are a vital part of oceanic ecosystems and food webs. They are the primary producers of the ocean, and are grazed on by a range of animals and other organisms. Many plankton are photosynthetic, which means that they produce oxygen[sc:1]. However – as I’m sure most people are aware – they are also the cause of oceanic dead zones which result in mass fish kills and almost irreversible ecosystem damage.
The word plankton comes from the Greek word meaning “wandering”, which is exactly what they do. They are essentially nothing more than free floating organisms which are at the mercy of the ocean’s currents. Although they float with the currents, most of them do have the ability to move vertically within the water column. Many plankton remain microscopic for their entire lives, while others are simply the larvae or immature life stage of larger species[sc:2].
Phytoplankton and photosynthesis
Phytoplankton can be thought of as the plants of the plankton world. Since they photosynthesise, they play a big role in the oxygen cycle. They are abundant in cold, nutrient rich waters where they form the base of the food web, and are an extremely diverse and varied group of organisms. Sub-types of phytoplankton include diatoms, dinoflagellates, coccolithophorids, silicoflagellates, bacteria, and viruses[sc:2].
According to National Geographic, around half of the world’s oxygen is produced by phytoplankton through the process of photosynthesis[sc:3]. That’s right, half of the world’s oxygen production comes from microscopic, plant-like organisms!
To produce oxygen, these phytoplankton need just two things – energy from the sun, which is abundant, and nutrients from the water, which aren’t always as common. It has been argued that we could artificially increase the nutrient concentrations in parts of the ocean to stimulate phytoplankton growth. Certain researchers have argued that increasing iron concentrations could make more phytoplankton grow, which in turn could help remove carbon dioxide from the atmosphere and solve the problem of global warming[sc:3][sc:comma][sc:4]
However, we need to be careful when encouraging plankton growth artificially, as it could lead to fish kills and oceanic dead zones if overdone.
Plankton and dead zones
Sometimes, plankton are responsible for what we know as ‘algae blooms’, and the associated fish kills, oceanic dead zones, and horrible ecological effects. In this case, plankton is actually responsible for a reduction in oceanic oxygen concentrations.
When they die, they sink to the bottom of the ocean, where they decompose. This decomposition process consumes oxygen, which in turns makes the area uninhabitable for most animals. This can cause huge environmental problems including dead zones (like the one in the Gulf of Mexico) and mass fish kills[sc:5].