Zooplankton of the open Baltic: Extended Atlas - IOW

eautifully designed network of flows among many different kinds of
bacterial decomposers” (p. 14).
Thus, already in the second half of the XX century scientists around the
Baltic were admitting that the real diversity of microscopic invertebrates in
plankton might happen to be much higher when special biodiversity
investigations are performed. This idea was later supported by the results of
the long-term zooplankton diversity and ecosystem functioning research in
the eastern Baltic coastal waters which demonstrated high species richness of
pelagic communities in major Baltic estuaries and other coastal ecosystems
(for details see the review publications: Telesh, 1987, 1988, 2001, 2004,
2006a, 2006b; Telesh & Heerkloss, 2002; Telesh & Heerkloss, 2004; Telesh
et al., 2008).
However, until recently attempts to evaluate the total zooplankton
diversity including the unicellular organisms in the open Baltic Sea have
hardly been made. Zooplankton diversity in the Baltic Sea has been routinely
described in terms of dominant species of certain groups (mainly copepods)
and size fractions (mesozooplankton) that are identified and counted for
monitoring purposes (see Chapter 2). Presently, geographical coverage of the
Baltic Sea, as well as of other European seas is still incomplete for Protista,
Rotifera and Brachiopoda (Costello et al., 2006).
Meanwhile it is widely accepted that assessment of zooplankton species
diversity provides important information on the marine ecosystem structure,
trophic webs and functions, and their natural and/or human induced
alterations. In many zooplankton groups, major functional characteristics
responsible for the animals’ behaviour and interactions within the community
are species-specific, therefore the importance of correct taxonomic
identification of zooplankton, especially of key species, indicators of water
quality, and non-indigenous species can hardly be overestimated.
On the basis of data published in the first edition of zooplankton atlas
of the open Baltic Sea (Telesh et al., 2008b) we can conclude that the earlier
existing conception of the low species diversity of planktonic communities in
the Baltic Sea had resulted from the insufficient knowledge on the species
composition of zooplankton, particularly its small-size fraction (Telesh, 2008;
Mironova et al., 2009; Telesh & Skarlato, 2009).
It is commonly accepted that a marine zooplankton community is
formed by the following size fractions: picoplankton (size of organisms 0.2-
2.0 µm, mainly heterotrophic bacteria), nanoplankton (2.0-20.0 µm,
heterotrophic nanoflagellates), microplankton (20-200 µm, ciliates and a
large part of rotifer species), mesozooplankton (0.2-20.0 mm, larger rotifers,
mainly planktonic crustaceans, meroplanktonic larvae of some benthic
invertebrates, etc.), and macrozooplankton (organisms larger than 20 mm:
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