## 6 Conclusion and Perspectives  
Phytoplankton is an exceptionnal source for a variety of bioactive compounds. Among them, pigments and lipids are recognized to have numerous positive effects on health. Very often, synergistic actions between these two kinds of molecules are described. Actually, most studies are done _in vitro_, so it is necessary to develop clinical tests to evaluate their ability, _in vivo_, to avoid some human diseases as well as their possible secondary effects. More, additional intervention trials are required with pigments to precisely determine their absorption, metabolism and potential as natural anti-oxidant, anti-inflammatory and anti-mutagenic compounds _in vivo_. However, phytoplankton remains largely unexplored and, until now, very few commercial achievements of microalgal biotechnology have emerged [288]. Also, increased harvesting of commercial algae can be considered beneficial for the environment, as they are photosynthetic, _i.e._, carbon dioxide-absorbing organisms, and thus their cultivation can limit greenhouse gas emissions [289]. [PERSON] _et al._[290] engineered strategies for simultaneous enhancement of phycocyanin production and CO\({}_{2}\) fixation with _Spirulina platensis_. Microalgae are usually cultivated under light. Light is required to get more Chl [291]. However, some species (e.g., _Chlorella protothecoides_, _Crypthecodimium cohnii_, _Schizochytrium limacinum_, _Haematococcus pluvialis_) can be grown heterotrophically [292]. They are cultivated in the dark thanks to a carbon source replacing the more expensive traditional support of light energy. This kind of culture is generally restricted to small volumes of high-value products. Other microorganisms (e.g., _Haematococcus pluvialis_, _Scenedesmus acutus_, _Chlorella vulgaris_, _Nannochloropsis_ sp.) also have the ability to grow mixotrophically (with a mix of different sources of carbon and energy). Via this technique, BioReal (Sweden) was the first company to produce and commercialize Asta (15 to 30 T/year) [293]. In this review, we have showed that different parameters can be used to increase pigment and lipid production, e.g., temperature, nutrient starvation, nitrogen concentration, desiccation, CO\({}_{2}\) level, salt stress or metal stress. Whatever their means of production, some species are cultivated in large volumes and given as food supplement for their global health benefits. This is the case for _Tetraselmis suecica_, _Botryococcus braunii_, _Neochloris oleoabundans_, _Isochrysis_ sp., _Chlorella vulgaris_, _Phaeodactylum tricornutum_ and _Odontella aurita_[110,120]. When particular growth conditions are applied on a microalga species with the goal to optimize the production of one interesting molecule, it is not rare that another interesting molecule is also produced. For instance, [PERSON] _et al._[294] succeeded in cultivating a _Scenedesmus almeriensis_ strain rich in oils and carotenoids, and in lutein in particular. Nowadays, production of carotenoids has become one of the most successful activities in algal biotechnology, because of the demand for natural products, instead of being chemically synthesized, despite the fact that synthetic carotenoids have a lower production cost [293]. Carotenoids and especially \(\beta\)-carotene as pigments, are utilised in food and beverages, but also in aquaculture feed [143,148]. Some mg of \(\beta\)-carotene per gramme biomass can now be obtained from microalgae(_Isochrysis_, _Phaeodactylum_, _Chlorella_ sp. and _Tetraselmis suecica_) or cyanobacteria (_Spirulina_) mass cultures [110,151]. The estimated market size for natural \(\beta\)-carotene is 10-100 tonnes year\({}^{-1}\) and its price is \(>\)750 \(\epsilon\) kg\({}^{-1}\)[151,295]. Increasing the production of Asta is also an advantageous goal.