Berkeleya rutilans,
A tube dweller from tidal flats
By René van Wezel
Fragile seaweed
We usually associate a diatom with a
solitary plant cell, which cannot be seen
without a microscope. Perhaps because
we do see them mainly as a single
siliceous entity, beautifully prepared on a
slide. That they can also be visible to the
naked eye as a seaweed, no, that doesn’t
come to mind easily. Although the
alternative dutch name kiezelwier (‘silica
weed’) could be a giveaway. In any case, in
nature it can be useful to gather in
One of the advantages of microscopy
as a hobby is that once a sample is
collected, it can provide a lot of
numbers in a filament or a tube. For
example for protection against grazing, as
pleasure for a long time. As was this
find, carefully scooped into a tube by
it is euphemistically called: just imagine
having such a beautiful figure and being
Wim van Egmond during our
excursion last July. A very delicate
grazed by a barbarian of a ciliate. But it
can also be a way of clinging on to
seaweed, floating in a gully of a tidal
flat near Lauwersoog. Wim was sure
something, which can be a useful feature
in an emptying mudflat.
of it, this was a diatom!
Some detached cells, the leftmost is lying on the girdle side, and the other two (oval) are seen from above (valve view).
The choroplast plates in Berkeleya rutilans typically lie against the girdle side. Objective 40x/0.95
Berkeleya rutilans lives in tightly packed tubes
Traffic jam under the lens
Unfortunately, by doing so you also wash
Intricately thin tubes filled with glassy
away information that can be of
importance, such as the shape and position
cells, chloroplast pairs that move back and
forth through the tubes in a continuous
of the chloroplasts. In Berkeleya rutilans the
chloroplasts are in the shape of plates that
motion, like cars in a live traffic jam. What
a privilege it is to be able to witness that!
lie against the girdle. On the side (in girdle
view) it is also easy to see how the nucleus
Even if you sit behind a microscope every
day, it still is a very special moment to get
lies between the two chloroplasts.
something this clearly alive under your
lens.
Macro shot of the tubular weed, dried and spread out on
a herbarium card
There is however not much visible of the
glassy skeletons in live view. The shape of
the valves, that's about it. That is why
diatoms are often cleaned from their
organic content to be able to study them
properly as a silica skeleton on a glass
slide.
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Glass skeletons
With the electron microscope, the finest
Diatom skeletons consists of two valves: a
details of the diatom skeleton becomes
visible. The spaces between the silica ribs
lid and a box. From above, the box shape is
oval. This is called the valve view. But often
are filled with pores, and the raphe slit
appears to have gracefully formed end
the cell falls on its side, and then it looks
like a rectangle. This way, you look at the
nodes.
The most striking difference between
girdle, which glues the lid and the box
together. The structure of the valves of this
light and electron microscopy imaging is
that with a light microscope, you can look
species is not visible in the living state, but
can be seen in a diatom preparation.
right through a diatom. After all, the
skeleton is made from a kind of glassy
Embedded in a highly refractive resin,
details of the valves are becoming clear
material. A scanning electron microscope
however, purely shows the surface of the
with rows of silica ribs and a typical central
raphe with thick silica edges. Compared to
Bright field microscopy can also
reveal much of the structure of this
diatom, provided the contrast of the
camera is considerably increased
valves. Which can be either the outside,
or the inside of the valve. Depending on
most diatoms, this species appears not
neatly constructed, but slightly
looking at the inside or the outside, the
image can look very different.
asymmetrical along the length of the valve.
Marine tube dwellers
Tube forming diatoms are generally found
close to the coast, and in high abundance.
In fact they often make up the main part of
Cleaned diatom valves at maximum resolving power in the light microscope:
interference contrast with objective 100x/1.35 and water immersed condenser at NA 1.2
the ecosystem referred to as
microphytobenthos, which is the small
plant component of benthic life. Only close
to the coastline there is enough light
reaching the sea floor where the algae
lives. In such a dynamic environment
however, it is important to be able to
remain somehow in the same place.
Scanning electron microscopy image of a valve of Berkeleya
rutilans. The hairpin on the lower left is one of the girdle
elements connecting the two valves by which it forms a
whole cell (frustule).
Because once you are washed away, there
might be little chance of finding another
favorable spot to live. This is not to say that
tube dwelling diatoms always occur in a
tube. Very many specimens of tube
diatoms are found solitary, as they are
washed out from old or broken tubes. In a
favorable spot, each cell is able to form
again its own tube.
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He described it from the Wadden Sea near
Over the next decade, during the time that
Wilhelmshaven. However, the genus name
Berkeleya was not coined until 1827 by
the optical microscope was being perfected,
Per Teodor Cleve seized upon this similarity
Greville, for the species Berkeleya fragilis.
Nevertheless, the characteristics of the cells
to transfer the Berkeleya species to
Amphipleura. At the same time, slowly but
were so minute, and the optics of the time of
such crudeness, that for more than 50 years
surely, all other species of tube diatoms
found their place within the already existing
classification was solely based on colony
structure. In other words, tube diatoms were
genera. The tube diatom no longer existed
as such: it had become a category, such as a
considered a natural group. The famous
scientist Christian Gottfried Ehrenberg took it
tree or a herb.
Paradoxically, a hundred years on, the
to the extreme in 1838 by generating a single
genus (Naunema) for all tubular diatoms!
transfer of species from Berkeleya to
Amphipleura proved just one step too far.
In the following decades however, the
microscope matured. Researchers began to
On the basis of electron microscopic
examination by Cox (1975), the marine
realize that the diatoms they found in tubes
were very similar to already described species
species of Amphipleura were transferred
back to Berkeleya, the genus with which it
in completely different genera and families!
Albert Grunow, undoubtedly somewhat
all began 200 years before.
downhearted, observed this at the time and
wrote: 'Alle unsere Gattungen sind mehr oder
The first published image of this species
(as Bangia rutilans) by Lyngbye in 1819(!)
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weniger künstlich und haben nur insofern
Wert, als sie uns die Überblick über die
organischen Gebilder erleichtern' (Grunow,
1880). In English: 'All our genera are more or
less artificial and have value only insofar as
they facilitate our overview of the organic
Diatom valves can be seen from the inside or from the
outside. The differences between them can be highlighted
with a different method of electron detection. The effect
looks surprisingly similar to interference contrast for light
microscopy
In Berkeleya rutilans, differences between the inside and outside of the valves are mainly seen in the raphe slit. It ends
in a lip-shaped protrusion on the inside (the so-called rimoportula); on the outside it stops earlier and ends in a node
[living] structures'. He thereupon split the
whole group of tube diatoms into two: the old
genus Berkeleya, which he reserved for those
species with characteristics of the genus
Tubular diatoms were described already early
Amphipleura; all other species were included in
the genus Schizonema. The genus Amphipleura
in the 19th century, mainly because of the
macroscopic growth form that was
is well known from the species A. pellucida,
which enjoys the status of microscopic test
reminiscent of that of brown algae. Berkeleya
rutilans was even described as early as 1806,
object for resolution. Compared with
Amphipleura, Berkeleya species look very
at the time as Conferva rutilans ("red mash")
by Trentepohl (in Roth, 1806).
similar due to the typical forked raphe
structure.
Early descriptions!
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Will this be the end of shifting species around
to believe a single species would be able to
within the classification system? Probably not.
Berkeleya rutilans is a common species, found
survive and thrive in such different and harsh
environmental conditions. This appears true:
throughout the world. It can withstand
transitions from freshwater to marine and is
based on genetic research, the species along
the American and Canadian coasts alone can
therefore at home in the Wadden Sea, where
mudflats run dry on daily basis and rainfall can
be divided into 14 groups (Hamsher &
Saunders, 2014). Time will tell if and when
locally greatly dilute the saltyness. It’s hard
these groups will be given their own names.
Literature and links
• Cox, E.J. (1975). Further studies on the genus Berkeleya Grev. British Phycological Journal
10: 205-217.
• Grunow, A. (1880). Vorlaufige Bemerkungen zu einer systematischen Anordung der
Schizonema- und Berkeleya-Arten, mit Bezug auf die in Van Heurck's Diatomeenflora von
Belgien veröffentlichten Abbildungen der Frusteln auf Taf. XV, XVI und XVII. Part II.
Botanisches Centralblatt 4(48): 1585-1598.
• Hamsher, S.E. & Saunders, G.W. (2014). A floristic survey of marine tube-forming diatoms
reveals unexpected diversity and extensive co-habitation among genetic lines of the
Berkeleya rutilans complex (Bacillariophyceae). European Journal of Phycology 49(1):
47-59.
• Lyngbye, H.C. (1819). Tentamen hydrophytologiae danicae. Hafniae [Copenhagen]: typis
Schultzianis, in commissis Librariae Gyldendaliae.
• Roth, A.G. (1806). Catalecta botanica quibus plantae novae et minus cognitae describuntur
atque illustrantur. Fasciculus tertius cum tabulis aenaeis XII. pp. [i-viii], [1]-350, [1-2, index
pi.], [1-6, index] [1, err.], pls I-XII. Lipsiae [Leipzig]: in Bibliopolio Io. Fr. Gleditschiano.
• For a good introduction into Dutch tube diatoms, see
Pieter Houpt (1994). Marine tube-dwelling diatoms and their occurrence in the Netherlands. Netherlands Journal of Aquatic Ecology (1994) 28: 77-84. Downloadable from
https://eurekamag.com/pdf/008/008992982.pdf
Photographs were taken with the microscopical facilities of the Hydrobiological Laboratory of the
Department of Waterways and Public Works of the Netherlands, which is greatly appreciated.
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