Feeding the Sea: Phytoplankton Fuel Ocean Life

Phytoplankton fuel ocean life by feeding other plankton, fish, and ultimately bigger creatures. This video explores the diversity of phytoplankton in the oceans and shows why these plant-like organisms play such a crucial role in life on Earth. In some of the images, color-filtering techniques were used to draw out the fine details in the water, but the features are real.


Phytoplankton is among the smallest organisms in the ocean. Yet when they “bloom,” these tiny ocean drifters can cover thousands of square kilometers, which means these primary producers are often visible from space. Known as the “grass of the sea,” they are the first link in the ocean food chain.

As we move around this global map of chlorophyll, we explore the diversity of phytoplankton in the oceans and discover why these plant-like organisms play such a crucial role in life on Earth. Phytoplankton is abundant here when spring melting and runoff freshen the saltwater and add nutrients, just as sunlight increases.

The milky blue waters are probably filled with coccolithophores. Greener areas may be diatoms. Both provide food for marine life. These green blooms likely contain cyanobacteria (blue-green algae). The proliferation of algae in the Baltic Sea has led to occasional oxygen-depleted “dead zones” in the basin. Two major blooms occur here each year. Diatoms peak in May and June, then give way to coccolithophores as certain nutrients run out.

Phytoplankton support Iceland’s productive fisheries. Volcanic ash can fertilize ocean waters with iron, though the North Atlantic usually has enough nutrients to sustain blooms even without the ash. Disko Bay has been essential to the local economy for at least 1,000 years because of its rich marine resources.

Phytoplankton blooms feed the copepods and other plankton and fish that become food for the bay’s shrimp, seals, whales, and walruses. Underwater plateaus off Newfoundland help create circulation patterns that can enrich the waters with nutrients. The waters near the Grand Banks are incredibly productive, supporting catches of swordfish, haddock, lobster, cod, and scallops.

Nutrient-rich water provides fertile conditions for phytoplankton blooms in the Gulf of Alaska. Most nutrients come from upwelling from the depths of river runoff. But dust storms also play a role in supplying iron to the Gulf of Alaska. Fueled by the Oyashio Current, the waters off northeastern Japan support a bounty of phytoplankton and fish.

Abundant blooms of Noctiluca scintillans have been depleting the oxygen and crowding out other species. They are too large to be eaten by copepods; instead, they feed a surge of jellyfish and salps. Storms can stir up the seafloor and bring nutrients to the surface, promoting blooms of phytoplankton. That’s likely what happened here after tropical cyclone Veronica made landfall.

An important player in the ocean nitrogen cycle, Trichodesmium makes seasonal appearances off the northeast coast of Australia. At the Brazil-Malvinas confluence, blooms are stimulated by the ocean’s complex circulation patterns and abundant fronts. The continental shelf off Patagonia is biologically rich due to dust blowing out from the land and nutrients stirred up from the ocean. It is the site of one of the world’s best fisheries. The Benguela current mixes water masses from the Atlantic and Indian oceans as they meet off the capes of South Africa. This dynamic wind and water action cause the ocean to teem with life, from plankton to fish to whales.

Beyond serving as a primary food source for other ocean life, phytoplankton is critical to the global carbon cycle and key oxygen producers that make the planet livable. The remarkable organisms are also quite beautiful.

Ali Kaya


Ali Kaya

This is Ali. Bespectacled and mustachioed father, math blogger, and soccer player. I also do consult for global math and science startups.

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