Diatom of the month - January 2016: Gomphonema parvulum
by Luca Marazzi*
‘Who’
is it?
The genus Gomphonema includes numerous species growing on mucilaginous stalks. These
diatoms are asymmetrical biraphid, as the bottom
part is usually longer and thinner than the top part and they have two raphes, narrow
slits that allow them to move over surfaces. Yes, there are diatoms that perform photosynthesis, move
and even eat
organic matter! G.
parvulum is on the lower end of the size spectrum for the genus (length
from 15 to over 100 µm and width between 5 and 15 µm).
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Where
does it live?
In North America, species of Gomphonema can be found in
many habitat types in lakes and streams with pH close to 7. Gomphonema parvulum is widespread and tends to live in
freshwater with high nutrient concentrations. Therefore it has been widely used
as an indicator of eutrophication, including in the Everglades where
agricultural fertilization has historically increased phosphorus levels1 the reduction of
which is part of the largest wetland restoration programme
in the world. It
has a cosmopolitan distribution, but different geographical regions have been shown to
host different clades of G. parvulum from Mexico, the Faroe Islands,
Germany and Korea: Gomphonema parvulum sensu strictu, G. saprophilum, G. lagenula,
G. narodoense2. Increasing
evidence is showing that this and other species of diatoms have evolved in
relation to climate, geography and water quality so that truly cosmopolitan
taxa may be less common than previously thought.
Why
are we studying it?
In the Everglades, G. parvulum is a dominant taxa, particularly in freshwater
marshes; FIU’s Franco Tobias, Evelyn Gaiser and collaborators analyzed samples
from 237 sites to suggest revisions of its taxonomy and clarify confusion
that often arises in such a complicated, and at times subjective, discipline. They
identified 20 taxa of Gomphonema parvulum-like
diatoms from the Everglades; so far no new species have been found. This might
be due to the Everglades being a ‘teenager’ wetland (about 5,000 years old) and
very calcareous so that only a subset of this genus preferring acidic pH are
selected3. But we have a lot
of data and samples that may tell us some new ecological ‘secrets’ about
Everglades diatoms - so stay tuned with the Gaiser lab!
What can you do?
If you are a Floridian or a U.S.-American, get familiar with the diatoms of the Everglades, it is your
wetland! If you are not from this part of the world and you ever come to Miami
for its beaches, you must also go visit this fantastic ecosystem that is increasingly threatened by sea level rise. To convince yourself, please visit
the Florida Coastal Everglades Long Term Ecological Research Network website and look up for
wonderful pictures of our diatoms and the precious environments
they live in, from the ‘sweet-water' marshes to the
salty-water mangroves and
more!
Shark River Slough
- airboat morning. Photo by Franco Tobias (27 September 2011).
Tributary of the Shark River. Photo by Stephen Davis (26 June 2014)
1. Gaiser E.E., Childers D.L., Jones R.D.,
Richards J.H., Scinto L.J., and Trexler J.C. (2006). Periphyton responses to
eutrophication in the Florida Everglades: Cross-system patterns Eutrophication
today 355 of structural and compositional change. Limnology and Oceanography
51: 617–630
2. Abarca N., Enke N., Zimmermann J., Jahn R. (2014) Does the cosmopolitan diatom Gomphonema parvulum (Kützing) Kützing have a biogeography? PLOS One 9: e86885. doi: 10.1371/journal.pone.0086885
3. Tobias F.C.A.
and Gaiser E.E. 2006. Taxonomy and distribution of taxa in the genus Gomphonema from the Florida Everglades,
U.S.A. Diatom Research 21: 379-405.
2. Abarca N., Enke N., Zimmermann J., Jahn R. (2014) Does the cosmopolitan diatom Gomphonema parvulum (Kützing) Kützing have a biogeography? PLOS One 9: e86885. doi: 10.1371/journal.pone.0086885
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