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Phytoplankton (Not the SpongeBob Kind)

Oceans and freshwater sources have many similarities and differences, but the core of their food webs remains the same: phytoplankton. Phytoplankton is food for the smallest animal-eating organisms in the water, such as zooplankton, crustaceans, and small fish. These animals are prey for bigger organisms, and the energy is transferred up the food web to organisms such as great white sharks, sea lions, dolphins, and even humans that eat fish. Filter feeders such as basking sharks, flamingos, and whales focus their energy solely on small organisms such as phytoplankton.

Fun fact: the name "phytoplankton" comes from the Greek words phyto, meaning plant, and plankton, meaning to wander or drift. These organisms live on the surface of the water and drift wherever the tides bring them.

Phytoplankton is microscopic plants that, like the trees around us, use sunlight as energy. Because they need light to survive, most live on the surface layer of the seas. These organisms are single-celled and therefore very small- ranging from 2-200 micrometers. As a frame of reference, a standard piece of printer paper has a height of 100 micrometers, and an average piece of human hair is only 70; dust mites average 250 micrometers. Phytoplankton comes in various shapes and sizes, the image below shows the five most common types.

Photo Source: Lindsey and Scott, 2010

As humans, we consume oxygen and release carbon dioxide. Phytoplankton does the opposite, consuming carbon dioxide and providing the earth with about half of all of its oxygen (the rest comes from trees and macroalgae such as seaweed). In addition to being the base of food webs and providing oxygen, phytoplankton can also be used as an indicator of ocean health. Blooms occur when phytoplankton abundance increases so rapidly that the color and texture of surface water in an area change. You may be thinking, “hey, more phytoplankton should be a good thing”. Sadly, as with all aspects of life, a careful balance must occur. When the organisms reproduce at such rapid rates, they exhaust nutrients and can die just as fast as they were born. This causes them to sink and decompose, depleting the surrounding water of vital nutrients which often leads to a “dead zone”. An area without nutrients will not allow any marine life in the area to survive. Changes in water temperature, salinity, and density are factors that can lead to these blooms.

When under normal conditions, phytoplankton truly provide the base of all life- not just in the ocean, but for the whole planet. Warming waters are making it difficult for them to reproduce at the necessary rates and strongly influence their growth rates. Studies are showing decreases in phytoplankton worldwide, with the biggest threat being climate change. Charismatic species such as whales and polar bears are often the first consideration when we hear about climate change (remember those sad commercials with the ice melting?), and while they are at risk, if we lose our phytoplankton, everyone is at risk. Forgive me if I sound dramatic, but these tiny plant-like organisms the same width as my hair truly control our world.


Lindsey, R., Scott, M., & Simmon, R. (2010). What are phytoplankton. NASA’s Earth Observatory.

Silva E, Counillon F, Brajard J, Korosov A, Pettersson LH, Samuelsen A and Keenlyside N (2021) Twenty-One Years of Phytoplankton Bloom Phenology in the Barents, Norwegian, and North Seas. Front. Mar. Sci. 8:746327.

Shukla K.K. (2022). Importance of Phytoplankton and their impact to the Global Ecosystem: An Overview. Int. J. of Pharm. & Life Sci., 13(3): 22-25.


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