The Silent World

Why silent plankton: I took the words Silent Plankton from the title track of Akira Sakata’s beautiful jazz CD .  jazz musician and composer of international standing , he is a trained fisheries biologist; the name of his regular group Harpacticoida will raise a smile with some.  Akira was born in Kure city, Hiroshima on February 21th 1945 – he would have been just 6 months old on the 6th of August of that year when the atomic bomb was exploded over Hiroshima. Although Kure  is some 20 or so km from the centre of Hiroshima, it surely is a very sobering thought.  He studied marine biology at Hiroshima University and specialised as a fisheries biologist; plankton, as the food of fish, will have featured very prominently in his training and science.  The words silent plankton are particularly perceptive as it gives us an important insight into the very special world of these wonderful creatures, far away from our own experience and we’re now going to go down and find out what it is like there.

Down there with the bugs: the smaller forms on the ocean plankton live on a scale (1/100^th to 1/000^th of a millimetre) that most of us lack an intuitive feel for. Perhaps not a spooky as the quantum world but well along the way.   When you look at particle movements on the microscopic scale they behave as if the water was viscous, movements are slow and soon damped out.   It is often said that it would be like swimming in molasses or honey.   This is a rather misleading way of looking at it, as the viscosity of water is the same on our scale as on theirs – it’s primarily about momentum rather than viscosity.  A better way to understand it is to try to throw a balloon across the room - try it and it will drive you nuts.   No matter how hard you try it will stop in a meter or so.  The moving balloon have very little momentum and this runs out almost as soon as   it leaves your hand.   Fill the balloon up with water and it’s a totally different story – it will fly across the room to devastating effect when it hits the wall on the other side – not recommended as an experiment!  

Supersonic bacteria : Here’s an example how things are down on their scale:  bacteria swim at a greater relative speed than a jumbo jet – about 30 or so body lengths/sec, sadly the poor old jumbo can only bimble along at about 3-4 fuselage lengths/second.   To achieve this pathetic performance it consumes about 0.5 watts/gm, where as our bacterium rips along at ten times the relative speed, consuming just a mere 0.0005 watts/gm in water, a much more viscous medium, with a propulsion system, a simple flagellum, that was designed a billion or more years ago.   We’ve got a long way to go to catch up nature, if we ever will .  

When a bacterium stops swimming is coasts for just 0.1 Angstrom and stops within less than one microsecond.  The distance between atoms in a molecule is ~1 Angstrom (1/10,000,000^th of a millimetre), so a bacterium coasts for a small fraction of the length of a hydrogen to hydrogen bond – it would be like stopping a Formula One car in 1/10^th of a millimetre – driving full belt into a concrete block – to say the least a very nasty experience, but it doesn’t seem to bother the bacterium. 

If you want to read about this strange world have a look at the great article by E. M. Purcell, he has some fascinating tales to tell about life and times down there.  You’ll learn how if you want to get about down there, it would be wise to take a corkscrew with you, not a paddle, an oar might be useful but only if it had a flexible shaft.  You will discover that the microbial world is a bit like Alice’s journey with the Red Queen, where it was difficult to move away from your environment, and, all in all, it’s better to sit down and do nothing and your next meal will make its way to you – great news!   

Fine, but how come the silent world ? Momentum is a very feeble force down on the microscale, vibrations – the basis of sound – die out almost instantly, thus there is no sound, hence the silent world.  There is a more important side to this tale for us and even more so for the micro-critters – no momentum means no turbulence – turbulence on our scale can be a devastating force.  Think of the punishment the wind deals out on a tree in a gale.  A sail will flog itself to shreds if left unsheeted in a storm.  On our scale Nature has to contend with this, plus also the need to provide support against the continual pull of gravity – both limits the designs open to evolution.  Energy and material has to be invested in bones, tree trunks and massive muscular structures to move these hulks and keep them together.  Just removing gravity alone is a massive gain – to propel a 100 tonne whale at 20 mph requires just 10 horse power.  The evolution of shapes and forms down on microorganisms, released from these constraints of gravity and turbulence, leaves them free to produce elaborate and to us often alien structures.  It is this uninhibited variety and novelty of form that has captivated the imagination of artists and the curiosity of scientists alike.  We come back to Ernst Haeckel’s compelling observation that “Nature has created a wealth of wondrous forms whose beauty and diversity way exceed anything that has been created by man” , and perhaps her best examples may seen in the silent world of the plankton.

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