Zooplankton of the open Baltic: Extended Atlas - IOW

Sessilid ciliates also can be numerous in the Baltic plankton, especially in late
autumn and early winter (Mamaeva, 1987; Witek, 1998; Johansson et al.,
2004). Apparently at this time the peak of abundance of large filamentous
cyanobacteria and intensive water mixing provide particles for sessilid ciliates
to grow on.
Specificity of assemblages
The proximity of bottom and the availability of hard substrates greatly
influence the ciliates’ community composition. Near the bottom the ciliate
community changes from dominance of the open water Balanion to Euplotes,
which is known to occur in epibenthos (Samuelsson et al., 2006). There are
several possible reasons for the decrease of the open water ciliates. It can be
caused by an indirect effect due to changes in the prey community, or the
excess surface may have influenced their swimming behaviour negatively
(Samuelsson et al., 2006). Similar results were obtained by Klinkenberg and
Shumann (1994). This study showed that in the bottom layers larger benthic
and particle-associated ciliates (e.g. Euplotes, Oxytricha, Blepharisma) had
developed whereas in the supernatant relatively small ciliates like
Strombidium, Strobilidium, Mesodinium, Halteria and Askenasia had
remained present. In the Gdańsk Basin, the deep-water ciliate community
composed of Prorodon-like ciliates and Metacystis sp. also differed from the
community of the epipelagic layer (Witek, 1998). Similarly, ciliate population
structure in the anoxic depths of the central Baltic Sea (below 120 m)
completely differed from those in the upper layers (Detmer et al., 1993).
Substancially lesser number of ciliate species was found at this oxic/anoxic
interface. Among them several specimens of the genus Metopus were
recognised (Detmer et al., 1993). The deep-water associations in the
Bornholm Basin were composed of larger-sized ciliate species if compared
with the upper water layers (Setala & Kivi, 2003).
Indicators
There are several indicator species among the Baltic ciliates
(Khlebovich, 1987; Boikova, 1989). For example, the presence of
Tintinnidium fluviatile in some parts of the Neva Bay means that those waters
are oligosaprobic. Such species as Tintinnopsis cratera and Strombidium
mirabile (from the Neva Bay) are also indicators of clean water. Ciliates
Dexiostoma campylum (Plate 4.3.6), Colpoda steini, Coleps hirtus (Plate
4.3.1), Halteria grandinella (Plate 4.3.13) are, on the contrary, indicators of
polluted water (Khlebovich, 1987). The bloom of the autotrophic ciliates
Myrionecta rubra is the evidence of eutrophication. It should be noted that in
the central Bornholm Basin this ciliate dominated during spring and summer
reaching maximum biomass of about 0.2 – 0.3 mg C/l (Beusekom et al.,
2007).
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