engleski

Field study on the population dynamics of sedlected nematodes species: post hoc approach to assessment of acute oxygen deficiency impact

Population dynamics of selected nematode species was monitored at three northern Adriatic offshore sites during biennial post anoxic period. The study was performed with an aim to assess a population-specific resistence to oxygen deficiency, and to reveal a relative importance of particular species in the subsistence and recovery of nematofauna assemblages. A temporal variability of main population parameters, i.e.abundance, dominance and constancy was taken as a starting point for the assessment of both issues. Special attention was paid to temporal distribution of gravid females and immature specimens as a supposed positive indicators of recovery process. Quantitative analysis of total nematofauna pointed out two distinctive phases of succession: stagnancy - distinguished by insignificant signs of improvement manifested in abundance ranging from 51 to 356 ind./10 cm2, and a recovery characterized by conspicuous monthly oscillations and abundance ranging from 622 to 2884 ind./10 cm2. Population dynamics were analysed following the same temporal pattern, i.e. stagnancy vs. recovery. Among total 168 species recorded during the investigation, 49 species with dominance >5% in one or more samples were recognized as potentially suitable indicators for achievement of subsistence to acute oxygen deficiency as well as following recovery. A comparison of population parameters associated with defined phases of succession pointed out three distinctive patterns of population's strategy. The first pattern was distinguished by statistically significant increase in population densities after the period of stagnancy. The second pattern was characterized by a significant decrease in population densities during the same period. The third pattern was distinguished by absence of statistically significant differences in density of remaining populations between two compared periods. Conformably to such occurrences, species exhibited single population strategy and should be regarded as sensitive, opportunistic or tolerant in respect to acute oxygen deficiency. Species disposed in two last groups had an important role in the subsistence of nematofauna after the anoxic stress, while species denoted as sensitive were recognized as main promotors of the recovery. Thus, in lack of pre disturbance information, post hoc studies on the population dynamics of selected nematode species might be a prospective means for the assessment of acute oxygen deficiency effect.

Nematoda;population dynamics;oxygen deficiency; northern Adriatic

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