EXPERIMENTAL OBSERVATIONS ON THE FLOTATION OF MARINE DIATOMS. III. BACTERIASTRUM HYALINUM AND CHAETOCEROS LAUDERI

Abstract

The influence of cell age, cell size, cell shape, and mode of colony formation on the sinking rates of Bacteriastrum hyalinum Lauder and Chaetoceros lauderi Ralfs was investigated in 18 experiments. The mean sinking rate of B. hyalinum ranged from 0.39 to 1.27 m/day; the absolute minimum and maximum rates were 0.24 and 7.49 m/day. Senescent populations were generally characterized by higher sinking rates. An increase in the number of cells per chain was accompanied by an increased sinking rate.The mean sinking rate of C. lauderi ranged from 0.46 to 1.54 m/day; the absolute minimum and maximum rates were 0.25 and 6.24 m/day. Culture age did not appear to influence the sinking rates. Chains of post‐auxospore cells generally sank faster than pre‐auxospore cells, probably partly attributable to the lower cell surface area: cell volume ratio of the post‐auxospore cells. As with B. hyalinum, an increased sinking rate accompanied an increase in the number of cells per chain. This direct relationship between chain size and sinking rate does not appear to be due solely to the associated decrease in chain surface area : chain volume ratio; but may be also influenced by other unknown factors. Post‐auxospore cells of C. lauderi did not exhibit the positive buoyant movements described previously for Rhizosolenia setigera.From 13 to 16 days would be required by the species to sink 100 m at the absolute maximum sinking rates observed, while from 455 to 475 days would be required at the absolute minimum rates. The data suggest that during active growth an increased buoyancy independent of the species’ morphological characteristics occurs. Changes in the ratio of pigment absorbance at 434 : 474 mµ and 382 : 352 mµ in B. hyalinum, and 382 : 474 mµ in C. lauderi suggest that physiological changes that may have influenced the observed sinking rate characteristics were occurring with culture age.