Microorganisms modify their biochemical composition in response to environmental factors, including nutrient availability, light, temperature and salinity. This research was carried out in order to establish ways of modifying the biochemical composition of marine cyanobacteria through the optimization of environmental parameters e.g. light, temperature and salinity. The effect of salinity stress in combination with variable temperature and light intensity was studied on Synechocystis sp., strain Ol 86, isolated from the North Sea. In nature, all microorganisms are exposed to different factors. Hence, we considered all the essential factors together in different groupings. Experiments were conducted at three different temperatures, two different light intensities and four different salinities. The influence of these factors on the growth and physiology of cyanobacteria from a microbial mat of the North Sea is reported.