What is Marine Phytoplankton?


Plankton are some of the most amazing plants in our world. The name comes from the Greek which means ‘wanderer’ and it’s an apt term to describe this diverse and fascinating collection of waterborne organisms that are unable to swim against the current but drift through our world’s oceans, sustaining much of the life on our planet in the process.

Amongst these wanderers, a special group are known as autotrophic, which means they have the ability to produce complex organic compounds from substances in their surroundings, including carbon dioxide. Phytoplankton (from the Greek ‘phyto’ meaning plant’) are the most commonly known of these extraordinary marine organisms that inhabit the upper layer of our oceans, where they are touched by the light of the sun.

Phytoplankton and Primary Production

It may be said that every species on our planet relies either directly or indirectly upon the process of primary production. This is the process whereby organisms such as phytoplankton use sunlight to synthesize complex organic molecules from simpler inorganic compounds in a process known as photosynthesis. Effectively, they are converting light energy into chemical bonds stored within plant tissue. For those of us species who lack the capability of fixing light energy, this is an extraordinary gift.

Ecology of Planktons

As well as relying upon the availability of sunlight, certain other things are crucial to the wellbeing of phytoplankton. Macronutrients such as nitrate, phosphate and silicic acid aid their survival, as does the presence of iron, Vitamin B, and of course carbon dioxide. They are highly sensitive to water temperature, salinity, their distance from the surface, and even prevailing wind direction. When conditions are right, however, their growth can increase at phenomenal levels. Known as a phytoplankton ‘bloom’, these may be large enough to be visible in satellite images, and cover hundreds of square miles of ocean. Blooms may in themselves last up to a few weeks, though the individual plankton themselves live a few days at most.

Planktons as Producers of the World’s Oxygen

Most scientists gauge the oxygen producing capabilities of plankton to be significantly more important than those of the world’s forests, producing up to 70% of our planet’s oxygen. Equally, their role in controlling CO2 balance is of inestimable importance and, if current estimates of their decline are correct, any depletion in phytoplankton concentrations in our oceans could have devastating effects on our environment. Phytoplankton are at the very base of what scientists term ‘oceanic biological productivity.’

Foundational elements in our food web

The importance of these humble plants is really too great to accurately describe. Situated right at the bottom of the food chain, these microscopic life forms feed tiny zooplankton, armies of krill, and even some our planets largest species such as whales.