Morphological variation of the diatom species Gomphonema parvulum Kütz. under nutrient and shading treatment

Diatoms (Bacillariophyta) are unicellular microalgae inhabiting nearly all aquatic environments on Earth. Some taxa are endemic to certain regions, whereas some are widely spread or even cosmopolitan. Diatoms’ species diversity and habitat selection support their use as bioindicators, and traditional water quality indices are based on species composition and index species. However, trait-based indices have gained interest in recent years and researchers believe that traits could potentially act as a useful tool in environmental assessment. Traits refers to the morphological, physiological and phenological properties of species, and they are closely linked to the species’ capacity to grow and reproduce in certain circumstances. Morphological variation in diatoms varies significantly between taxa and species. The possibilities of a diatom to adapt into changing habitat is a result of its capacity to alter its morphological properties. Urban and agricultural land use affect water resources negatively, and climate change acts as a reinforcing factor creating complex and mixed effects on aquatic environments. Global warming is and will proceed to be strongest near the poles and its unique and harsh habitats. Climate change by anthropogenic activities and environmental pollution has affected and will affect microbial communities and primary producers everywhere. Diatoms have a central role in global productivity and biogeochemical cycle, and changes in microbial cell size could have severe implications for food webs and energy transition of energy in the trophic system. The aim of this thesis was to monitor the morphological properties, including the size, shape and striae density, of G. parvulum and its link to different combinations two stressors: nutrient solution (PO4 and NO3) and limited light availability. Shading treatment had a clear effect on average cell width, but average cell length did not correlate with shading. Nutrient treatment did not alter the cell length but had some effect on striae density. However, it was concluded that striae count or head shape are not most suitable for indicator purposes, as they are affected by cell size. In conclusion, no clear variation patterns according to the nutrient or shading treatment were detected, but result suggest that the increased availability of light could alter the size of G. parvulum. Results could be blurred by the small sample size or the presence of cryptic or semi-cryptic species