Plankton live in both salt and freshwater. Some plankton are bacteria, some are protists (primarily unicellular organisms defined as any eukaryote that is not an animal, plant, or a fungus); but many plankton are actually single-celled plants. They are called “phytoplankton.”

Marine sea algae is a type of phytoplankton. They use photosynthesis to make food, just like large plants. This is a springtime phytoplankton bloom in the Bay of Biscay, off the coast of France. Phytoplankton are the base of the ocean’s food pyramid as well as one of our main sources of oxygen. https://earthobservatory.nasa.gov/images/81102/swirls-in-the-waters-off-france

Scientists estimate that 50% to 80% of the world’s oxygen is produced by phytoplankton.

Zooplankton are the animal type of plankton. They don’t use photosynthesis like phytoplankton. They actually eat plants or other tiny animals.

Krill is one of the most famous types of zooplankton (animal plankton) because baleen whales survive off krill. Krill is at the base of the ocean’s food chain, with an estimated biomass of around 379,000,000 metric tons.

(source)

Many whales, seals, penguins, squid, and fish survive on krill. Krill are also the main prey of baleen whales, including the blue whale (the largest animal that’s ever lived on earth.) This is a rare video of blue whale feeding on krill. Krill are overfished by humans and bans must be enacted to allow their populations to properly thrive.

Plankton and Bioluminescence

Many different kinds of plankton are bioluminescent (they glow at night). Bioluminescence is the production and emission of light by a living organism.

While some algae blooms that glow are ecologically beneficial, some are harmful like the Noctiluca scintillans, seen in the image above.

Harmful algae blooms produce toxins in the water that poison marine life and decimate “good” plankton populations. Human illnesses are caused by harmful algae blooms, and while they’re rare, they can be debilitating or even fatal. Shellfish in harmful algae blooms can be toxic and unsafe to eat. Pollution and climate change are the main factor causing these harmful algae blooms. https://scripps.ucsd.edu/labs/mlatz/bioluminescence/dinoflagellates-and-red-tides/

Many harmful algae blooms appear as red tides in the daytime (not all of them though). Some of these types of algae blooms are caused by the protist kind of plankton, specifically a group of species called dinoflagellates. http://climateandlife.columbia.edu/2017/12/04/studying-bioluminescent-blooms-in-the-arabian-sea/

The term “red tide” is actually being phased out and being replaced with the term “harmful algae bloom” because some harmful algae blooms appear as brown rather than red or, have no color at all.

(photo source)

There is much hope though, humanity IS switching to solar power and electric vehicles (including ships). The earth’s temperature will cool off and stabilize, the oceans will be healthy and clean again, and the plankton will continue to thrive.