Plankton: We should be thanking these microscopic critters!

Plankton: We should be thanking these microscopic critters!

The below article was written by Priya Thamburaj as part of her senior mentorship project with Save Coastal Wildlife nonprofit. Priya graduated in June 2021 from the Biotechnology High School located Freehold, Monmouth County, NJ. She spent several weeks studying plankton populations in Sandy Hook Bay & Raritan Bay, NJ.

If you heard the phrase “lungs of the planet,” the first thing you might think of is the great Amazon rainforest which covers a large chunk of South America. The Amazon is indeed significant in its role as a carbon sink, meaning that plants in the Amazon, just as in any other rainforest, sequester carbon from the atmosphere through photosynthesis. Sequestering carbon to the ground is important because rising levels of carbon dioxide in the atmosphere is the major cause of global warming. Deforestation could contribute to up to 20% of greenhouse gas emissions caused by humans.

But you might be surprised to hear that the Amazon rainforest only produces 6% of the oxygen made by photosynthetic organisms on the planet, and rainforests as a whole make up about one third of that oxygen. Where in the world does the rest of our oxygen come from? Why, the ocean of course! People stress the importance of trees so much that sometimes we forget that 70% of our planet is covered by oceans, which have plenty of photosynthesizing organisms!

A few days ago, I went to Bayshore Waterfront Park in Port Monmouth at 10 pm to collect a few water samples. I walked to the edge of the pier and dragged my collecting device (a little container at the end of a net funnel) through the water a few times. When I went to look at my water samples under a light microscope, I was amazed at what I saw! The view was sprinkled with star-like shapes enclosed in circles, and there were endless dots organized into neat rows. These structures are different types of diatoms, which make up 75% of all phytoplankton. 

Diatoms under a light microscope, seen at 40X magnification

Phytoplankton are the members of the plankton community that are classified as primary producers, meaning that they make their own food through photosynthesis. Phytoplankton make at least half of all oxygen that is produced by all photosynthesizing organisms on Earth, which is significantly more than land plants. They can be found near the surface of any body of water, using sunlight to take up carbon dioxide to make food, releasing oxygen as a byproduct. The ocean actually absorbs about one quarter of the carbon dioxide produced from greenhouse gas emissions. Not only do phytoplankton take up carbon dioxide from the atmosphere, but they also make up the backbone of aquatic food webs. A wide variety of aquatic animals-- from microscopic zooplankton (animal plankton) to fish and whales-- depend on phytoplankton for food. 

Marine organisms are classified as plankton if they drift along with ocean currents without having the ability to move against currents on their own. Among the organisms I observed under the microscope were tiny little crustaceans called copepods, which are classified as zooplankton. Copepods are one of the most abundant types of zooplankton and are an extremely important food source for small fish and other crustaceans such as krill. Under the microscope, copepods really do look like the plankton character from Spongebob!

Copepod under a light microscope, seen at 40X magnification

During the day, zooplankton stay in deeper areas of the ocean to avoid being eaten by predators. Then, during the night, they migrate to the ocean surface to feed on phytoplankton. That’s why I collected my samples at night when the copepods would be feeding at the ocean surface, and sure enough, my sample was teeming with them!

Even though we can’t always see them with the naked eye, plankton are incredibly important for all life on the planet, including us! They’re an essential carbon sink that acts against global warming and make up the base of aquatic ecosystems. It’s unclear how exactly climate change will impact plankton populations. Warm waters might actually increase plankton populations, but when plankton exhaust the amount of nutrients available to them, it could result in a net decrease of plankton. Other sorts of human activity also affect plankton populations. For example, zooplankton may accidentally ingest plastics in the water, and nutrient runoff causes algal blooms that throw off ecosystems. 

The role of rainforests in climate change is definitely important, but plankton deserve more credit and attention! So, next time you go to the beach, make sure to thank your microscopic plankton friends and take your trash home!

A female copepod with eggs.