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Relationship between nematode community and biomass and composition of periphyton developing on artificial substrates in floodplain lake

Vidakovic J., Palijan G., Cerba D.

Polish Journal of Ecology

2011

Vol. 59, nr 3

577-588

Periphyton colonisation on artificial substrate (microscopic glass slides) was investigated from July to November 2007, in Lake Sakadas (Danube River floodplain Kopacki rit, Croatia). Two different stations were chosen due to different post - flood conditions. The aim of the study was to follow temporal changes of nematode community composition and trophic structure in relation to periphyton biomass and bacterial abundance. In bryozoan - dominated periphyton (Plumatella emarginata Allman, 1844) nematodes were represented by 86 and 87% of total associated invertebrate fauna at S1 and S2 respectively. Total nematode abundance (up to 600 ind. 10 cm[^-2] at one station and up to 1130 ind. 10 cm[^-2] at another station) correlated significantly with the abundance (meaured as CFUs - colony forming units) of copiotrophic and oligotrophic bacteria at one station (r = 0.963, 0.998, P <0.05) and with organic and inorganic content of periphyton at another station (r = 0.891, 0.899, P <0.05). Nematode trophic groups (epistrate feeders, chewers, detritus feeders and suction feeders) were equally developed at both stations except detritus feeders whose species richness and abundance were significantly higher at the S1. Epistrate feeders were the most abundant trophic group in nematode assemblages at both stations with Chromadorina bioculata being the dominant species. Change in dominance of epistrate feeders by chewers (Brevitobrilus stefanskii) and suction feeders (Crocodorylaimus sp.) coincided with the occurrence of flood pulse. Effect of flood pulse on nematode community structure was probably indirect, alterating concentration of dissolved oxygen which chromadorids are sensitive to. The structure of nematode community developed through time differs between investigated stations indicating high sensitivity to bacterial abundance, periphyton biomass and P. emarginata mats which made the habitat more diverse and patchy.

The impact of inundation-isolation cycles on the culturable bacterioplankton in the Danube River floodplain

Palijan G., Bogut I., Vidakovic J.

Polish Journal of Ecology

2008

Vol. 56, nr 3

391-401

The investigation was conducted in the Kopacki Rit Nature Park (eastern Croatia) which is established to protect the floodplain area of the Danube River. The samples were collected monthly in four sites (channels and lakes) with increasing distance from the river. The aim of investigation was to examine trophic structure of culturable bacterioplankton in relation to inundation-isolation cycles on sampling sites with unequal degree of connection with the Danube river. A change in the ratio of copiotrophs (r-strategists) to oligotrophs (K-strategists) was expected as the different organic carbon sources emerged. The composition of variables was revealed by Principal Component Analysis of abiotic water properties (temperature, water depth, transparency, pH, electrical conductivity, dissolved oxygen, nutrient concentrations) and the chlorophyll-a concentration. Scores of significant components were used in a Multiple Regression as independent variables and the relationship between the scores and abundance of colony forming units (CFUs) was examined. Regression model was significant only for copiotrophs, and their relative dominance was noticed in couple of samples on more isolated sampling sites. In all other samples oligotrophs were a dominant group, especially during the flood pulses or drainage after it. Their elevated abundance was equally distributed in all groups revealed by Principal Component Analysis, and corresponds to the fluvial action. Also concerning the [eta] squared and R squared values from the two-way ANOVA (sites/samplings) oligotrophs are highly influenced by the sampling period i.e. inundation-isolation cycles. They are probably driven by the allochthonous organic matter provided by floods or have allochthonous origin itself. At the same time, copiotrophs are to some extent coupled with the established water properties, i. e. bottom-up controlled and their abundance is influenced by the localisation of sampling sites in the floodplain. These results describe the development of the conditions that promote habitat specific succession of the culturable bacterioplankton. Established differences had disappeared after additional inundation-isolation cycles.