PT - JOURNAL ARTICLE AU - Williams, C. Rosie AU - Bees, Martin Alan TI - A tale of three taxes: photo-gyro-gravitactic bioconvection AID - 10.1242/jeb.051094 DP - 2011 Jul 15 TA - The Journal of Experimental Biology PG - 2398--2408 VI - 214 IP - 14 4099 - http://jeb.biologists.org/content/214/14/2398.short 4100 - http://jeb.biologists.org/content/214/14/2398.full SO - J. Exp. Biol.2011 Jul 15; 214 AB - The term bioconvection encapsulates the intricate patterns in concentration, due to hydrodynamic instabilities, that may arise in suspensions of non-neutrally buoyant, biased swimming microorganisms. The directional bias may be due to light (phototaxis), gravity (gravitaxis), a combination of viscous and gravitational torques (gyrotaxis) or other taxes. The aim of this study is to quantify experimentally the wavelength of the initial pattern to form from an initially well-mixed suspension of unicellular, swimming green algae as a function of concentration and illumination. As this is the first such study, it is necessary to develop a robust and meticulous methodology to achieve this end. The phototactic, gyrotactic and gravitactic alga Chlamydomonas augustae was employed, with various red or white light intensities from above or below, as the three not altogether separable taxes were probed. Whilst bioconvection was found to be unresponsive to changes in red light, intriguing trends were found for pattern wavelength as a function of white light intensity, depending critically on the orientation of the illumination. These trends are explored to help unravel the mechanisms. Furthermore, comparisons are made with theoretical predictions of initial wavelengths from a recent model of photo-gyrotaxis, encouragingly revealing good qualitative agreement. BBMBold's basal mediumCconcentrationdscaled layer depthEEkman numberFFTfast Fourier transformHlayer depthIlight intensityIccritical light intensityk0initial wavenumberkccritical wavenumberkddominant wavenumberRaRayleigh numberRaccritical Rayleigh numbert0time from mixing to pattern formationvvolumeWIimage widthα, β, cfitting parameters in the double logarithmic functionχdimensionless ratio of critical to source intensityλ0initial wavelengthυviscosity|Ω|vortex mixer speedτdirection correlation time