Zooplankton of the open Baltic: Extended Atlas - IOW

Several investigators observed that ciliate abundance in the water
column was positively correlated with the chlorophyll a concentration that
increased with productivity and eutrophication (Arndt, 1991; Garstecki et al.,
2000; Samuelsson et al., 2006).
As it was shown for different parts of the Baltic Sea, large ciliates
would increased in numbers with increasing primary production, while the
bacterial production would govern the dynamics of small ciliates (Witek,
1998; Johansson et al., 2004; Samuelsson et al., 2006). Seasonal succession of
ciliate community from large predatory ciliates in spring to small
microphagous and epibiotic ciliates in summer is typical and was revealed for
the northern (Johansson et al., 2004; Samuelsson et al., 2006), southern
(Witek, 1998) and western Baltic Sea (Smetacek, 1981).
Even though the growth rate of ciliates in summer seemed to be mainly
limited by the amount of the resources in a coastal area, the biomass of
ciliates in the northern Baltic Sea was found to be strongly affected by
predation of mesozooplankton. Studies in the Baltic Proper suggest that the
ciliate biomass is top-down predation-controlled, while the production may be
bottom-up limited by the resources (Samuelsson et al., 2006).
Role in zooplankton communities
Analyses of the results of various recent studies in the pelagic regions
of the Baltic Sea revealed that the protozoan biomass had been in the same
range or even higher than mesozooplankton biomass (Arndt, 1991). For
example, in the south-western Gdańsk Basin the heterotrophic ciliate
community contributed 10 to 13% to the mean annual zooplankton biomass
(Witek, 1998). In the Neva Bay, nearly 16% of the total destruction of organic
matter accounted for planktonic ciliates (Khlebovich, 1987). Interestingly, it
exceeded the joint decomposition of organic substances by rotifers,
cladocerans and copepods (10%). Daily average ciliate production was 0.25
mg/l or 50 mg C/m 2 per day. It formed nearly 19% of primary production of
phytoplankton and about 30% of bacterial production (Khlebovich, 1987). In
the Gdańsk Basin, carbon demand of non-predatory ciliates calculated
according to their potential production was estimated to be equivalent to 12-
15% of the gross primary production (Witek, 1998).
Some unresolved research problems in ecology of Baltic ciliates
During the last decades many researches have been involved in the
study of functions and role of ciliates in the Baltic pelagic ecosystems. Thus,
major interest has been centered around the structure of microbial loop.
Several studies were devoted to experimental investigation of nutrition of
Baltic ciliates and mainly concerned with their role as predators (Kivi &
Setala, 1995; Aberle et al., 2007; Moorthi et al., 2008). In particular, these
investigations deal with food spectrum, herbivore selectivity and grazing
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