engleski

The effect of anoxic event on meio - and nematofauna community structure

Progressive oxygen depletion, had occurred during the summer and autumn of 1989 in the central and eastern part of northern Adriatic, culminated by the end of November in a short-term (two weeks) and extensive (1200 km2) anoxic event. The influence of anoxia on sediment living meio- and nematofauna was studied at three stations (005, 007 and 107) in the midpoint of affected area. Special attention was paid to the recovery process. In 1197 sediment subsamples, collected from November 1989 till December 1991, 186.408 meiofauna and 12.350 nematofauna specimens were counted and classified. Examinations involved the qualitative and quantitative composition of meiofauna, nematofauna and free-living nematode populations. Attention was focused to spatial and temporal aspects of recovery dynamics. The main population parameters (density, dominance, frequency, spatial distribution, age classes) and a coenological ones (composition, abundance, species richness, evenness, diversity, feeding categories and similarity) were studied. The results were subjected to univariate, multivariate and distributional methods. The stations compared were characterized by similar environmental features and similar faunistic composition. During the investigations a similarity related to spatial and temporal dynamics of meio- and nematofauna was also established. A very close pattern was found out related to the intensity of stress response and communities alterations during the recovery. The effects of anoxia were manifested in a decrease in diversity and density (about 90%). Quantitatively, two main periods of recovery - connected by an interval involving a sudden "abundance explosion" 7-9 months after the anoxic event- could be distinguished. The alterations of qualitative and coenological parameters were successive and less expressive. Qualitatively it was a permanent, long-term and complex process - with no expressive alterations and distinctive succession phases. Free-living nematodes, especially competitive dominants, were recognized as the main promotors of the recovery process. Meio- and nematofauna can be successfully applied as indicators of anoxic stress conditions.

meiofauna; free-living marine nematodes; northern Adriatic; community structure; anoxia; recovery dynamics

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