engleski

Recovery of meiofauna after anoxic stress. II. Spatial distribution

Beckground and purpose: Progressive oxygen depletion that occurred during the summer and autumn of 1989 in the central and eastern part of the northern Adriatic Sea culminated by the end of November in a short-term (two weeks) but extensive (1200 km2) anoxic event. In the area most affected by oxygen deficiency the composition and density of meiofauna were examined at three offshore stations (005, 007 and 107) at 30-36 m depth. Attention was focused to the spatial aspect of recovery dynamics during the biennial postanoxic period. Material and methods: Sediment cores (10 cm long, 10 cm2 area) we! re collected by divers with plastic hand-corers, from November 1989 till December 1991. Each sample was divided into six one-centimetre sections, and a residual one involved part of a core at a 7-10 cm depth. The material was treated by standard laboratory procedure including fixation, elutration, sieving (100 and 50 ľm mesh sizes), counting and classification of the main meiofaunal taxa under a dissecting microscope. The raw data i.e.means of three replicates per sample were subjected to statistical analyses. Results and conclusions: The temporal variability of meiofauna stratification was considered. Vertical distribution patterns are described. The results concerned monthly, occasional ("stagnation" vs. "recovery") and biennial intervals, and suggested a clear vertical gradient of meiofauna densities at all compared instances. Most of the organisms were confined to the uppermost 3 cm of the sediment core, attaining a disti! nct maximum between 0 and 1 cm depth. The means in each particular layer within the sediment core were at least by half, even by two thirds lower in comparison to the previous one. Only the nematodes penetrated to a 10 cm depth. Copepods, ostracods and kinorhynchs showed a clear affinity towards a sediment surface. The study of temporal distribution of meiofauna density suggested considerable variations within particular sediment layers with statistically significant differences between "stagnation" and "recovery" periods. The range and intensity of alterations in distributional patterns suggested that the recovery process occurred mainly in the three uppermost centimetres.

meiofauna; Nematoda; Copepoda; vertical distribution; anoxic event; recovery

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