Kliimasoojenemise mõju zoo- ja fütoplanktoni suhetele parasvöötme järvedes

Antud töö eesmärgiks oli kirjanduse abil selgitada veekogude soojenemisest tingitud potentsiaalseid mõjusid zoo- ja fütoplanktoni dünaamikale ning nendevahelisele toitumissuhetele. Kontrolliti hüpoteesi, mille kohaselt nõrgeneb kliimasoojenemise käigus zooplanktoni võime kontrollida fütoplanktoni arengut sesoonse dünaamika muutuste kaudu. Kliimauuringute tulemuste põhjal on ennustatud temperatuuri tõusu globaalsel tasandil. Kirjanduse analüüsi tulemusena võib välja tuua järgmised põhilised nähtused ja seosed, mis tõenäoliselt leiavad aset soojeneva kliima tulemusena zoo- ja fütoplanktoni dünaamikas ning toitumissuhetes: · Kõrgenenud veetemperatuuri tingimustes leiavad fütoplanktoni kevadised biomasside maksimumid aset varem ja zooplanktoni kevadised biomasside haripunktid hiljem, tuues kaasa zoo- ja fütoplanktoni biomasside mitteajastumise ning toitumisseoste nõrgenemise, mille tulemusel võib selgevee faas planktoni fenoloogiliste sündmuste reas ära jääda; · Temperatuuritõus mõjutab soojalembeste sinivetikate arengut, tuues kaasa järkjärgulise sinivetikate osakaalu suurenemise fütoplanktoni kooslustes ning sellega suureneb ka risk potentsiaalselt mürgiste sinivetikate sesoonseks massiliseks vohamiseks, mis põhjustavad häireid toiduahelate funktsioneerimises; · Kõrgemal temperatuuril intensiivistub füto- ja zooplanktoni parasiitide elutegevus, millel on koosluste arvukusi piirav ning liikide vahetumist esilekutsuv mõju; · Muutused toiduahela ülemistel astmetel avalduvad kaskaadmõjudena planktonikoosluste tasemetel – omnivoorsete kalade osakaalu suurenemine ning omnivoorse toitumisviisi prevaleerimine põhjustab zooplanktoni kooslustes väiksema kehasuurusega liikide domineerimist. Suuremate herbivoorsete zooplankterite osakaalu vähenemine mõjutab juba otseselt zooplanktoni võimet fütoplanktoni kasvu kontrollida. Eelnevast järeldub, et tulenevalt kliimasoojenemisest tingitud muutustest zooplanktoni koosseisus ja dünaamikas, kontrollib zooplankton fütoplanktonit tõenäoliselt vähem ja see kinnitab eelpool püstitatud hüpoteesi.

Using various sources of literature, a review was put together concerning the effects of warming climate on zoo- and phytoplankton interaction in temperate lakes. Main objective was to confirm the hypothesis stating that warming climate causes a decrease in zooplankton grazing control on phytoplankton development in temperate lakes. According to many research publications, global air and water temperatures are in the process of ascension. Global warming and its coeffects play an important role in shaping the physical, chemical and biological characteristics of lakes, which can promote eutrophication. One of the consequences of eutrophication is a rise in phytoplankton production and biomass. This in turn can develop into seasonal, sometimes toxic, blooms of phytoplankton, such as diatoms and cyanobacteria. Extended periods of algal proliferation caused by warming climate can damage water quality, reduce biodiversity, diminish fisheries and clean water reserves. Generally, zooplankton has an essencial part in limiting phytoplankton biomass. As a result of warming climate, the potential restructuring of lacustrine food webs and perhaps those of all aquatic ecosystems is the most feared outcome of global warming. Many publications seem to point out that in many temperate lakes, global warming is likely to cause a temporal mismatch in seasonal dynamics of phyto- and zooplankton. The most important changes in plankton dynamics coincide with spring, where decisive conditions are being set. Phytoplankton vernal biomass maxima have shown an earlier occurence compared to those of the zooplankton. Normally, a syncronous development of spring biomass peaks of these plankton groups would occur at the same time if zooplankton were to achieve efficient grazing control over phytoplankton biomass. Beside alterations in seasonal timing of zoo- and phytoplankton communities, the changes in algal community compositions towards dominance of less edible forms like filamentous and colonial cyanobacteria, and the icreased top-town control over zooplankton by planktivorous fish favouring the smaller species will further affect the zooplankton and phytoplankton trophic relationships in a warmer climate. Together with the increased risk of more intense and toxic cyanobacterial blooms and longer exposure to parasites due to increased water temperature this will likely select for better adapted zooplankton in a future climate change. Increasing water temperature will therefore severely affect the zooplankton and phytoplankton relationships in a warmer climate. In the light of the literature analysed the proposed alterations in the grazer community dynamics and structure, either caused directly by rised water temperature or indirectly via food web interations, will likely result in weaker control over phytoplankton development in temperate lakes in a warmer climate. Since many publications seemed to be in accordance with this, and there seemed to be no discrepancies in sources studied on that particular aspect, the hypothesis was eventually considered as valid.