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Botanica Marina 2018; aop
Florian Weinbergera,*, Sophie Steinhagena, Dmitry F. Afanasyev and Rolf Karez
New records from the southern North Sea and
first records from the Baltic Sea of Kornmannia
leptoderma
https://doi.org/10.1515/bot-2018-0019
Received 26 February, 2018; accepted 28 August, 2018
Abstract: Combined genetic, morphological and ontoge-
netic observations show that the circumarctic boreal
green algal macrophyte Kornmannia leptoderma has
expanded its distribution range into the Baltic Sea, on
a German coastal section of 220 km length. The species
is also again (or still) established at its former extreme
southern distribution limit in the North Sea, the German
island of Helgoland, where it has not been detected during
the last four decades. Macroscopic visible sporophytes of
K. leptoderma are nowadays present in the Baltic Sea and
at Helgoland from February to September, while they were
in the past only detected from February to May at Helgo-
land. This capacity for formation of sporophytes in sum-
mer correlates with the circumstance that K. leptoderma
from the Baltic Sea can complete its life cycle at 15°C while
several studies conducted decades ago with material from
Helgoland and from Pacific coasts consistently reported
an inhibition of the algal gametogenesis at temperatures
that exceed 12°C. Possibly K. leptoderma has undergone
adaptations that facilitate its spread into warmer environ-
ments, unless the Kornmannia present in the Baltic Sea
and on Helgoland today represents a newly introduced
cryptic species.
Keywords: Baltic Sea; Kornmannia; marine invader; range
expansion; Ulvales.
Introduction
The SW Baltic Sea is an atidal brackish water environment
that offers similar temperature conditions to the SE North
Sea, although seasonal minimum and maximum temper-
atures are more extreme (Lennartz etal. 2014). Between
the Danish Straits and the Darss Sill at the German island
of Rügen, its mean salinity decreases over a distance of
approximately 300 km from more than 20 to 8 (Meier
and Kauker 2003). However, the surface salinities along
this relatively steep gradient vary considerably both in
time and space, due to changes in river runoff, periodic
seawater inflow from the North Sea, stratification and
upwelling. Many marine species reach their distribution
limit within this salinity gradient, which is not only the
reason for a decreased diversity (Schubert etal. 2011), but
often also for significantly reduced growth (Russell 1988)
and – especially in certain groups of macrophytes – for
other morphological changes (Russell 1994, Ruuskanen
and Kiirikki 2000).
Some green algal groups within the order Ulvales
are notorious for their morphological variability. Salin-
ity has repeatedly been reported to affect the morphology
of Ulvales (Burrows 1959, Reed and Russell 1978, Sanders
1979) and members of this order exhibiting “unusual” mor-
phologies have occasionally been reported from the Baltic
Sea. For example, in Finland green tides of the usually
tubular species Ulva intestinalis L. were observed that
exhibited a sheet-like monostromatic morphology (Blom-
ster etal. 2002). The variability of Ulvales often hampers
their identification based upon morphological charac-
teristics, which became apparent with the introduction
of DNA barcoding techniques into the field (Hayden and
Waaland 2002, Hayden etal. 2003). As a consequence, the
potential for cryptic introductions and hidden extinctions
of Ulvales appears relatively high.
We here report that our recently conducted revision
of the species inventory of Ulvales along the German
Baltic Sea coast resulted in the discovery of Kornmannia
leptoderma (Kjellman) Bliding which was so far not
known from this ecoregion. Kornmannia leptoderma was
first found on Novaja Zemlja, and originally described
aFlorian Weinberger and Sophie Steinhagen: These authors
contributed equally to this publication.
*Corresponding author: Florian Weinberger, Marine Ecology
Division, GEOMAR Helmholtz-Institute for Ocean Science,
D-24105Kiel, Germany, e-mail: fweinberger@geomar.de
Sophie Steinhagen: Marine Ecology Division, GEOMAR Helmholtz-
Institute for Ocean Science, D-24105Kiel, Germany
Dmitry F. Afanasyev: Department of Hydrobiology, Azov Research
Institute for Fisheries, Rostov-on-Don 344002, Russia; and
Department of Botany, Southern Federal University, Rostov-on-Don
344006, Russia
Rolf Karez: Landesamt für Landwirtschaft, Umwelt und ländliche
Räume des Landes Schleswig-Holstein, Hamburger Chaussee 25,
Flintbek 24220, Germany
Open Access. © 2018 Florian Weinberger et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution-
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2F. Weinberger etal.: Range expansion of Kornmannia
as Monostroma leptodermum Kjellman (1877), due to its
monostromatic sheet-like thallus that is composed of only
one cell layer. Later studies revealed major differences
among the life cycles of members of Monostroma (Korn-
mann and Sahling 1962, Tatewaki 1969) and, based on
its heteromorphic life cycle with a monostromatic sporo-
phyte and a disk-like gametophyte, M. leptodermum was
redescribed as K. leptoderma (Bliding 1968). Specimens
of the genus Kornmannia from the North Pacific (Wash-
ington) that lived primarily as epiphytes on seagrass
and other macrophytes and exhibited slightly divergent
morphologies were described as K. zostericola (Tilden)
Bliding (Bliding 1968). A later comparative study con-
cluded that the two species were indistinguishable with
respect to morphology and ontogeny (Golden and Cole
1986). Since then K. leptoderma is regarded as the only
taxon within the genus Kornmannia, but molecular com-
parisons of Atlantic and Pacific populations and type
specimens are still missing.
Kornmannia leptoderma has a circumarctic-boreal
distribution (Golden and Cole 1986), and in Europe its
documented southern distribution limits are in Norway
(Rueness etal. 2001) and at the Faroe Islands (Nielsen and
Gunnarsson 2001), with the remarkable exception of the
German North Sea island of Helgoland, at least 500km to
the South (Figure 1). At Helgoland K. leptoderma was prob-
ably observed for the first time in 1934 (Schmidt 1938) and
thereafter each year from 1960 (Kornmann and Sahling
1962) to 1966 and three more times in the 1970s (Korn-
mann and Sahling 1983). The species disappeared after
1977 and has been considered as extinct in Germany since
1996 (Ludwig and Schnittler 1996).
Materials and methods
Sheet-like monostromatic Ulvales and Ulothrichales were
collected during repeated samplings between Febru-
ary 2013 and September 2015 at 110 sites on the German
Baltic Sea coast between Flensburg and Rerik and at the
North Sea island Helgoland (Table 1). They underwent
microscopic examination in the laboratory and parts
were conserved for DNA barcoding. At 16sites material
was observed that could not be clearly assigned to Mon-
ostroma grevillei (Thuret) Wittrock – an abundant monos-
tromatic species in the area – and was investigated further
(Table 1, Figure1). To observe the algal life cycle, pieces of
approximately 1cm2 of the material collected at Mönke-
berg were transferred into glass Petri dishes (diameter
9cm) containing 40ml of ¼ strength Provasoli Enriched
Figure 1:Sites in Northern Germany where Kornmannia leptoderma has been collected.
Numbers 1 to 16 indicate the location of collection sites along the Baltic Sea shore that were visited since 2013 in the present study, as listed
in Table 1. Arrow indicates location of Helgoland in the North Sea, where additional samples were obtained at two sites in close proximity.
Dotted line represents the Kiel Canal.
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F. Weinberger etal.: Range expansion of Kornmannia3
Table 1:List of samples of Kornmannia leptoderma identified by DNA barcoding with information on sampling sites.
Date CollectorSite no.Site name EnvironmentCoordinates Temperature
(°C)
SalinityExposure Accession no.
..SST Kiekut Beach N °.′; E °.′..Semi-exposedMF
..SST Aschau Lagoon N °.′; E °.′..Protected MG
..SST Strande Harbor N °.′; E °.′..Protected
..SST Kiel-Falkenstein Beach N °.′; E °.′..Protected
.. FW Mönkeberg Harbor N °.′; E °.′..Protected MF
..SST Heiligenhafen, Binnensee Lagoon N °.′; E °.′..Protected
..DA Marina Heiligenhafen Marina N °.′; E °.′..Protected
..SST Heiligenhafen, Binnensee Marina N °.′; E °.′..Protected MG
..SST Heiligenhafen, Binnensee Marina N °.′; E °.′..Protected
.. SST Heiligenhafen, Binnensee Marina N °.′; E °.′..Protected
..SST Heiligenhafen, GraswarderLagoon N °.′; E °.′..Protected
..SST Heiligenhafen, GraswarderLagoon N °.′; E °.′..Protected
..SST Großenbroder Fähre Lagoon N °.′; E °.′..Protected
..SST Wulfen Lagoon N °.′; E °.′..Semi-exposed
..SST Marina Großenbrode Marina N °.′; E °.′..Protected
..SST Brodtener Ufer Beach N °.′; E °.′..Exposed
..FW Hohen-Wieschendorf Beach N °.′; E °.′..Semi-exposedMF
..DA Redentin Marina N °.′; E °.′..Protected
..DA Gollwitz Beach N °.′; E °.’′..Semi-exposed
..SST Helgoland, Südstrand Beach N °.′; E °.′..Semi-exposedMG
..SST Helgoland, Binnenhafen Harbor N °.′; E °.′..Protected MG
..SST Helgoland, Binnenhafen Harbor N °.′; E °.′..Protected
Collector: SST, Sophie Steinhagen; FW, Florian Weinberger; DA, Dmitry Afanasyev. Site no.: number in Figure 1. Temperature: temperature at collection time. Salinity: salinity at collection time.
Accession no.: GenBank accession number for tufA gene sequence included in Figure 3. Two lines printed in bold indicate samples used for life cycle studies.
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4F. Weinberger etal.: Range expansion of Kornmannia
Seawater (salinity17). The Petri dishes were maintained
for 15 months at 15°C, with a light regime of 40 μmol
photons m−2 s−1 (“cool white”, 12L:12D) and replacement
of the medium every 3months. The same approach was
repeated with identical cultivation conditions and material
collected at Heiligenhafen Binnensee on 30th August 2017.
Genomic DNA was extracted from material dried in
silica gel or from frozen fresh material, using the Invisorb
Spin Plant Mini Kit (Stratec, Birkenfeld, Germany) and fol-
lowing the manufacturer´s instruction protocol. DNA-bar-
code fragments of the plastid encoded elongation factor Tu
(tufA) were amplified by polymerase chain reaction (PCR),
using the primers tufGF4 (Saunders and Kucera 2010) and
tufAR (Famà etal. 2002). For amplification the following
temperature profile was used: initial denaturation 4min
at 94°C, 38 cycles of 94°C for 1min, 55°C for 30 s, 72°C
for 1min, final extension for 7min at 72°C. Sequencing in
both directions was provided by GATC biotech (Konstanz,
Germany). Sequences were assembled, reciprocally edited
with Sequencher (v. 4.1.4, Gene Codes Corporation, Ann
Arbor, MI, USA) and aligned, using the multiple sequence
alignment program MAFFT v. 7.311 (Katoh and Standley
2013).
Phylogenetic analysis
We analyzed the dataset using the Maximum likelihood
(ML) approach. For a robust analysis we included several
reference sequences downloaded from GenBank indi-
cated by their accession numbers. Reference sequences
of Bryopsis corticulans (accession number: HQ610243) and
Prasiola stipitata (accession number: GWS004831) were
used as outgroups. We constructed ML phylogenies with
RAxML v. 8 (Stamatakis 2014). As nucleotide substitution
model GTR + GAMMA was used. To test the robustness of
the tree an iteration of 1000 pseudoreplicates was per-
formed. DNA sequences of the tufA gene of Kornmannia
leptoderma are available from GenBank (for accession
numbers see Table 1).
Results
The first specimen was discovered in late winter (Febru-
ary) 2013. It drifted in very sheltered and shallow water at
Mönkeberg in the Kiel Fjord. Cultivation of this specimen
allowed for observation of the heteromorphic life cycle of
Kornmannia. Within 3months spores were released that
formed monostromatic disks of characteristic morphol-
ogy (Figure 2A and B). During seven more months the
crusts increased in size until they reached a diameter of
up to 1.5mm (Figure 2C). At the same time pseudoparen-
chymatous growth also increased the thickness of the
disks, in particular toward their center. A release of prop-
agules was not directly observed, but in December 2014
– 10months after the launch of the experiment – spores
or gametes had been released that germinated into small
filaments (Figure 2D). Some of these formed a new genera-
tion of disks, which gave rise to minute thalli with an erect
tubular morphology (Figure 2C and D), that were closed
at the tip. Within three more months these germlings
increased in size to a length of approximately 5mm before
they liberated their content as spores. Only the cell wall
structures remained (Figure 2E). Attached material from
Heiligenhafen Binnensee that had been collected in late
summer (August 2017) developed considerably faster.
Large numbers of tetraflagellate swarmers were immedi-
ately released from the thallus. As previously observed
with the material from Mönkeberg, germination of
attached swarmers resulted in a formation of disks, which
increased in size and thickness. After 5–6months some
of the primary disks formed saccate thalli (usually one, in
one case two, Figure 2F and G) that increased in length as
previously observed on secondary disks with the material
from Mönkeberg. At the same time biflagellate swarmers
were also released by primary disks (Figure 2H) and after
attachment they germinated into a second generation of
filaments (Figure 2F–H) that eventually formed secondary
disks.
DNA sequencing revealed that the tufA marker gene
of the first parental sample from Mönkeberg had more
than 99% identity with a reference sample of Kornmannia
leptoderma from the Canadian west coast (Saunders and
Kucera 2010). Twenty additional specimens were col-
lected until April 2015 (Table 1) at 16 different locations
along a Baltic Sea coastal section approximately 220 km
long and at Helgoland (Figure 1). They were all – based
upon fully or partially sequenced tufA marker genes –
closely related and most probably conspecific with the
specimen collected in Mönkeberg and with the reference
sample (see Figure 3 for a phylogenetic tree with selected
samples). All specimens were light green monostromatic
sheets with central or basal attachment, in most cases
with strongly ruffled margins (Figure 4). Occasionally
multiple thalli arose from the same base. Thallus lengths
of 5cm were rarely – if ever – exceeded. Cells in the basal
parts were always stretched and between 1.5 and 4.5
times longer than wide. Cells in the middle parts of thalli
were much less stretched. They exhibited diameters of
14–26 × 8–19μm and they typically clustered in groups of
two or four.
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F. Weinberger etal.: Range expansion of Kornmannia5
Figure 2:Life cycle stages of Kornmannia leptoderma, raised from material collected in Mönkeberg (A–E) and Heiligenhafen (F–H).
Primary thallus disks after (A) 3months, (B) 4months and (C) 10months, in (C) surrounded by five secondary thallus disks. (D) secondary
basal disk bearing a young erect tubular thallus on the left and newly germinated filaments on the right (after 12months). (E) primary disk
and two dead tubular thalli (after 15months). (F) and (G) primary basal disk bearing two erect tubular thallus branches of different size and
surrounded by early filamentous stages of secondary disks (5.5months). (H) biflagellate swarmer. Arrows indicate flagella in (H) and tubular
sporophytes in other images, the latter appear often blurred because images were taken with an inverted microscope through the bottom of
the culture vessel. Length of scale bars: 50 μm in (A), (B), (D), (F) and (G), 1mm in (C) and (E), 20 μm in (H).
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6F. Weinberger etal.: Range expansion of Kornmannia
Discussion
Our combination of genetic, ontogenetic and morpho-
logical observations allows for a relatively unambiguous
identification of the examined material as Kornmannia.
A unique character of the genus is its heteromorphic life
cycle that combines a discoidal or sometimes filamentous
gametophyte and an erect, first tubular, then saccate and
finally monostromatic sporophyte that emerges from an
initial discoidal stage (“Disk-sac ontogeny”; Golden and
Cole 1986). This life cycle has been described in detail
for Kornmannia leptoderma from Helgoland (Kornmann
and Sahling 1962) and Norway (Bliding 1968) and for
Kornmannia zostericola from Japan (Yamada and Kanda
1941, Tatewaki 1969) and British Columbia (Golden and
Cole 1986). Despite small variations, the life cycle traits
of both taxa appeared similar, and this was an impor-
tant argument in support of the view that the two taxa
are synonyms (Golden and Cole 1986). In our study tetra-
flagellate spores released by monostromatic thalli from
the Baltic Sea gave rise to a primary discoidal life stage
that appeared morphologically identical to the discoidal
gametophytes described by the authors mentioned above.
We also observed a release of biflagellate swarmers from
these disks, which is again in agreement with earlier
observations of biflagellate gametes in Kornmannia. We
could not directly observe a fusion of these swarmers
as described by Tatewaki (1969), but such formation of
Figure 3:Phylogenetic tree of Ulvales and Ulothrichales exhibiting monostromatic morphologies.
Maximum likelihood (ML) phylogenetic tree based on analysis of plastid tufA gene DNA partial sequences. ML bootstrap support values
≥90 are shown at each node. Branch lengths are drawn proportional to the amount of sequence change. GenBank accession numbers are
indicated before species names. Names of target samples from the Baltic Sea are in bold. Prasiola stipitata and Bryopsis corticulans were
used as outgroups.
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F. Weinberger etal.: Range expansion of Kornmannia7
zygotes probably happened, since the subsequent devel-
opment of our cultures was again in accordance with
earlier reports (Kornmann and Sahling 1962, Bliding 1968,
Tatewaki 1969, Golden and Cole 1986): the propagules
that had been released germinated into short filaments.
These filaments formed secondary disks, which gave rise
to tubular erect sporophytes that were closed at the apex,
as previously described for K. leptoderma (Kornmann and
Sahling 1962, Bliding 1968, Tatewaki 1969, Golden and
Cole 1986). We were unable to observe the final develop-
ment into monostromatic thalli because the sporophytes
released zoospores and thereby emptied their cells before
the necessary size had been reached. Nonetheless, the
observed ontogeny – including the morphological traits of
both generations – was fully in agreement with that of K.
leptoderma. Tubular germlings were observed in culture,
while monostromatic sheets were observed in nature. We
did not observe the intermediate saccate morphologies in
the Baltic Sea, but absence of saccate forms has also been
observed elsewhere (Golden and Cole 1986). In our second
experiment tubular erect sporophytes were already formed
by primary disks. Such asexual reproduction of K. lepto-
derma sporophytes has also previously been reported, for
example by Kornmann and Sahling (1962) with material
from Helgoland and by Yamada and Kanda (1941) with
material from Japan.
Further evidence for the identity of our material with
Kornmannia comes from the DNA barcoding approach. The
tufA marker gene indicated that our material is genetically
more close to the only reference sample of the genus Korn-
mannia that has so far been published than to any other
green algal genus that forms monostromatic blades. The
reference sample in question represents a specimen of K.
leptoderma from British Columbia (Saunders and Kucera
Figure 4:Sporophytes of Kornmannia leptoderma.
(A) Living specimens from Heiligenhafen-Graswarder (22.8.2014); herbarium specimens from (B) Redentin (19.7.2013), (C) Heiligenhafen
(20.7.2013, epiphytic on Fucus vesiculosus) and (D) Gollwitz (19.7.2013); natural assemblages at (E) Wulfen (27.9.2014) and (F) Redentin
(19.7.2013). Scale bars in B-D=2cm.
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8F. Weinberger etal.: Range expansion of Kornmannia
2010). Unfortunately the authors did not mention how
their specimen was recognized as K. leptoderma, possibly
it was found in the characteristic epiphytic association
with Zostera or Phyllospadix that is often observed on the
North American Pacific coast and allows for a relatively
reliable identification based upon morphological traits
(Golden and Cole 1986). Together with our samples from
the Baltic Sea and Helgoland, the reference sample of K.
leptoderma clearly formed one distinct cluster (Figure 3).
The identities between pairs of sequences within this
branch were always larger than 99.2% and often com-
plete. For example, no base pair divergence was detected
between the reference sequence from British Columbia,
two samples from Helgoland and two of the sequences
from the Baltic Sea (sites Aschau and Hohen-Wieschen-
dorf). All these specimens apparently belonged not only
to the same genus, but to the same species. Thus, our
data confirm that the same Kornmannia species is present
at Atlantic and Pacific coasts, as previously suggested
(Golden and Cole 1986). We were unable to compare our
data to DNA sequences obtained from type material, but
most probably the species is K. leptoderma, given that the
only other species described within the genus (K. zosteri-
cola) is considered as a synonym. An in-depth comparison
of the genetic structure of different Atlantic and Pacific
populations of Kornmannia might provide an answer to
the question whether the genus harbors more than one
species or not. However, this was beyond the scope of the
present work. Not only our DNA barcoding data and our
observations of the ontogenetic development, but also
our morphological observations of field-collected sporo-
phytes largely correspond with descriptions of K. lepto-
derma (Bliding 1968, Kornmann and Sahling 1983). We
therefore conclude that K. leptoderma is currently present
not only at Helgoland – where the species has not been
observed for four decades – but also in the SW Baltic Sea,
where it has not previously been recorded (Nielsen etal.
1995, Schories etal. 2009).
Interestingly, Kornmannia leptoderma from the Baltic
Sea differs from populations from Helgoland and Hok-
kaido that were investigated half a century ago by its
capacity for life cycle completion at a temperature of 15°C.
The optimal water temperature for life cycle completion
of material from Hokkaido was approximately 5°C and
gametophytes could only become fertile at temperatures
below 10–12°C (Tatewaki 1969). Also in K. leptoderma
from Helgoland a temperature of 15°C inhibited the forma-
tion of sporophytes completely and caused parthenoge-
netic multiplication and malformations of gametophytes
(Kornmann and Sahling 1962). In contrast, a continuous
temperature of 15°C could not prevent the formation of
sporophytes in our experiments and also no malforma-
tion of gametophytes was observed. Instead, the full life
cycle was completed within 15months and a parthenoge-
netic reproduction of sporophytes was observed within
5.5months, which clearly contrasts with the above men-
tioned studies.
In addition to temperature, daylength often affects
algal life cycles and this was also reported for Korn-
mannia leptoderma. At temperatures of 10°C or less and
a daylength of 16h, Golden and Cole (1986) observed for-
mation of branched filaments instead of gametophytic
disks and no reproduction of sporophytes. However, a
development of gametophytic disks and reproduction of
sporophytes already at an early stage was observed by
the same authors at a daylength of 8h. This behavior in
short day conditions was very similar to the development
of K. leptoderma from the Baltic Sea at a daylength of 12h.
We did not test the effect of long day conditions on our
material, therefore we cannot exclude that such condi-
tions would also inhibit the formation of sporophytes in
specimens from the Baltic Sea. However, we frequently
detected K. leptoderma sporophytes in summer between
July and August (Table 1), when water temperatures may
easily reach 20°C (Table 1, see also Lennartz etal. 2014)
and days are longer than 12h. This is in agreement with
our observations of life cycle completion at temperatures
above 10°C, but it contrasts with past observations by
Kornmann and Sahling (1983), who explicitly described
K. leptoderma from Helgoland as a “spring alga”. Also at
Helgoland we recently discovered sporophytes not only in
spring, but also in September, although mean sea surface
temperatures of 12°C or less occur at Helgoland only from
November to May (Table 1, see also Wiltshire etal. 2009).
Clearly, the formation of sporophytes on Helgoland and
in the SW Baltic is not restricted to spring or to the cool
season.
These field observations – together with our ontoge-
netic observations, that were obtained under temperature
controlled conditions – strongly suggest that the Baltic Sea
and Helgoland have been reached by an ecotype of Korn-
mannia leptoderma that is adapted to elevated tempera-
tures. Our attempts to isolate DNA from existing historical
samples of K. leptoderma from Helgoland so far failed. It
is for this reason currently not possible to examine the
genetic similarity between recent specimens and those
that were present in Germany half a century ago. Thus, we
are unable to decide whether recent German populations
are descendants of the Helgoland population that existed
five decades ago. Possibly this population never really
became extinct, adapted to warm summer conditions
and expanded its distribution range into the Baltic Sea,
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F. Weinberger etal.: Range expansion of Kornmannia9
which is at a distance of less than 200 km from Helgoland
through the Kiel Canal (Figure 1).
Alternatively, all recent populations in Germany
could result from introductions of more resistant individu-
als. For example, two different populations of Kornmannia
leptoderma with overlapping geographical distribution
have been distinguished in the NE Pacific (Golden and
Cole 1986). One of these (“KZ”) had a more southerly
distribution limit than the second and was not only dis-
covered in British Columbia, but also in California. This
more southern population was reportedly sometimes
sexual when adjacent stands of the second population
were asexual. The authors compared the ontogenetic
development of both populations under controlled con-
ditions at 5°C and 10°C (but not at higher temperatures)
and found no important differences. The authors there-
fore concluded that both populations probably belong to
the same species, but they nonetheless suggested that K.
leptoderma as a species might currently undergo radiation
(Golden and Cole 1986). In this light, the question obvi-
ously arises whether recent southern North Sea and Baltic
Sea populations in Germany are derived from southern
Pacific populations of K. leptoderma. Also a range expan-
sion into the Baltic Sea of populations in Northern Europe
cannot be excluded. Such a scenario would be reminiscent
of the southward range expansion by Fucus evanescens
C. Agardh into the Baltic Sea that happened approxi-
mately 25 years ago (Schueller and Peters 1994) and it
would perhaps mirror the development of southern and
northern populations of K. leptoderma in the Pacific that
was proposed by Golden and Cole (1986). However, the
genetic similarities or dissimilarities between Northern
and Southern populations on Pacific and Atlantic coasts
– as well as between the putative synonyms K. lepto-
derma and Kornmannia zostericola – have so far not been
explored, and it is for this reason not possible to decide
with certainty whether the Kornmannia populations that
are present in our study area today and that were also
reported from British Columbia by Saunders and Kucera
(2010) represent the same species as Kornmannia popula-
tions that were present in our study area 40years ago.
Interestingly, Kornmannia leptoderma was not found
on a section of nearly 100 km between the Danish border
and Kiekut (Figure 1). This observation could suggest that
K. leptoderma did not reach the German Baltic Sea area by
continuous southward migration from the Kattegat area
through the Danish Belt, but rather by long distance trans-
port, followed by a point introduction. At the same time,
the apparent absence of K. leptoderma from the northern
coastal section could indicate that its spread into the area
is incomplete and perhaps relatively recent.
Conclusion
The increased performance of Kornmannia leptoderma at
elevated temperature in the Baltic Sea suggests that its
establishment may be less transient than that of K. lep-
toderma on Helgoland 50 years ago. A synopsis of the
environmental conditions at all 16 confirmed collection
sites of K. leptoderma in the SW Baltic Sea (Table 1) sug-
gests that the species mostly occurs in locations that are
relatively protected from waves and very shallow (<50cm
below mean sea surface level). In such environments the
species typically grows on stones or epiphytically on the
bladder wrack Fucus vesiculosus L. Salinities down to at
least 10 are tolerated. Given the general adaptation of K.
leptoderma to boreal environments, its spread northward
and eastward into the Baltic Sea seems very probable, if
the species can tolerate salinities below 10 that predomi-
nate east of the Darss Sill. On the other hand, a further
spread in the southern North Sea may also be expected,
given the tolerance of this species to corresponding tem-
perature conditions.
Acknowledgments: This investigation was partially sup-
ported through a grant given by the German Academic
Exchange Service (DAAD) to DA.
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Bionotes
Florian Weinberger
Marine Ecology Division, GEOMAR
Helmholtz-Institute for Ocean Science,
D-24105Kiel, Germany
fweinberger@geomar.de
Florian Weinberger is a senior scientist at the GEOMAR Helmholtz
Centre for Ocean Research (Kiel, Germany). His research focus is
on the ecology of nuisance seaweeds, on the eco-evolutionary
implications of seaweed invasions and on the microbiological and
molecular biological aspects of seaweed and aquatic plant ecology.
Sophie Steinhagen
Marine Ecology Division, GEOMAR
Helmholtz-Institute for Ocean Science,
D-24105Kiel, Germany
Sophie Steinhagen is a PhD student at the GEOMAR Helmholtz
Centre for Ocean Research (Kiel, Germany) in the division of
Marine Ecology. She holds a Master’s degree in biology with a
focus on Marine Botany from the Justus-Liebig-University Gießen
(Germany), where she formerly investigated tertiary endosymbioses
in amoeboid microalgae of the classes Chlorarachniophyceae and
Synchromophyceae. Her current research addresses the taxonomy,
molecular phylogeny and species delimitation of green seaweeds,
particularly within the order Ulvales. She also investigates biodiver-
sity and morphologic plasticity within the genus Ulva.
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F. Weinberger etal.: Range expansion of Kornmannia11
Dmitry F. Afanasyev
Department of Hydrobiology, Azov Research
Institute for Fisheries, Rostov-on-Don
344002, Russia; and Department of Botany,
Southern Federal University, Rostov-on-Don
344006, Russia
Dmitry F. Afanasyev is head of the department of hydrobiology
at the Azov Sea Research Institute for Fisheries (Rostov-on-Don,
Russia). His research focus is on the ecology of seaweeds and sea-
grasses, phytosociology and on seaweeds and aquatic plants stock
assessment.
Rolf Karez
Landesamt für Landwirtschaft, Umwelt und
ländliche Räume des Landes Schleswig-
Holstein, Hamburger Chaussee 25, Flintbek
24220, Germany
Rolf Karez is a marine biologist with a focus on the ecology of sea-
weeds. He now works in an EPA in northern Germany as scientific
employee and is responsible for the monitoring of seaweeds and
seagrasses and the assessment of seawater quality with respect
to macroalgae. He also works with non-indigenous species in the
North and Baltic Seas.
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Florian Weinberger, Sophie Steinhagen,
Dmitry F. Afanasyev and Rolf Karez
New records from the southern North Sea
and first records from the Baltic Sea of
Kornmannia leptoderma
https://doi.org/10.1515/bot-2018-0019
Botanica Marina 2018; x(x): xxx–xxx
Research article: Combined
genetic, morphological and
ontogenetic observations show
that Kornmannia leptoderma
has expanded its distribution
range into the Baltic Sea. At
the same time the species is
again (or still) established at its
extreme southern distribution
limit in the North Sea.
Keywords: Baltic Sea;
Kornmannia; marine invader;
range expansion; Ulvales.
Graphical abstract
Botanica Marina 2018 | Volume x | Issue x
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