engleski

Current velocity and food supply as factors affecting the composition of macroinvertebrates in bryophyte habitats in karst running water

In the lotic aquatic biotopes on a tufa barrage in the Plitvice cascade lake system macroinvertebrate samples associated with a calcareous substrate covered with bryophytes and accumulated organic detritus were collected seasonally in four habitats with different current velocities. The aim was to investigate the interaction between the community features of macroinvertebrates and bryophyte cover associated with the selective retention and accumulation of particulate organic matter affected by different water flow conditions. In the tufa barrage habitats, depending on current velocity, bryophyte biomass varied seasonally from 55 g AFDW m-2 to 256 g AFDW m-2. Bryophyte biomass decreased in the tufa habitats exposed to higher current velocity. In the temporal succession from spring to autumn bryophyte biomass decreased, whereas in winter the biomass increased in all studied rheotopes. Regression analysis suggested that the bryophyte biomass significantly decreased linearly with an increase in current velocity. The bryophyte mats, which retained coarse (CPOM), fine (FPOM) and ultra fine (UPOM) benthic particulate organic matter as a food source for the detritial benthic macroconsumers, were significantly related to current velocity. CPOM and FPOM content of the bryophyte mats showed a tendency to increase in habitats with a lower current velocity. Conversely, UPOM content increased in bryophyte habitats with a higher current velocity. Regression analysis suggested that CPOM and FPOM increased whereas UPOM decreased significantly in habitats with a greater bryophyte biomass. In bryophyte habitats the community composition of macroinvertebrates was characterized by small forms of oligochaetes, dipterans and coleopterans constituting from 64.1% to 98.7% of the total number of macroinvertebrate individuals. Regression analysis suggested that macroinvertebrate density increased in faster water flow conditions associated with a decrease in bryophyte biomass, CPOM and FPOM, and an increase of UPOM. Macroinvertebrate community composition and species diversity showed significant differences among the four seasons and four water flow conditions associated with selective retention and accumulation of POM. In bryophyte habitats macroinvertebrate functional feeding composition was characterized by collector fauna increasing their density with faster water flow conditions. In spring and summer collector gatherers were dominant whereas collector-filterers dominated in autumn and scrapers showed a maximum in winter. Regression analysis, using the power model (y = axb), suggested that densities of collectors and predators showed a positive relationship with the quantity of their food sources.

Aquatic bryophytes; macroinvertebrate community; functional feeding composition; karstic tufa biotopes

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