Dear Dr. Universe: How many different types of plankton are there? Are there freshwater plankton? — Arielle, 11

Dear Arielle,

We can find millions and millions of plankton in bodies of water all over the world — from oceans, rivers, and lakes to ponds and mud puddles.

That’s what I found out from my friend Julie Zimmerman, a scientist with the Aquatic Ecology Lab at Washington State University. In the lab, researchers can use powerful microscopes to get an up-close look at these tiny creatures.

There are three main types of plankton, said Zimmerman. One of the groups is phytoplankton. They convert sunlight into energy through a process called photosynthesis, which helps them grow. Phytoplankton are actually quite similar to land plants, but are much smaller, and are the main producers of the oxygen we all breathe.

In fact, scientists estimate phytoplankton produce more oxygen than all the land plants, including the big oxygen producers in the rainforests. They come in lots of shapes and sizes, Zimmerman said. Under a microscope, we can see how some look like the Eiffel tower, a string of pearls, railroad tracks, zig-zags, corkscrews, and stars.

Zimmerman also told me about another group called zooplankton. These animal plankton eat the phytoplankton and other animal plankton. Copepods, a cousin of crabs and the most abundant zooplankton, may be one of the most abundant animals on Earth.

Daphnia are Zimmerman’s favorite plankton. They are related to copepods and are found in freshwater lakes and rivers. They have the amazing ability to grow large, pointy helmets, tail spines, and even neck teeth if they sense predators. She says they are adaptable and also pretty cute.

The third group of plankton are bacterioplankton. These are the recyclers, said Zimmerman. They break down organisms and other animal waste to make nutrients, or food, for some of the plant plankton.

While the plankton within each of these groups have their differences, they also have some similarities. Zimmerman explained that plankton can’t swim against the current like fish do. Instead these organisms drift wherever the current takes them.

“Plant or animal, single celled or multi-celled, big or small, plankton all have one thing in common,” Zimmerman said. “They go with the flow.”

In fact, the world plankton actually comes from the Greek word “planktos,” which means to wander or drift.

When Zimmerman dips her from a research boat into Willapa Bay, she is curious to learn more about the plankton communities. Back at the lab, the team can look at what the plankton eat, how they grow, and see what species might be moving around to new places.

Zimmerman also studies plankton that live in the Columbia River and Vancouver Lake. She reminded me that the amount of plankton we find can change depending on the season or the place. When she goes out to the lake in summer, she can sometimes find a million tiny plankton in just a single teaspoon of water.

Sincerely,

Dr. Universe