Below the Kolmogorov scale: the non-turbulent sex life of phytoplankton

Abstract

Below the Kolmogorov length scale there is no turbulence and phytoplankton gametes swim in order to encounter each other and achieve syngamy. An encounter rate model, Z = π √2 R² u N, is derived incorporating cell size (R), swimming speed (u) and cell concentration (N). Assuming Z = 1 day⁻¹, calculations using this model show that inside a 'Kolmogoroveddy' abundances range from 10⁷ cells m⁻³ to 10¹¹ cells m⁻³ for large (38μm) to small (2μm) gametes respectively, which is of the order of the numbers observed in algal blooms and in thin layers. Furthermore, cell density-dependent gamete formation, a hypothetical case of quorum sensing, could be expected at 2–4 × 10⁸ cells m⁻³. The calculations presented here not only show that phytoplankton need 'bloom' concentrations for a swiftly functioning sexual cycle, but they may also be helpful in designing experiments to test life-cycle hypotheses.