Diversity and zooplankton species associated with certain hydroperiods and fish state in field ponds

In order to establish conditions responsible for zooplankton occurrence in field ponds subjected to FP (three categories of ponds: fish-free; low fish stocking; high fish stocking) and WR (two categories of ponds: permanent vs. temporary), material was collected from the open water of six neighbouring ponds, thirteen times in 2009, covering the spring, summer and autumn. A total of 134 zooplankton taxa was recorded with rotifers (94 taxa) prevailing taxonomically over cladocerans (24) and copepods (16). A tendency of certain taxa and species diversity to group along a gradient of WR and FP was observed. Higher species diversity was attributed to fish-free ponds, partly depending on the higher contribution of macrophyte-dominated areas, which are known to support a high variation of organisms. Two groups from among the most frequent species that indicated temporary ponds were: 1/littoral-associated (e.g. Lepadella ovalis, Chydorus sphaericus) in fish-free ponds and 2/large-bodied mainly pelagic (e.g. Eudiaptomus gracilis) in low-fish ponds. Fish ponds that were of permanent character, however, had lower species richness, with a high frequency of typically eutrophic taxa such as Brachionus angularis, Keratella cochlearis f. tecta or Trichocerca pusilla. However, they were also a source of rare species such as Brachionus falcatus, Lecane tenuiseta, Ceriodaphnia dubia that occurred exclusively in these ponds compared to natural fish-free ponds, which were remnants of lost species richness. This in turn increased overall zooplankton richness in the regional aspect. Thus, the co-occurrence of temporary ponds along with fish-production targeted permanent ponds may lead to a rise in zooplankton biodiversity on a local scale. We assume therefore that not only patterns of zooplankton biodiversity but also the occurrence of particular species can be treated as a useful indicator of FP and WR in small water bodies and are crucial for conservation purposes and management of aquatic systems at regional and landscape levels.