Specific algal recoveries from sediment traps of two different designs and from mud surface deposits of large experimental enclosures (Lund Tubes) were monitored during 1978 and are analyzed in relation to the vertical and temporal distribution of ten dominant phytoplankton populations. Sedimentation accounts for differing proportions of the total loss of biomass for different algae: between 28 and 100% of diatoms; 15–95% of Eudorina ; Ankyra, Chromulina, Cryptomonas ). Rates of diatom loss are also derived from the comparison of net rates of change (k n ) and the silica uptake-derived growth rate (k 1 ); intrinsic sinking behaviour may be specifically regulated in relation to growth conditions. Implications in the calculation of sedimentary losses and their impact upon the seasonal periodicity of phytoplankton are briefly discussed.