**6. Plankton economic importance**

In diverse industry areas, microalgae have been widely used as a source for a variety of practices and potential metabolic products, such as food supplements, pharmacological substances, lipids, enzymes, biomass, polymers, toxins, pigments or tertiary sewage treatment. They are also important in aquaculture as a source of nutrients and are of great importance in the production of oxygen, carbon dioxide sequestration and nitrogenous compounds removal, such as ammonia [46, 54, 58]. They are also used as bioindicators, reporting water bodies ecological quality status [47]. However, it is considered that the plankton biotechnology is still young when compared to macroalgal and terrestrial plant biotechnological exploitation and knowledge [79]. Nevertheless, when compared with this two biotechnology branches, it is estimated that plankton have specimens and more suitable, due to their reduced form, being mainly aquatic, a life cycle shortened and rapid adaptation of the metabolism which is capable to produce various interesting compounds [9, 13, 80].

The production of microalgae in different sectors generates social, environmental and economic benefits. For example, in the USA and India, *Haematococcus lacustris* (formerly *Haematococcus pluvialis*) (Chlorophyta) production aims the extraction of astaxanthin, used as a food coloring and also as a powerful antioxidant in the pharmaceutical and cosmetic industry [81].

According to Wijffels [53], marine biotechnology aims to discover new products that can contribute to the health of human beings, such as, for example, new nutraceuticals obtained from algae for use in human and animal feed industries, besides the contribution also in the energy sector, such as the production of biofuels. According to the author, the ω-3 fatty acids, provenly beneficial for human health, can also be a potential source of biofuels. Therefore, the biggest challenge is to obtain these products with quality, in enough quantities and in a sustainable way.
