The tutorial addresses the most important issues in marine botany. The main attention is paid to the biological and environmental features of the life of micro- and macroalgae in the conditions of the northern seas. The manual is intended for a wide range of students: bachelors, masters and graduate students studying in the areas of training "Biology," "Ecology and nature management," "Aquatic biological resources and aquaculture," as well as for teachers participating in the workshop on marine biology.