Phytoplankton of the Northwest U.S. Shelf Ecosystem

Microscopic algae known as phytoplankton are the base of most marine food webs. Phytoplankton contain chlorophyll which is used to capture sunlight and convert carbon dioxide and water into oxygen and carbohydrates.

West Coast

What Are Phytoplankton?

Almost all life on Earth relies on photosynthetic organisms such as plants and algae for oxygen production. In the Northwest U.S. continental shelf ecosystem, microscopic single-celled algae known as phytoplankton are responsible for nearly all primary production. Globally, primary producers generate almost half of Earth’s oxygen and are the base of most marine food webs. They are also important components of carbon cycling and sequestration—the process of capturing and storing atmospheric carbon dioxide. Ultimately, how many organisms that can live and grow in a given area depend on the amount of primary production generated by the phytoplankton.

Alexandrium (left) is a toxic dinoflagellate species. Pseudo-nitzschia (right) is the marine algae species that produces the toxin domoic acid.

There are more than 20,000 species of phytoplankton distributed among eighth major taxonomic groups. They range in size from less than 1 µm to greater than 100 µm. The distinct phytoplankton groups have different primary functions in the ecosystem. They also have different effects on food availability, biogeochemical cycling, and carbon export to the deep ocean. The Northwest Fisheries Science Center actively cultures several species of phytoplankton. These cultures serve as a resource for research and a part of outreach activities with the commercial aquaculture community and Universities.

What Is Primary Production?

Photosynthesis involves the capture of light energy by plant pigments such as chlorophyll. This energy converts water and carbon dioxide into carbohydrates (sugars) and oxygen. Primary productivity is simply the rate of photosynthesis and uptake of dissolved nutrients such as nitrate and phosphate to produce more plant matter or biomass. High primary productivity regions are often “hot spots” for fish, turtles, birds, marine mammals, and benthic shellfish in shallower areas.

Phytoplankton and Shellfish

Phytoplankton blooms are a major component of the food web and a primary food source for zooplankton and filter feeders such as shellfish. Coastal razor clamming brings thousands of dollars to Pacific Northwest coastal economies during seasonal digs for tourists and tribal subsistence harvesters. Washington State is a national leader in farmed bivalve shellfish, an industry that employs more than 3,200 people in family-wage jobs and contributes an estimated $270 million to the economy.

Razor clamming on the Washington coast.

At the Northwest Fisheries Science Center, we have established early warning systems for phytoplankton that can lead to shellfish closures and kills, marine mammal mortalities, and human illness. These “alert” systems provide real-time information to the state, tribes, and shellfish growers to prevent or minimize mortalities and optimize harvest potential.

These early warning systems include SoundToxins, Olympic Region HAB partnership, and the Pacific Northwest HAB Forecasting Bulletin.

Where Are Phytoplankton?

Several environmental and oceanographic factors influence the abundance, composition, spatial distribution, and productivity of phytoplankton. The principal elements are:

Amount of sunlight.
Availability of major nutrients.
Water temperature.
Physical oceanographic processes such as vertical mixing, upwelling, currents, and tides.
Grazers such as zooplankton and shellfish.

When the growing conditions are ideal for a specific species, the phytoplankton population can grow exponentially and create a “bloom.”

700X385 Satellite image harmful algal bloom forecasting NWFSC.jpg

NOAA scientists monitor satellite images like this for high chlorophyll that may be algal blooms.

The unique physical characteristics of the Northwest U.S. continental shelf help make it among the most productive continental shelf systems in the world. However, there are large seasonal and regional differences in phytoplankton. The most apparent spatial pattern, which we can observe using satellite remote sensing data, is the decrease in phytoplankton abundance from the coast to the shelf break.

Harmful Phytoplankton

Pseudo-nitzschia is a marine alga that produces a toxin called domoic acid. An excess abundance of Pseudo-nitzschia can result in a harmful algal bloom that can shut down shellfish fisheries, cause marine mammal mortalities, and impact human economic and social well-being.

Harmful algal blooms (HABs) can produce toxins harmful to humans, fish, shellfish, marine mammals, and birds. We also call HABs a “red tide,” as some harmful species contain red pigments that turn the water red at high populations. Other blooms can be brown, yellow, or green, but the color does not necessarily indicate that a bloom will be harmful to marine animals or humans.

There are several HAB species in the Northwest. One of the most well-known HABs is the toxic dinoflagellate Alexandrium catenella, which produces saxitoxins accumulating in shellfish. This species can cause paralytic shellfish poisoning in humans and other consumers. Other common HABs problematic in the Pacific Northwest are the dinoflagellate, Dinophysis, which cause diarrhetic shellfish poisoning, the diatom, Pseudo-nitzschia, that causes amnesic shellfish poisoning, and Heterosigma, that causes fish kills.