The First Settlers of Newly Built Pools: Zooplankton and Phytoplankton Case Study in Southern Moravia

The biodiversity of pool ecosystems is nowadays fully dependent on building of new ones or reconstructing the damaged ones. Among the factors influencing the potential of being colonised are the habitat's local characteristics including abiotic and biotic factors. One of the most important key roles in the food chains of freshwaters play zooplankton and its high dispersal rate makes them successful colonists of new habitats. Together with phytoplankton and nutrient content development, the state and following evolution of pool ecosystem can be assessed. The aim of this study was to survey initial zooplankton succession of newly built pools and to assess the main influencers on its colonisation success. Two newly built pools (Pool 1 and Pool 4) with different morphometric characteristics were monthly sampled for zooplankton, phytoplankton and physico-chemical characteristics. Zooplankton individuals were sorted according to taxa and stage as cladocerans, copepods (adults), nauplii and rotifers; and according to size structure as follows: < 0.5 mm, 0.5-1 mm, 1-2 mm and > 2 mm. Phytoplankton species were sorted in five categories: cyanobacteria, cryptomonads, green algae, diatoms and other algae. Basic physico-chemical parameters were measured and nutrient analysis were carried out. In Pool 1, first colonists were rotifers, followed by various cladoceran taxa. Rapid increase of large cladoceran species occurred in late spring. Till the end of the survey, rotifers together with nauplii predominated. Larger copepods were constantly present since late spring. In Pool 4, first colonists were rotifers, followed by copepod nauplii which predominated till the end of survey. Larger zooplankton species peaked in summer. In the first season after inundation, the presence of a massive biomass of charophytes and subsequently green filamentous algae was crucial for the development of the communities in both pools - significantly reduced the development of phytoplankton, caused high water clarity and affected the development of zooplankton. Because there were nutrients released from the sediment nutrient pool inflicted by fertilisation of intensively farmed field, significant fluctuations in pool ecosystem were observed. Also the morphometric characteristics of the pool, such as size, shape, depth and slope of the shores indicated the suitability of the habitat for successful zooplankton colonisation.