Checklist of Baltic Sea Phytoplankton Species - Helcom

Introduction
Two previous checklists of Baltic Sea phytoplankton (Hällfors 1980 (1979) and Edler et al. 1984) were
titled ”preliminary”. Our knowledge of the taxonomy and distribution of Baltic Sea phytoplankton has
increased considerably over the last 20 years. Much of this new information has been incorporated in
this new list. Data from a number of older publications overlooked by Edler et al. (1984) has also been
included. As a result, the number of species included has grown considerably. Especially the inclusion
of more estuarine species adapted to salinities lower than those of the open Baltic Sea has increased
the number of species. The new list also contains species which mainly grow in ice but form sparse
planktonic populations in the beginning of the spring bloom, and species of benthic or littoral origin
(whether epiphytic, epilitic, epipsammic, epipelic, or rarely epizooic), that are occasionally found in the
plankton. The benthic and littoral species are coded with an ”l” in the checklist. Concerning the diatoms,
especially in the order Bacillariales, it is usually impossible to tell whether the cells of such species have
been alive when sampled because of the preparation techniques (including the removal of cell contents)
required for an accurate determination.
Whereas the two previous lists were based to a large extent on our own unpublished information, in
this list only additional published data has been included. Altogether the new list contains more than
three times as much information as the earlier lists. Author citations have been made as complete as
possible. In a complete author citation the Latin prepositions in and ex are frequently used. In indicates
that the author has validly published a new taxon in another writer’s work. The use of ex indicates that
a name was invalid e.g. because an original description or type was not provided, but the situation
was later corrected by the same or another author. In some cases the distinction between ex and in
may be very fi ne, and requires careful study of the original publications, and sometimes even of the
types, if indeed they exist any more. World War II appears to have destroyed many types. Where
shorter citations are needed to save space, everything before ex and after in can be excluded, as well
as the year of publication, unless nomenclatural or taxonomical changes are involved. Many journals
require authorships to be cited either when the species occurs for the fi rst time in the text, or in a
summarizing table covering all the organisms mentioned. In many routine cases merely a reference to
an authoritative checklist may be enough.
The factual and typographical errors found in the previous list (Edler et al. 1984) have been corrected,
and the annotations revised. Annotations nowadays considered to be common knowledge have been
deleted, while new comments have been necessary e.g. in several taxonomically complicated cases.
Furthermore the list of references has been extended considerably.
Because many old original publications are no longer easily available, certain data is missing from
some citations. Determining publication years has been particularly problematic. Often the year of a
particular volume has been cited instead of the year when the issue in question was actually published,
and these dates may differ by several years. Such problems cannot be solved without access to the
individual issues. When bound, the covers of the issues are usually lost, and thereby information
on the date of publication. This is a problem e.g. with Ehrenberg’s publications from the mid 1800s,
and A. Schmidt’s Atlas from the late 1800s and early 1900s. Even the relatively recent Rabenhorst’s
Kryptogamenfl ora suffers from the same problem. In some cases an article has been divided between
two issues printed in subsequent years. In rare cases even the description of a new species has been
split in this way. I have tried to express this by putting an alternative publication year in brackets, or in
the case of a species description being split, using a dash between the years.
The fact that organisms included in the checklist have been described either as a plant according to the
International Code of Botanical Nomenclature (ICBN), or as an animal according to the corresponding
zoological code (ICZN), may in some cases give rise to problems. The botanical code requires a Latin
diagnosis for a name to be valid, whereas ICZN does not. Thus the validity of the name of an organism
sometimes depends on whether it is today considered to be a plant or an animal. Sometimes the usage
or spelling of even valid names may vary (see e.g. Vørs 1992:370). In fl agellated organisms the use
of two different codes is clearly a problem, when the same cell, depending on external factors, may
behave as a plant (autotrophic, photosynthetic) or an animal (phagotrophic), or something in between
(mixotrophic).
5