View under a microscope showing phytoplankton.

Phytoplankton thrive in the northeastern Pacific Ocean

Phytoplankton are microscopic photosynthetic organisms that float freely in the world’s oceans and freshwater bodies. Also known as microalgae, they play an essential role in aquatic ecosystems, forming the base of the marine food web and generating much of the oxygen on Earth.

The main producers of oxygen in the world

As photosynthetic organisms, phytoplankton release oxygen as a by-product. They are responsible for producing nearly half of the world’s oxygen, making them just as important as terrestrial plants for maintaining breathable air.

Just as terrestrial plants have their own growing and reproductive season, ocean phytoplankton also have their “bloom” seasons. In the Pacific Northeast, these flowers are particularly prominent during the summer months.

Phytoplankton play a role in sequestering carbon

Phytoplankton photosynthesize, converting carbon dioxide into organic carbon. And when they die or are consumed, some of that carbon can sink to the deep layers of the ocean or even to the sea floor, trapping it for long periods. This process makes phytoplankton flourish vital players in the global carbon cycle and potential mitigators of climate change.

View under a microscope showing phytoplankton. Photo: Seth Benson, USGS, public domain.

A vital organism in the marine food chain

Phytoplankton are a vital food source for zooplankton, tiny marine animals that graze these microscopic plants. Phytoplankton also serves as a food source for a wide variety of marine animals including shrimp, snails, and jellyfish. This abundance, in turn, supports larger predators, including fish, marine mammals, and seabirds. In essence, a phytoplankton bloom can boost the entire marine food chain.

Why do phytoplankton thrive?

Phytoplankton blooms are driven by a combination of factors. The most important are light, nutrient availability, water temperature, and physical ocean dynamics.

The northeastern Pacific Ocean is rich in nutrients, especially along the continental shelf and in the upwelling areas. The California Current system is a major coastal upwelling system in the Pacific Ocean and one of the eastern boundary currents in the world.

Benthic turbulence is a process in which cold, nutrient-rich water from the ocean depths rises to the surface, replacing warmer, nutrient-depleted surface waters. This influx of nutrients acts as a fertilizer for the phytoplankton, promoting rapid growth.

Phytoplankton blooms are visible in this satellite image of the ocean waters around Vancouver Island. The swirling green water is a mixture of sediment and phytoplankton. The Pacific Northwest (PNW), a continental shelf, off Vancouver Island is a continental shelf

Satellite image of Vancouver Island showing puffy clouds and green phytoplankton blooms.
Phytoplankton thrives south of Vancouver Island. Satellite image: NOAA-20, July 26, 2023, public domain.

Poisonous flowers

Having a phytoplankton bloom isn’t always benign. Some of them can be harmful algal blooms (HABs), as some species produce toxins that can harm marine life and even pose risks to human health.

Shellfish contaminated with these toxins can cause illness in humans if eaten. In the northeastern Pacific Ocean, one of these harmful algal blooms is the “red tide” caused by some Dinoflagellates.

Satellite image showing phytoplankton blooms off the coasts of Washington and Oregon.
A harmful algal bloom occurred along the coast of Washington and Oregon in July of 2015. This satellite image shows the green swirls of Venus. Image: Landsat 8, July 15, 2015.

In July of 2015, there was a harmful algal bloom along the West Coast of the United States. This bloom included clusters of a type of algae called Pseudo Nicholas. this Algae produce domoic acid, which is a neurotoxin. Since this neurotoxin accumulates in shellfish and seafood, it can cause poisoning in humans.


Karlovich, M.; (2015, August 9). It blooms off the coast of North America. NASA Earth Observatory.

Davis, KA, Banas, NS, Giddings, SN, Siedlecki, SA, MacCready, P., Lessard, EJ, … & Hickey, BM (2014). Estuary uplift of marine nutrients feeds coastal productivity in the United States Pacific Northwest. Journal of Geophysical Research: Oceans, 119(12), 8778-8799.

Perry, MJ, and Epley, RW (1981). Phosphate uptake by phytoplankton in the central North Pacific Ocean. Deep Sea Research Part A. Oceanographic research papers, 28(1), 39-49.


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