Vertical distribution of zooplankton in a shallow peatland pond: the limiting role of dissolved oxygen

We investigated the diel vertical distribution patterns of microcrustacean zooplankton (Cladocera, Copepoda) in a shallow pond (max. depth: 70 cm) of the Öreg-turján peatland (Ócsa, Central Hungary) during three 24-h periods in July (19–20th), August (17–18th) and September (11–12th) 2011. Environmental variables showed remarkable vertical stratification. Oxygen concentration was close to zero in the entire water column from night until sunrise, while the lower strata (from 20 cm below the surface) were close to anoxic during all three diel cycles. It proved to be the main determinant of the vertical distribution of microcrustaceans. Accordingly, the highest proportion of individuals was present in the surface layer. Chlorophyll-a concentration and phytoplankton biomass were inversely distributed compared to zooplankton. Microcrustaceans (mainly Daphnia curvirostris) migrated to the middle layer only in August, which could be explained by a trade-off between food resources, dissolved oxygen (DO) and competition with littoral zooplankters. The diurnal density patterns of microcrustaceans suggested horizontal migration into the aquatic macrophytes during night, which could be a strategy to avoid Chaoborus predation. Our results show that strong vertical gradients of abiotic and biotic factors occur even in such shallow waterbodies. Among them, DO can maintain constant vertical aggregation of zooplankters by limiting their occurrence to the surface layers

A Tolna-Baranyai-dombvidék és a Kelet-Mecsek vizeinek kétéltű-faunisztikai vizsgálata

Between March and June 2012, we studied the presence of amphibian species in more than 100 waterbodies of the Tolna-Baranya Hills and the Eastern Mecsek. We included lakes, ponds, temporary pools, marshes as well as streams in our survey and considered all developmental stages of the inhabiting species. We found nine amphibian species in the whole territory. The two most common species were the water frog complex (Pelophylax esculentus complex) and the agile frog (Rana dalmatina). One of our most important results was proving the occurrence of yellow-bellied toad (Bombina variegata) in the Szekszárd Hills. The amphibian fauna was lesser-known in this region, thus our results are important for both biogeography and nature conservation