| Popis: |
We observed changes in the composition, structure and seasonal succession patterns in the community of interstitial ciliates in the White Sea over a period of 18 years. Considerable inter-year fluctuations of species abundances as well as species richness, diversity, trophic and size structure were recorded. During the first 12 years, the changes appeared to be multi-vectorial. However, in the last 6 years the community modification became direct, with an increasing number of specific interstitial ciliate species, and Trachelocerca sagitta as the leader. These changes were caused by the increase in the silt content and the amount of dead organic matter, as well as by the decrease in the concentration of oxygen and the size of interstitial spaces in the sediments. All the changes took place on the background of the same set of ciliate species and the same niche structure. The changes in the community structure during the period equivalent to thousands of generations of ciliate populations are realized through two major mechanisms. The first one acts through inter-annual fluctuations, and manifests itself in recombinations of species composition in response to local environmental factors. The second one acts through long-term directional changes in the community composition, in accordance with the trended transformations of the littoral ecosystem. Inter-year changes (e.g., the degree of seasonal fluctuations of abundance, species diversity and community structure) were also manifested at all the stages of seasonal succession. During the last 6 years, within-year variability of abundances clearly increased, and so did stability and direction of seasonal succession. Yearly renewed seasonal successions do not lead to the increase in the community complexity and order, but are rather stages on the way of the communitys adaptation to the changing environment. Inter-year variability of the patterns of seasonal succession reflects the evolutionary potential of the communitys resilience in a fluctuating environment. |
