Microalgae are small microorganisms with a size of 10 micrometers and have various shapes and colors (Picture 1). Basically, microalgae are aquatic organisms that obtain energy from the sun, like plants that carry out photosynthesis. Therefore, microalgae play a very important role as primary producers in the food web in aquatic ecosystems.

Microalgae are the main food source for marine life, especially young fish, shrimp and crab. Microalgae produce important nutrients such as carbohydrates, proteins, fatty acids and others to support growth. No wonder microalgae species, for example Chlorella are very popular in the market as food supplements for human consumption.

In the aquaculture industry, in addition to being supplied as the main food source for fish and shrimp larvae, microalgae species that produce colorful pigments, such as Haematococcus pluvialis, are also added to the daily diet of ornamental fish, to increase the color brightness on the outside (or derma layer) aquarium fish. When microalgae are cultured in fish farming tanks (co-culture), studies show an increase in the resistance of farmed fish to bacterial or viral attacks (pathogens).

The ability of microalgae to adapt and grow in extreme environments, including the dead sea containing high salt concentrations or seas polluted with heavy metals, allows it to be used in various human activities. For example, microalgae are used for bioremediation processes to treat waters contaminated with heavy metals such as cadmium, copper, lead. Microalgae act by absorbing the metals and producing biomass in large quantities. Furthermore, due to the natural nature of microalgae cells that are capable of accumulating lipids up to 70 percent of their content, microalgae biomass produced in the bioremediation process can also be processed as a raw material for the production of biodiesel fuel.

Although marine microalgae have such a wide range of uses, they also contribute to a number of domestic problems. One of them is the phenomenon of eutrophication. This phenomenon of eutrophication is an uncontrolled explosion of microalgae population that is able to form a barrier layer on the surface of the water and reduce the solubility of oxygen in the water. If prolonged, this phenomenon will cause the death of marine animals on a large scale due to lack of oxygen. Among the causes of nutrient depletion is through the entry of garbage, the disposal of sewage sources and industry irresponsibly through water sources.