Graduate Thesis Or Dissertation
 

Some effects of ultraviolet-B radiation (290-320 nm) on unialgal and mixed cultures of two centric diatoms

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  • Reduction of stratospheric ozone caused by human perturbation with halocarbon compounds and the consequent increase in mid-wavelength ultraviolet radiation (UV-B radiation. 290-320 nm) reaching the earth's surface could have deleterious ecological effects on marine primary producers. Unialgal and mixed cultures of Thalassiosira pseudonana and Thalassiosira weisflogii were exposed to three levels of UV-B radiation (1.26 Wm⁻², 1.58 Wm⁻², and 0.02 Wm⁻²) in three experiments, each of four day duration. The effects of these three levels of UV-B irradiance on cell numbers, doubling times, and relative biomass were analyzed. Two analyses were done: a two-treatment (UV-B/no UV-B) and a three-treatment (UV-B intermediate/UV-B enhanced/no UV-B) analysis. Results of the two-treatment study show that UV-B radiation depresses population growth of the two diatoms. An apparent competitive shift in favor of the larger, less UV-sensitive diatom (Thalassiosira weisflogii) was also noted, although it was not statistically significant (p>0.05). Similar results were obtained with the three-treatment analysis, with the UV-B enhanced cultures generally showing the greatest depression of cell numbers, the UV-B intermediate cultures intermediate, and the UV-B deficient cultures the least growth depression. No significant community shift toward the larger species Thalassiosira weisflogii was noted for the three-treatment study (p>0.050).
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