## 1 Introduction  
Phytoplankton was coined in 1897 using the Greek words \(\varphi\)orov (_phyton_), meaning \"plant\", and \(\pi\lambda\alpha\gamma_{\text{X}\text{TO}_{5}}\) (_planktos_), meaning \"wanderer\" or \"drifter\" [1]. Phytoplankton is therefore a generic term designing unicellular prokaryotic and eukaryotic organisms. Most of the taxa are autotrophic but taxa such as _Polytoma_ sp., _Polytomella_ sp., _Prototheca wickerhamii_, _etc._, have been described with degenerated chloroplasts [2; 3]. These taxa grow heterotrophically in the dark whereas other algae ordinarily grow phototrophically in the light. Despite the fact that the number of newly described species is increasing yearly [4; 5; 6] only a small percentage of species belonging to phytoplankton have been described so far [7]. Phytoplankton has colonized every type of ecological niche, and it constitutes the dominant group of living organisms in term of species diversity in marine waters [8].  
Phytoplankton was playing crucial roles during Earth evolution. For instance, cyanobacteria were at the origin of the rise of the atmospheric oxygen, an event known as the Great Oxidation Event (GOE) [9; 10; 11]. Today, the contribution of phytoplankton to the biosphere continues to be unique because this group largely contributes to the renewal of the atmospheric oxygen and acts as a tremendous sink for CO\({}_{2}\), which is used for the synthesis of organic compounds through photosynthesis [12]. This function makes phytoplankton crucial primary producers on which every food chain relies. While accounting for less than 1% of Earth's biomass, phytoplankton is responsible for more than 50% annual net biomass production [13; 14]. It is known for ages that marine organisms, including phytoplankton, constitute a pretty diversified source of compounds interesting for health, well-being, cosmetics, new fuels _etc._[7; 15; 16; 17; 18]. Actually, it is estimated that approximately 20,000 active substances originating from marine organisms are used in the industry and can be used as an alternative source of chemically synthesized medicine [19]. As mentioned earlier, phytoplankton differentiates from other planktonic taxa by the presence of photosynthetic membranes. In prokaryotic species, the photosynthetic membranes are located within the cytosol whereas in eukaryotic species, they are enclosed in a cell compartment denoted as the chloroplast (for a review, see [20]). Beside the photosynthetic activity, chloroplasts are involved in many biosynthetic pathways and constitute as much as real cellular factories synthesizing crucial cell components such as lipids and pigments [21].  
This manuscript starts with reminders on plastid phyllogeny. Then two families of compounds are considered, _i.e._, pigments and lipids; their diversity is described and their health benefits are detailled. Tetrapyroles and carotenoids have strong anti-oxidant, anti-inflammatory and anti-mutagenetic activities, whereas lipids (essentially polyunsaturated fatty acids) have anti-cholesterol and cardioprotective effects. The following section deals with the cellular increased production of the bioactive molecules by variation of environmental parameters. Because plastids derived from photosynthetic prokaryotes, cyanobacteria have been also considered in this review.