This unit provides an analysis of seaweed through its definition, classification and taxonomy, scientific nomenclature, seawater and factors of distribution of benthic algae, zoning and relationship with other communities of plankton and benthos, systematic of planktonic microalgae and benthic macroalgae. It also comprises the development of an algal collection, the “red tide” and algoculture and use of macroalgae. It also includes a description of the slides, a glossary and a complementary bibliography.