SPECIFIC VARIABILITY IN FE-ENRICHED CULTURES FROM THE EQUATORIAL PACIFIC

Water collected on the spring equatorial Pacific Joint Global Ocean Flux Study (JGOFS) was placed in ultra-clean bottles in an incubator on deck under the direction of the team of J.H.Martin. Half of the bottles were enriched with 2.53 mM iron; the other half served as controls. Cell counts increased, while the number of species was reduced. in both the controls and the treated samples over the period of the experiment. Diatoms dominated. and after an early growth spurt in the Fe-enriched bottles, most diatom species showed greater growth in the controls at the end of the 6 day experiment. However, as the experiment was terminated, more cells overall were noted in the Fe-enriched samples, with the most abundant diatom. Cylindrotheca closterium, principally responsible for the difference. Growth rates were high in both the controls and the treated samples, with overall rates of 1.3-3.0 divisions day-1 in the Fe-treated samples and 1.9-3.4 divisions day-1 in the controls. The group of smaller pennate diatoms averaged 2.9 divisions day-1 in the Fe-treated samples and 3.3 divisions day-1 in the controls over the entire experiment.