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Rotifera of lake psammon:
community structure versus trophic state of lake waters |
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Jolanta EJSMONT-KARABIN |
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Centre for Ecological Research, Polish Academy of
Sciences, Hydrobiological Station, Leśna 13, 11-730 Mikołajki, Poland,
e-mail: jolantaek@poczta.onet.pl
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Abstract: Rotifer communities inhabiting wet sands of lake beaches are dependent
in their functioning on permanent input of organic matter from neighbouring
sites. The aim of the study is to test the hypothesis that trophic state of
lake waters may influence densities and structure of psammon communities of
Rotifera. Studies were carried out in hydro-, hygro- and euarenal of 44 beaches
in 18 lakes of different trophy in summer 1999 (since 2 till 17 July) and 38
beaches in 16 lakes in spring 2000 (since 10 till 23 May). Psammon was
sampled always between 10 a.m. and 2 p.m. at similar weather conditions (no shadow,
rains and strong winds). Interstitial waters were mostly alkaline and contained less oxygen
than lake ones and oxygen concentrations decreased upward water line. Very
high variability of phosphate P content made differences between trophic
groups of lakes not significant. Similarly, concentrations of P total were
more or less similar in all studied trophic groups of lakes. Total nitrogen
values were increasing from meso-eutrophic to hypertrophic lakes in spring,
whereas this trend was not observed in summer. Chlorophyll a concentrations were similar in
meso-, meso-eu- and eutrophic and markedly higher in hypertrophic lakes. In general, some tendency to increasing values of chemical parameters
with increasing trophy may be seen if their ranking list is compared. Rotifers
were present in all the studied stations. In total, 110 species (i.e. ca. 26% of all records of rotifer
species in Poland) were found with 22 species occurring exclusively in
psammon. Three species new in rotifer fauna of Poland were discovered - Cephalodella psammophila, Collotheca
wiszniewski and Euchlanis dapidula.
Generally
all trophic groups of lakes were relatively similar as regards species
structure of rotifer communities with rotifers of the genus Lecane playing most important role.
The index of Percentage Similarity of Community calculated for randomly
chosen 30 pairs of particular beaches from the same lake and for beaches of
different lakes was in both cases almost identical. Species of
high frequency constituted the overwhelming majority of individuals forming
rotifer communities of all beaches. Forms met in 1 to 5 lakes decided on
faunistic originality of the communities. Some tendency was observed for
higher diversity of psammon rotifer communities in mesotrophic and eutrophic
lakes. The lowest values of diversity index occurred mostly in hypertrophic
lakes. Psammobionts constituted only 20% and psammoxens 10% of the community
numbers in all lakes and all zones of the beaches, whereas psammophilic
rotifers decidedly dominated (70%). Rotifer
numbers were relatively similar in eu- and hypertrophic lakes and markedly
higher in mesotrophic and lower in meso-eutrophic lakes. However, due to high
fluctuations of the values noted in particular beaches the differences were
not significant in any of the possible configurations of compared data.
Monogononta played much more important role in rotifer densities than
bdelloids. The hypothesis on advantageous influence of high
trophy of lake waters on abundance of psammon communities of Rotifera cannot
be supported by results of this work. In lakes of moderate trophy (from meso-
to eutrophy) the amount of nutrients and chlorophyll does not seem to
influence psammon communities. In hypertrophic lakes this impact is observed,
but it seems to be rather unfavourable for psammon rotifers. The communities
in hypertrophic lakes are poorer in species, less diversified and less
original. The group of animals developing well in this group of lakes are
bdelloids. |