Phytoplanktons are the microscopic plant wanderers found in the different layers of ocean. These microorganisms are the basis of food chain in aquatic life. Being autotrophic in nature, they depend upon sunlight and carbon dioxide for their livelihood. They account for half of the photosynthetic activity on earth, hence responsible for much of the oxygen present in the Earth's atmosphere. Ocean has a tremendous treasure of minerals which help in the growth and development of phytoplankton. Now the question arises that why I am talking about these inhabitants of ocean? How and in what way they are useful to us? The answer lies within their characteristics. They utilizes carbon dioxide for their food, thus removing carbon dioxide from our atmosphere. They also produces Dimethyl Sulphide (DMS) which help in regulating climate.

We already know that our technological development, advancement in different sectors, modernization has a dangerous and an envious impact on our nature. The coming generation is definitely going to pay a lot for our deeds. We all are aware about the potential effects of global warming which are accelerating at a high rate. This has forced the researchers, scientists, scholars of different nations to work in this direction and find means to minimize the atmospheric greenhouse gases which are the main cause of global warming. One of the most worrisome greenhouse gases comes from quite natural sources. In fact, all of us breathe out about two pounds of it daily. This gas is, of course, carbon dioxide. A number of ingenious and significant ideas have been proposed to reduce the amount of carbon dioxide in the atmosphere. Some of these plans include reducing the production of greenhouse gases from automobiles and industrial emissions, and maximizing trees (including in urban areas) to act as a carbon sink. One of the more fantastic possibilities given scientific attention has been sequestering carbon dioxide in the oceans and this can be easily done by phytoplanktons.

Many scientists are working with phytoplanktons and trying to enhance their production in every possible manner. If we emphasise on their requirements and adequate growing conditions, we find that they have got few necessities like sufficient amount of carbon dioxide, sunlight in a process called photosynthesis to produce organic compounds which they use for food and to make their cells. An adequate amount of temperature and pressure are necessary for their growth. So they are generally found in the euphotic region of the ocean. Phytoplankton can become limited by the availability of nutrients when light and temperature are adequate and loss rates are not excessive. The current paradigms for nutrient limitations in freshwater, estuarine, and marine environments are quite different. The internal cellular concentrations of nutrients determine phytoplankton growth rates, and it is often difficult to relate growth rates to external concentrations, especially in natural situations. This should lead to a greater reliance on the composition of particulate matter and biomass-based physiological rates to infer nutrient limitation. The phytoplankton require phosphorus (phosphate), nitrogen (nitrate, nitrite, ammonia) and silicon in large amount for their growth and development. They also require very small amounts of metals such as iron, copper, zinc and cobalt.With these limited requirements, they sequester carbon dioxide from air into deeper parts of ocean. At the same time, they produces oxygen and DMS helping in sulphur cycle. This coupled effect leads to anti global warming and cooling effect in atmosphere.

Phytoplankton produces DMSP (dimethylsulfoniopropionate) which cleaves into DMS which regulates our environment. DMSP acts as osmolyte and cryoprotectant which saves the life of phytoplankton species from saline water bodies, freezing temperature and high pressure. Phytoplankton species are generally obligate photoautotrophs, mixotrophs and heterotrophs. Of these, the best known are dinoflagellate genera such as Noctiluca and Dinophysis, that obtain organic carbon by ingesting other organisms or detrital material and diatoms such as are coscinodiscus wailesii , closterium, coscinodiscus radiates, thalassiosira pseudonana, thalassiosira levanderi, orthoseira roeseana . In some areas such as the Sargasso Sea or the South Pacific Gyre, phytoplankton is dominated by the small sized cells, called picoplankton, mostly composed of cyanobacteria (Prochlorococcus, Synechococcus) and picoeucaryotes such as Micromonas. In both aquaculture and mariculture phytoplanktons are utilised as food for the animals being farmed. In mariculture, the phytoplankton is naturally occurring and is introduced into enclosures with the normal circulation of seawater. In aquaculture, phytoplankton must be obtained and introduced directly to feed many varieties of aqua-cultured molluscs, including pearl oysters and giant clams.

The phytoplankton are cultured artificially under some specified conditions for a variety of purposes such as food stock for other aqua cultured organisms, a nutritional supplement for aquatic life. Culture size range from small-scale laboratory cultures of less than 1 liter to several tens of thousands of liters for commercial aquaculture. Regardless of the size of the culture, certain conditions must be provided for efficient growth of phytoplankton. The sterilized seawater of a specific gravity of 1.010 to 1.026 is used as a culture medium. Various fertilizers are added to the culture medium to facilitate the growth of plankton. A culture must be aerated or agitated in some way to keep plankton suspended, as well as to provide dissolved carbon dioxide for photosynthesis. In addition to constant aeration, most cultures are manually mixed or stirred on a regular basis. Light must be provided for the growth of phytoplankton. The appropriate temperature of 6500 K and the light duration of 16 hours per day is the most efficient growth conditions for phytoplankton.

Researchers are trying their level best to increase the production of phytoplankons in our Eco system specially in those regions of ocean (High Nutrient Low Chlorophyll) where the population of phytoplanktons are merge. This can be improved by iron fertilization because iron is an essential micro-nutrient for the growth of phytoplankton. Lack of iron limits the growth of phytoplankton, thus reducing the biological removal and storage of carbon in deep ocean. This study help us to realize that ocean and its life plays a big role in minimizing the effects of global warming. We should move together with these ocean dwellers in the mission of saving our mother Earth. This is the only way left for us to gift a beautiful nature to our successors.

About Author / Additional Info:
Geetanjali Murari
B.Tech (Biotechnolgy)
Hazaribag, Jharkhand