When you look upon a riverbed it can seem pretty drab, lifeless and uninteresting. But if you could take a pebble in your hand and somehow magnify its surface so that the microbes that covered it were visible, you may well be surprised by the beauty of what you saw. For throughout the slimy layer of life that covers the pebble you will find diatoms, a very pretty type of algae.
Like most plants and algae diatoms photosynthesise, deriving their energy from sunlight. They differ however in that they have yellow-brown rather than green chloroplasts, which contributes to the general brownish colour of riverbeds. The slimy layer in which most river diatoms make their home is known as a biofilm. This film coats most surfaces in rivers and lakes, and is comprised not only of diatoms but also a myriad of other microorganisms such as bacteria, protists, fungi and worms. Numerous invertebrate species such as certain mayfly larvae and freshwater snails graze upon biofilms, and are in turn prey for predators such as brown trout or dippers.
Diatoms are not restricted to freshwater ecosystems, and are in fact very widespread. Vast quantities float as plankton in the ocean. However they don’t necessarily need much water, and will live wherever there are moist soils or damp surfaces. There are an estimated 100,000 species worldwide.
Two plates of diatoms from Ernsrt Haeckel’s Kunstformen der Natur (Art Forms of Nature; 1904)
While diatoms are very abundant, they have an uncommon beauty. They come in a wide variety of symmetrical forms and have ornate and patterned cell walls. This is why they became a popular subject of study for those who pioneered the use of early microscopes. Their striking appearance led to their inclusion in Ernst Haeckel’s Kunstformen der Natur (Art Forms of Nature; 1904), a book that displays a collection of the famous biologist’s most beautiful drawings and watercolours.
One of Dr Dave Chandler’s diatoms taken from his laboratory experiments (false colour image).
There is also a more mundane reason to study diatoms. Their communities change in response to human impacts such as pollution, as some species are more able to withstand contaminated waters than others. Environmentalists can therefore collect diatoms from a river and compare what species they have found to what should be growing if there wasn’t any pollution. The difference in the diatom community then gives us a good clue as to how polluted the river is. Dr Dave Chandler investigated the impact detergents had on diatom communities during his PhD at the University of Sheffield. During his research he took pictures of the diatoms he kept in his experiments, not because he needed to for his studies, but simply because they made such beautiful subjects.
Another of Dr Dave Chandler’s diatoms (false colour image).