Phytoplankton are a diverse grouping of around 5,000 species of aquatic microorganisms consisting of eukaryotes, bacteria and archaea, all related in their ability to photosynthesize. Taking the sun’s energy and converting it into food means that these organisms make up the backbone of most aquatic food chains, just like plants do on the land. Deep in the ocean some food chains exist independent of the sun, instead relying on chemicals released from deep sea vents, but that’s a conversation for another day!
The phytoplankton we use to feed our cultures are Tetraselmis and Nannochloropsis, both eukaryotic phytoplankton. Eukarya is a massive grouping made up of any organism that has cells containing a nucleus and membrane bound organelles. Historically, the eukaryotes have been split into: plants, fungi, animals and protists, however recent molecular data has shaken up this classification, separating it into 7 new groups.
Tetraselmis is a green algae, belonging to the archaeplastida, which is made up of the red and green algaes and plants. This genus of algae is found all over the world in both fresh and salt water with most being free-living, although some are symbiotic with animals. Tetraselmis is characterized by its green colour and presence of 4 flagella (whip-like structures which allow a cell to move) and grow to around 10 micrometers long x 14 micrometers wide . Nutritionally and of importance to copepods, rotifers and other phytoplanktivores, tetraselmis has a high lipid (fat) level, making it a good source of energy.
Nannochloropsis is part of the heterokont grouping of eukaryotes, a different lineage of algaes which includes the rather large multicellular kelps which form underwater forests. Nannochloropsis are mostly found in marine environments but can less commonly be found in brackish and fresh water. In contrast to tetraselmis, nannochloropsis is characterised by small spherical cells reaching a size of just 2 to 3 micrometers in diameter, and only has chlorophyll a present in its chloroplasts. Nannochloropsis has high levels of polyunsaturated fatty acids making it a nutritious and energy-rich source of food.
Our phytoplankton blend has a high concentration of both tetraselmis and nannochloropsis. In conjunction they provide a well rounded meal for phytoplankton-eating reef denizens.