I am an amateur naturalist trying to learn a little about everything living in my garden.
Recently, in the interests of finding some life-form with which to entertain the legions of avid readers of this blog (hem, hem), I decided to investigate what life might exist in a small pool of rainwater that had collected in the crevices of a sheet of polythene lying in my garden. Putting a drop under my hobbyist's microscope I was immediately confronted by large numbers of the creature seen in photo 1 (scale:1 small division = 1um). Some were motionless. More excitingly, others were highly active, 'zooming' through the water at a rate of knots (see later)
Some internet searching later, and with the help of photo's such as those on Ralf Wagner's microscopy site, and I'm tolerably confident I'm looking at a Heamatoccus alga.
The red colouration, motile behaviour and the presence of the transparent, gelatinous envelope surrounding the central green body all fit with the the species being H. pluvialis on this site ('Algaebase') . I don't claim any certainty over this identification however, since firstly I'm no expert, and secondly the same site lists 5 other species in the Haematoccus genus and a staggering 123,336 species of algae overall.
The family Haematoccae is part of the Volvocales order of algae, one example of which - Volvox - is a perennial favourite with microscopists. The Volvocales are equipped with two whip-like flagella - the secret to their ability to 'swim' through the water. The length and positioning of any flagella on an alga is an important aid to identification. Unfortunately the quality of my camera/microscope optics doesn't appear to be good enough to have caught these in the (dormant) Haematoccus specimen in photo 1 (or is it that flagella are lost in the dormant state?) - but the superb photo's by Wim van Egmond here show them clearly.
In researching the life in my garden I constantly come across what I imagine at first to be 'obscure' creatures. "Beyond naming it, surely no-one can have found the time to learn anything interesting or remarkable about this little critter!" I think to myself. It's a constant source of enjoyment to me to learn I'm wrong, and that for just about anything I come across, someone somewhere will have discovered some remarkable or interesting 'story' (which isn't to say that vast amounts don't remain unknown about the natural world of course).
So it was with H. pluvialis. Beyond a few dry descriptions in an obscure journal, surely there would be nothing say? Wrong again! It turns out H.pluvialis is an algae of significant commercial importance. It produces the highest known concentrations of astaxanthin of any living creature and is cultured on a commercial scale. Astaxanthins are chemicals used in the cosmetics, food and feed industries. They are antioxidants and have been studied for their potentially beneficial effects against everything from cataracts to colonic cancer. Guerin et.al. have produced a review (Trends in Biotechnology, 21(5), 2003). Astaxanthins are cartotinoid chemicals responsible for the red coloration in photo 1. They act as a 'sun block' against harmful UV rays. Those dormant algae I observed in my microscope sample seemed to contain more red pigment than mobile ones. I assume this is because dormancy is, in part, a mechanism to survive in dry conditions when cells can expect to need more protection from the sun.
Algae introducing astaxathanins into the food chain is the reason why animals higher up like shrimps, salmon and flamingos end up with pink flesh or feathers.
Returning to the issue of the mobility of H.pluvialis, Burchardt et.al (Biodiv. Res. Conserv. 1-2, 163-166, 2006) give a figure for their swimming speed of 200m/h. Given that their size is about 20um, scaling this up, and assuming a human about ~2m tall and I've got my maths right, this corresponds to a person swimming along at 20,000 km/h!
Finally, I can't end without mentioning one of the few books I have that gives a fairly detailed introductory guide to freshwater algae, namely Freshwater Microscopy by W.J. Garnett. Though it contains no real information about Haematoccus beyond a mention, it covers many common UK species in some detail. First published in 1953, I particularly like dipping into it for its evocation of a seemingly quieter more 'holistic' (for want of a better word) world, before out-of-town shopping centres and a life of frenzied commuting up-and-down packed motorways, when armies of amateur hobbyists seemed to spend their evenings and weekends learning the art of painting watercolour landscapes, investigating the geology of their county, or studying the lifeforms in their village pond. Or perhaps that's rose-tinted nonsense, though I do wonder how many hobbyists there are today, who, of a typical weekend, boil hay in rainwater in order to culture pond protozoa for study as Mr Garnet advises!
On the other hand I may be entirely wrong and there are legions of you hay-boilers out there! If you're one such, do leave a message to say hello.