Maltese microalgae and global climate variability

Abstract

The biodiversity of cyanobacteria and microalgae growing in terrestrial and marine habitats around the Maltese islands is currently being investigated, as limited knowledge exists about the phototrophic microorganisms inhabiting this geographical area. New strains of the genera Oculatella, Albertania, Nodosilinea, Nostoc, Lyngbya, Oscillatoria, Calothrix and Jenufa have been recorded recently. Since the phototrophic microbial biodiversity is currently largely unknown, there is an imminent risk of undescribed microorganisms being lost as a result of changes in microbial community structures due to global climate variability (GCV). We describe a six-month experiment to assess the effects of GCV on two Maltese microorganisms, the filamentous heterocytous cyanobacterial Nostoc strain AD0303 and a coccal microalgal Jenufa strain AD0402. Each strain was cultured under environmental conditions associated with GCV; a temperature (T) of 26 C, enhanced ultraviolet radiation (UVR) and an increased CO2 concentration. Elevated T stimulated growth and biomass accumulation of Nostoc AD0303, whereas growth of Jenufa AD0402 was partially inhibited. Increased UVR had the most prominent effect on cellular morphology. Nostoc AD0303 presented as aggregated filaments, whereas Jenufa AD0402 exhibited thicker cell walls. These UV-protecting mechanisms allowed both strains to accumulate biomass at a significantly higher rate than the control. An increase in CO2 concentration resulted in inhibition of growth in Jenufa AD0402 and bleaching of filaments in Nostoc AD0303, both leading to culture death. A lower CO2 concentration and re-introduction of air subsequently allowed Jenufa AD0402 to grow. So far, this demonstrates that the effects imposed by climate variability are strain-specific, making changes at an ecosystem level difficult to predict.