| Summary: | This study was conducted in order to define the most important factors responsible for
the zooplankton community structure inhabiting four meteorite crater ponds, located near
the city of Poznań (Poland). The functioning of the meteorite craters resembled that of
other small water bodies, where seasonality, physical-chemical features (mainly
chlorophyll a concentration, pH and conductivity) or biological
parameters (lack of fish) structured zooplankton assemblages. Rotifer species richness and
abundance were highest in the autumn (12 species and 5107 ind L-1 on average),
while crustaceans prevailed in the summer (12 and 201, respectively). The dominating
structure also depended on the season, with pelagic species occurring in the spring and
autumn and mainly littoral species in the summer. Moreover, the temporary nature of the
craters caused great differentiation in zooplankton among ponds and favoured organisms
adapted to living in astatic reservoirs, e.g. bdelloids, Daphnia
pulex or Macrocyclops viridis. The co-occurrence of a variable
community of small crustaceans with large daphnids indicated the existence of an
additional ecological niche – a thick layer of sediments. Despite the occurrence of
adverse living conditions (oxygen deficiencies and periodic drying) and the eutrophic
character of the waters, these ponds were a source of many rare species (e.g.
Keratella paludosa), even in the status of dominants. Protective measures (a
nature reserve) allowed the area of meteorite fall to remain quite natural, despite its
location close to an urban area.
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