Microalgae have long been considered an important food resource, although their quantitative contribution to global food supply is still poorly perceived. The trophic support that phytoplankton provides for fisheries and various aquaculture practices has often been overlooked, with more attention given to controlled production systems using specific microalgae strains. Technological development of mass cultures is progressively generating biomass of some microalgae species that show phylogenetically well-differentiated nutritional profiles. Production costs of phototrophically grown microalgae are slowly declining, although they are still above values compatible with economically feasible use in most feedstuffs. Addition of bulk microalgae in aquafeeds has been the most common practice but optimum inclusion levels are still moderate. Despite showing good levels of essential nutrients such as amino acids and fatty acids, some aspects of biochemical stability, digestibility and bioavailability of specific nutrients need to be better understood in order to achieve higher microalgae ratios in compound diets. Specifically, a more in-depth knowledge is needed about the effects that processing of microalgae biomass exerts on the above aspects. For optimal food use, it must be clear whether it is better to use bulk algae or biomass fractions obtained through purification or biorefinery processes. Microalgae can alternatively be produced from natural populations in managed aquaculture systems where the phytoplankton community structure can be modulated to improve their nutritional value. The aim is to achieve highly efficient food webs for trophic transmission from the base to consumers, represented by aquaculture species that can act both as natural harvesters and as phytoplankton trophic upgraders. Managed phytoplankton production in ponds can be linked to the restoration of degraded coastal ecosystems. It therefore represents an option to contribute to a net increase in the production of marine food resources that are currently exploited to their limit and whose global availability is in a steady state. Both the intensive monospecific production of microalgae other than Dunaliella and the ecosystem approach based on the management of natural phytoplankton communities have been little explored in drylands. Despite the extreme conditions existing in various dryland areas, they offer a good opportunity to increase supply of foods with high nutritional value through production of microalgae. Some key requirements for this will be to have selected strains of microalgae adapted to the environment, to tailor mass production systems to operate in drylands, and to improve knowledge about phytoplankton ecology in such particular conditions.
