Zooplankton of the open Baltic: Extended Atlas - IOW

4. CILIATES OF THE BALTIC SEA
4.1. Brief characteristics of planktonic ciliates of the Baltic Sea
General information
Planktonic ciliates play pivotal roles in the transfer and recycling of
carbon and other nutrients in the seas. It is now well established that ciliates
constitute an essential food link in marine environments since they remove a
significant part of primary and bacterial production and assume ‘trophic
repackaging’ of picoplankton particles (0.2–2.0 µm) otherwise inaccessible to
mesozooplankton. Picoplankton organisms (heterotrophic bacteria,
cyanobacteria, phytoplankton of cell size 0.2–2.0 µm) are the major
consumers of dissolved organic matter; their biomass and production is the
largest within the total planktonic community. Ciliates, which are among the
most important consumers of this production, play a key role as an
intermediate stage in the transformation of organic matter from picoplankton
to higher trophic levels.
Firstly, ciliates have high growth and metabolic rates. Secondly, they
belong to a size range easily removed by metazoans, therefore they constitute
a significant part of the food biomass in the sea. Planktonic ciliates make an
essential contribution to the nutrition of copepods, rotifers, other invertebrates
and fish larvae. Along with phototrophic microorganisms, viruses,
heterotrophic bacteria, and microscopic fungi, ciliates participate in a
‘microbial loop’, which is an integral part of the planktonic food webs.
Furthermore, the importance of planktonic ciliates as indicators of
eutrophication and water pollution has been emphasized.
History of research
Pioneering studies of planktonic ciliates in the Baltic Sea began in the
late 1940-s (Biernacka, 1948). Most of them dealt with Tintinnids because of
their relatively large size (Biernacka, 1948, 1952; Hedin, 1974, 1975). There
were also researches of other groups of ciliates (Bock, 1960; Biernacka,
1963). Investigations of benthic ciliates began earlier, in the late 1920-s
(Sauerbrey, 1928; Kahl, 1930-1935). Contemporary investigations of Baltic
ciliates deal with both, benthic communities (Klinkenberg & Schumann,
1994; Dietrich & Arndt, 2000; Garstecki et al., 2000), and planktonic ciliates
(Smetacek, 1981; Boikova, 1989; Arndt, 1991; Kivi & Setala, 1995; Uitto et
al., 1997; Witek, 1998; Setala & Kivi, 2003; Johansson et al., 2004;
Samuelsson et al., 2006; Beusekom et al., 2007). Benthic and pelagic
communities of ciliates showed little taxonomic overlap (Garstecki et al.,
2000). However, benthic ciliates (genus Euplotes, Aspidisca, Tracheloraphis
etc.) may be found in the water column because of bottom hashing; their role
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