Diatoms: a freshwater curiosity

Imagine an organism that takes on a bewildering array of beautiful and complex forms and is common to almost all aquatic ecosystems, yet is invisible to the naked eye.  Organisms that have existed since the Jurassic period yet are being intensively researched by scientists looking for new breakthroughs in computer chip technology.   Look beneath the surface and discover the incredible diatom…

Asterionella formosa (Image: wikipedia)

Diatoms are a widespread group of algae that can be found almost anywhere there is water across the world.  With known records extending back over 180 million years ago, there are now thought to be over 100,000 species of diatoms globally, exhibiting an incredible variety of unusual and beautiful forms.

Diatom image from "Water Lives..." showing Gomphonema acuminatum var. coronatum animated by Adam Proctor (fortsunlight.co.uk)

For such a tiny organism, diatoms are incredibly important .  In freshwaters, diatoms are at the bottom of the food chain, and they are exceptionally sensitive indicators of water quality.  Tiny diatoms also provide a window into the past: as millions of individuals die and fall to the bottom of the lake they leave their fossil remains in the mud which carry clues to environmental history.  Living diatoms have very particular preferences for environmental conditions such as water pH, nutrient levels and water salinity.  This means that by examining the diatoms preserved in the layers of mud, scientists can ‘reconstruct’ past environmental conditions, information that is very useful for modern day environmental managers.  You can read more about this historical diatom detective work here.

Fragiliaria crotonensis (image: http://craticula.ncl.ac.uk)

New research in the semi-conductor industry is seeking to learn from the dense, complex shapes formed in the diatom silica shell as a means of designing faster computer chips.  Similarly, research is also being carried out on the lightweight but incredibly strong diatom cell structures by the aerospace and car industries, hoping to gain insights for designing new products.  You can read more about both these exciting research projects here.

Diatom image showing Fragiliaria crotonensis and Asterionella formosa from "Water Lives..." animated by Adam Proctor (fortsunlight.co.uk)

The range of complex diatom forms has fascinated scientists and amateur naturalists since the invention of the microscope, and provided abundant inspiration for our “Water Lives…” animation.  It was popular in Victorian England to mount kaleidoscopic arrays of diatoms on slides, adding another layer of glass to the organism’s fascinating display. Diatoms have also inspired artworks such as Ernst Haeckel’s 1904 Artforms of Nature, Liz Douglas’ “Mire” series of paintings, Klaus Kemp’s slide mounts and David Mann’s series of etchings and mezzotints.  A recent art-science collaboration between Dr Paul Hargreaves and Fay Darling brought the diatoms to life in a dazzling array of shapes and colours through the “colourising” of a set of scanning electron micrographs of the organisms.

Example of the stunning art-science collaboration work on diatoms by Fay Douglas and Dr Paul Hargreaves. Image: Fay Douglas and Dr Paul Hargreaves (http://www.flickr.com/photos/galfaye/)

Many diatoms are pelagic, which means they spend their lives suspended in open water, living a ‘boom and bust’ life-cycle where population numbers wildly fluctuate depending on the amount of light and nutrients available from season to season. All diatoms have the same basic form, a single cell (either “centric” with a radial symmetry or “pennate” diatoms with a long axis symmetry) within a silica shell, called a frustule, generally between 0.005 and 0.2 millimetres in size (but can be up to a “gigantic” 1mm).  Diatom frustules fit together in two slightly overlapping valves like a hat box or Camembert case.

Cocconeis molesta var. crucifera. (Image: UCL, http://www.ucl.ac.uk/GeolSci/micropal/diatom.html)

Silica is used (amongst many other things) to make glass.  It could be said that diatoms live their entire life in glass houses – natural display cabinets for their amazing forms.  Diatoms divide to create two smaller daughter cells, each taking one half of the parent cell.  This means that as diatom populations grow, the average size of each individual decreases (up to a point where sexual reproduction takes place to produce a new full size  cell before the whole process repeats itself– imagine if that were true in humans!

Many thanks to Dr Rick Battarbee (BioFresh, University College London) and Dr Alistair Seddon (Long-term Ecology Laboratory in Department of Zoology, Oxford) for their input, advice and corrections on this article.

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