Phytoplankton




Phytoplankton are the autotrophic component of the plankton that drift in the water column. The name comes from the Greek terms, phyton or "plant" and ???????? ("planktos"), meaning "wanderer" or "drifter"[1]. Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, they may appear as a green discoloration of the water due to the presence of chlorophyll within their cells (although the actual color may vary with the species of phytoplankton present).

Phytoplankton, like plants, obtain energy through a process called photosynthesis, and so must live in the well-lit surface layer (termed the euphotic zone) of an ocean, sea, or lake. Through photosynthesis, phytoplankton (and terrestrial plants) are responsible for much of the oxygen present in the Earth's atmosphere. Their cumulative energy fixation in carbon compounds (primary production) is the basis for the vast majority of oceanic and some freshwater food chains (chemosynthesis is a notable exception). As a side note, one of the more remarkable food-chains in the ocean — remarkable because of the small number of links — is that of phytoplankton fed on by krill (a type of shrimp) fed on by baleen whales.

Aside from light, phytoplankton are also crucially dependent on the availability of nutrients for growth. These are primarily macronutrients such as nitrate, phosphate or silicic acid, whose availability is governed by the balance between the so-called biological pump and upwelling of deep, nutrient-rich waters. However, across large regions of the World Ocean such as the Southern Ocean, phytoplankton are also limited by the availability of the micronutrient iron. This has led to some scientists advocating iron fertilization as a means to counteract the accumulation of anthropogenic carbon dioxide (CO2) in the atmosphere.

While almost all phytoplankton species are obligate photoautotrophs, there are some that are mixotrophic and other, non-pigmented species that are actually heterotrophic (the latter are often viewed as zooplankton). Of these, the best known are dinoflagellate genera such as Noctiluca and Dinophysis, that obtain organic carbon by ingesting other organisms or detrital material.

Unless your reef tank/fish tank is completely sterile, then there will be microscopic life in your system,not just bacteria in the filters but also phytoplankton & zoo-plankton.Adding phytoplankton kick starts a massive chain reaction that helps your system turn into its own echo-system. Phytoplankton is a vital source of nutrients for your reef inhabitants. Apart from the requirement for micro-algae for culturing and/or enriching live prey organisms such as Artemia and rotifers algae are often used directly in the tanks for rearing marine fish larvae. This “green water technique” The effects of the presence of micro-algae in the larval rearing tank are still not fully understood and include: · stabilizing the water quality in static rearing systems a direct food source through active uptake by the larvae with the polysaccharides present in the algal cell walls possibly stimulating the non-specific immune system in the larvae; · an indirect source of nutrients for fish larvae through the live feed (i.e. by maintaining the nutritional value of the live prey organisms in the tank); · increasing feeding incidence by enhancing visual contrast and light dispersion, and · microbial control by algal exudate's in tank water and/or larval gut.

Phytoplankton are a key food item in both aquaculture and mariculture. Both utilize phytoplankton 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. The plankton can either be collected from a body of water or cultured, though the former method is seldom used. Phytoplankton is used as a foodstock for the production of rotifers,^[10] which are in turn used to feed other organisms. Phytoplankton is also used to feed many varieties of aquacultured molluscs, including pearl oysters and giant clams.

The production of phytoplankton under artificial conditions is itself a form of aquaculture. Phytoplankton is cultured for a variety of purposes, including foodstock for other aquacultured organisms,^[10] a nutritional supplement for captive invertebrates in aquaria. Culture sizes range from small-scale laboratory cultures of less than 1L to several tens of thousands of liters for commercial aquaculture.^[10] Regardless of the size of the culture, certain conditions must be provided for efficient growth of plankton. The majority of cultured plankton is marine, and seawater of a specific gravity of 1.010 to 1.026 may be used as a culture medium. This water must be sterilized, usually by either high temperatures in an autoclave or by exposure to ultraviolet radiation, to prevent biological contamination of the culture. 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 colour temperature of illumination should be approximately 6,500 K, but values from 4,000 K to upwards of 20,000 K have been used successfully. The duration of light exposure should be approximately 16 hours daily; this is the most efficient artificial day length.^[10]