Diatom of the month – July 2016: Nitzschia amphibia

by Luca Marazzi*

Nitzschia amphibia belongs to the nitzschioid group: its valves are symmetrical to both apical and transapical axes, and taper to bluntly rounded apices; the raphe is well developed near the valve margin, and enclosed within a canal¹. The original description was made by Albert Grunow in 1852, when the US President was Millard Fillmore, the last one not to be affiliated with either the Democratic or Republican party. This is how ‘old’ are some of the species names of algae and other organisms that persist to this day, while new species are continuously described at an increasing rate. Grunow was one of the eight most ‘profilic’ algal taxonomists who described more than 1,000 species during their career, the others being Kützing, Gottfried, Hustedt, Agardh, Harvey, who worked in the 1800s, and Lange-Bertalot (the only one still alive and active) and Skvortsov in the 1900s².

Fig. 1. a) Nitzschia amphibia in valve view and girdle view (scalebar = 10 µm) (photos by Pat Kociolek); b) Florida Coastal Everglades LTER program diatom image database.

While the number of algal taxa discovered per taxonomist is increasing, the number of taxonomists is going down (Fig. 2), not a good sign on the already difficult road to a deeper understanding of thousands of species of algae and their ecology. New molecular and genetic techniques imply that doubtful / uncertain species (from a traditional taxonomy viewpoint) are increasingly called ‘clade’ (a grouping that includes a common ancestor and all the descendants, living and extinct, of that ancestor), ‘specimens’ (a single example of a collected alga) or ‘strains’ (a genetic variant or subtype). This creates the further challenge of integrating historical collections into such modern laboratory research² to provide continuity, whilst improving the accuracy of such discoveries.

  

 

Fig. 2. The number of algal species described by each taxonomist keeps increasing while the number of specialized taxonomists is decreasing (source: Clerk et al., 2013).

So the algal taxonomy road, and this blog post, do lead somewhere²…here let’s zoom back on this month’s diatom. Nitzschia amphibia is a glass-encased moderately motile alga that likes muddy aquatic habitats, and is an indicator of phosphorus enrichment (>800 µg g^-1 in Everglades periphyton), alongside other diatoms such as Gomphonema parvulum, Eunotia incisa, Rhopalodia gibba, and the green alga Mougeotia (which has a carbohydrate cell wall, not a silica one like diatoms)³. In general, Nitzschia species not only glide horizontally in epipelic habitats (mud), but also vertically through the substrates, and, together with stalk-forming diatoms like G. parvulum support the formation of complex three dimensional biofilms. Such 3D communities abound in the Everglades (Fig. 2), and other freshwater ecosystems, for example in Lake Sakadaš, in the Croatian part of the Danubian floodplain⁴, and along the River Team in Northern England, where Martyn Kelly studies, but also draws (and tells stories about) how various species attach to plants and other algae (Fig. 3). His work is another example of the successful and important marriage between science and art that we are experiencing!

  

 Fig. 3. A periphyton sampling site in Shark River Slough (SRS-1d) where Nitzschia amphibia can be found (photo: Franco Tobias, April 2008).

Fig. 4. Three dimensional biofilms from the River Team (Northern England) as depicted by British diatom scholar and artist Martyn Kelly; river bed with the filamentous green alga Cladophora and numerous attached diatoms such as Craticula, Navicula, and Nitzschia (circled in red). Source: Kelly (2011) “Of microscopes and monsters - Journeys through the hidden world of Britain’s freshwaters” - http://www.martynkelly.co.uk/).

* Postdoctoral Associate in Dr. Evelyn Gaiser's lab at Florida International University.

       1. Source: http://westerndiatoms.colorado.edu/taxa/morphology/nitzschioid

      2. De Clerck O.D., Guiry M.D., Leliaert F., Samyn Y., Verbruggen H. (2013) Algal taxonomy: a road to nowhere?

          Journal of Phycology, 49: 215–225.

      3. Gaiser E.E., McCormick P.V., Hagerthey S.E. & Gottlieb A.D. (2011) Landscape Patterns of Periphyton in the

          Florida Everglades, Critical Reviews in Environmental Science and Technology, 41(S1), 92–120.

      4.   Žuna Pfeiffer T., Mihaljević M., Špoljarić D., Stević F. & Plenković-Moraj A. (2013) The disturbance-driven

          changes of periphytic algal communities in a Danubian floodplain lake. Knowledge and Management of

          Aquatic Ecosystems (2015) 416, 02.