguritest ja protsessidest. Kõige arvukamateks vesikirbulisteks olid Bosmina spp., Pleopis polyphemoides ja Evadne nordmanni. Viimastel aastakümnetel on lisandunud tulnukliikidena Ponto-Kaspia päritolu vesikirbulised Cercopagis pengoi ja E. anonyx. Vesikirbuliste arvukuse muutused ligi poole sajandi pikkusel ajaskaalal on mõjutatud mitmete tegurite, nagu kliima, eutrofeerumise ja bioinvasioonid, koosmõjust, kusjuures eraldi võttes selgitavad kliimatingimused arvukuse muutlikkust paremini kui eutrofeerumine. Ilmselt toiduahela suhete tõttu (kisklus) on röövtoidulise võõrvesikirbulise C. pengoi invasioon põhjustanud varemesinenud seose katkemise kohalike domineerivate väikesemõõduliste vesikirbuliste ja elutakeskkonna vahel. Antud tulemused täiendavad oluliselt meie teadmisi sellest, milliseid muutusi, mis mahus ja milliste protsesside tõttu võib inimtegevusest põhjustatud võõrliikide invasioon põhjustada mereökosüsteemides. Suurimad aastatevahelised muutused pelaagiliste kalade toidubaasis olid seotud nende olulise toiduobjekti Bosmina arvukuse dünaamikaga, kuid arvukuse varieeruvus ei osutunud siiski piisavaks, et põhjustada püsivaid muutusi kalade toitumisaktiivsuses ning tarbitud zooplanktoni kogustes.
Marine cladocerans may form a significant fraction of summer zooplanktonic communities in the Baltic Sea. Cladocerans possess an ability to increase their abundance (by using parthe-nogenetic reproduction mode) if the environment is favourable. This ability is very characteristic for marine cladocerans and makes them especially adapted to opportunistic utilisation of seasonally changing resources. At high densities, cladocerans are important food resource for various planktivorous fishes and invertebrate predators. Together with climate change and eutrophication, invasion of alien species has been one of the factors altering the structure and dynamics of plankton communities, whereas the most important planktic alien species in the Baltic Sea ecosystem have been alien cladocerans. The general task of the present thesis was to identify naturally and anthro¬pogenically induced species-level changes in the cladoceran community of the temperate brackish-water Baltic Sea at different spatio-temporal scales. The dominating taxa were Bosmina spp., Pleopis polyphemoides and Evadne nordmanni. During the last decades, invasions of two additional cladoceran species, Cercopagis pengoi and Evadne anonyx, both of Ponto-Caspian origin, have been recorded. Climate, eutrophication and bioinvasions interactively affected cladoceran abundance at multi-annual scale during a half of the century with climate being better descriptor than eutrophication. In addition, human-mediated invasion of the predatory cladoceran C. pengoi has resulted in a disruption of the previously existing ecological relations of the dominating native small-sized cladoceran species. However, these alterations have been insufficient to cause additional significant shifts in population abundance, but sufficient to hamper recoveries from losses through direct predation. These results contribute to a substantially advanced understanding on how human-mediated invasion of alien species may interact with climate-driven changes in marine ecosystems, providing also additional evidence on the magnitudes of these changes. Major annual-scale variation in the important prey of the pelagic fish species was associated with the dynamics of Bosmina. However, the observed annual-scale variation in cladoceran abundance and biomass did not to initiate any consistent alterations in fish feeding activity and, therefore, also in the total amounts of zooplankton consumed.
Marine cladocerans may form a significant fraction of summer zooplanktonic communities in the Baltic Sea. Cladocerans possess an ability to increase their abundance (by using parthe-nogenetic reproduction mode) if the environment is favourable. This ability is very characteristic for marine cladocerans and makes them especially adapted to opportunistic utilisation of seasonally changing resources. At high densities, cladocerans are important food resource for various planktivorous fishes and invertebrate predators. Together with climate change and eutrophication, invasion of alien species has been one of the factors altering the structure and dynamics of plankton communities, whereas the most important planktic alien species in the Baltic Sea ecosystem have been alien cladocerans. The general task of the present thesis was to identify naturally and anthro¬pogenically induced species-level changes in the cladoceran community of the temperate brackish-water Baltic Sea at different spatio-temporal scales. The dominating taxa were Bosmina spp., Pleopis polyphemoides and Evadne nordmanni. During the last decades, invasions of two additional cladoceran species, Cercopagis pengoi and Evadne anonyx, both of Ponto-Caspian origin, have been recorded. Climate, eutrophication and bioinvasions interactively affected cladoceran abundance at multi-annual scale during a half of the century with climate being better descriptor than eutrophication. In addition, human-mediated invasion of the predatory cladoceran C. pengoi has resulted in a disruption of the previously existing ecological relations of the dominating native small-sized cladoceran species. However, these alterations have been insufficient to cause additional significant shifts in population abundance, but sufficient to hamper recoveries from losses through direct predation. These results contribute to a substantially advanced understanding on how human-mediated invasion of alien species may interact with climate-driven changes in marine ecosystems, providing also additional evidence on the magnitudes of these changes. Major annual-scale variation in the important prey of the pelagic fish species was associated with the dynamics of Bosmina. However, the observed annual-scale variation in cladoceran abundance and biomass did not to initiate any consistent alterations in fish feeding activity and, therefore, also in the total amounts of zooplankton consumed.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
doktoritööd, ökoloogia, bioloogia