Effect of Exogenous Glucose on Photosynthesis in the Diatom Thalassiosira weissflogii Depending on Nitrate Nitrogen Supply and Illumination

The rate of photosynthetic carbon fixation (P) in the diatom Thalassiosira weissflogii cultivated in the presence of exogenous glucose in the medium (0–10.56 g C/l) at different levels of illumination—25, 50, and 100 E/(m² s)—was studied as a function of nitrate nitrogen supply. In the diatoms limited in nitrogen and assimilating exogenous glucose, P was found to decrease or increase depending on the light intensity, glucose concentration, and the duration of exposure. In the diatoms assimilating both nitrate nitrogen and glucose, compared to those supplied with nitrates alone, P was higher at the medium and high light intensities and lower at the low light intensity. The interrelation of the processes of carbon and nitrogen metabolism in mixotrophic algae and the ecological role of glucose uptake by phytoplankton are discussed.     

Present-Day State of Coral Reefs of Nha Trang Bay (Southern Vietnam) and Possible Reasons for the Disturbance of Habitats of Scleractinian Corals

Our investigations were conducted from 1990 to 2002. Sampling of bottom sediments and biological objects, as well as photo and video shooting, were performed during scuba diving. The state of the environment and coral reef communities was assessed using the chemical–analytical, fluorometric, and luminometric methods, as well as the Ames test and the transect technique. The research results suggest that the spectrum and distribution pattern of persistent congeners of PCDD/Fs (dioxins) in bottom sediments are similar to those of the defoliant Agent Orange and that the bottom sediments are toxic and display photo inhibition and a mutagenic effect. The bottom of the bay is heavily silted throughout its depth. Many large dead colonies of corals without mechanical damage were observed everywhere. The total coverage by live corals in all sites investigated does not exceed 30%. Although, without a doubt, many factors contributed much to the disturbance of the bay ecosystems, the actual trigger for the degradation of the coral reefs seems to be the input of dioxin-containing chemicals used as defoliants during the American–Vietnamese war (Vietnam War).