All Things Plankton

Written by on October 25, 2013 in Marine Life, Other Marine Life

Another HUGE thank you to everyone who already participated in our survey! Many of you have come up with great ideas for topics to cover on MST. Several of those requests have been about plankton, so here’s an overview of one of the organisms that makes all other life in the ocean possible.

As the newly created Plankton Portal (see below) says, “no plankton = no life in the ocean“. Plankton are fundamental to the food web and play an important role in the global carbon cycle.

Diatoms through a microscope.

Diatoms through a microscope. Photo credit: NOAA.

Let’s start with some facts about plankton:

  • Plankton are a diverse group of organisms defined by their inability to swim actively against a current, rather than by biological factors.
  • Plankton comes from the Greek word planktos, meaning “wanderer”.
  • Some organisms are only considered plankton for a certain part of their lifecycle.
  • Plankton vary in size from microscopic diatoms to jellyfish that can be several feet long.
  • Most plankton are less than an inch long.
  • There are two main types of plankton: phytoplankton and zooplankton.

Phytoplankton are marine plants.

  • Some of the most common kinds include diatoms, dinoflagellates, green algae and coccolithophores.
  • Phytoplankton have chlorophyll to capture sunlight and like land plants, they use photosynthesis to turn light into energy.
  • They consume carbon dioxide (making them an important part of the carbon cycle) and release oxygen (making them vital to all life on Earth).
  • When phytoplankton populations grow rapidly in just a few days it is called a phytoplankton bloom. Blooms can occur when there are excess nutrients in the water and can last for weeks. Blooms can be toxic and can result in dead zones
  • Phytoplankton are the foundation of the marine food web. They feed other lots of other marine life, from microscopic organisms to huge whales.

Zooplankton are marine animals that live all or part of their life as plankton.

  • Zooplankton are either very small animals that are too small to swim against a current or large, soft-bodied animals that are weak swimmers.
  • Organisms that are only considered plankton for part of their life are called meroplankton.
  • Jellyfish are gelatinous zooplankton with limited swimming abilities. Tentacles extend from the bell of the jellyfish and they can sort-of swim by pulsing the bell, although they aren’t strong enough to swim against a strong current.
  • Gelatinous zooplankton are characterized by a high water content in body tissues and a delicate structure, both of which make collecting and preserving them incredibly difficult.
  • They are typically translucent.

What is Plankton Portal?

A common Arctic jellyfish, Botrynema ellinorae.

A common Arctic jellyfish, Botrynema ellinorae. Photo credit: Kevin Raskoff, MBARI, NOAA/OER.

Plankton Portal is an online citizen science project where volunteers can help classify millions of underwater images that will help researchers learn more about plankton diversity, distribution and behavior in the open ocean. It was created by researchers at the University of Miami Rosenstiel School of Marine and Atmospheric Science in collaboration with NOAA, the National Science Foundation and

It allows anyone and everyone to explore the open ocean and a vast array of marine life.

Millions of plankton images are taken by the In Situ Ichthyoplankton Imaging System (ISIIS), an underwater robot that has been used in several oceans around the world to detect the presence of larval fish, small crustaceans and jellyfish. The volume of data generated by ISIIS is far too great for researchers alone to classify by hand. Computer programs aren’t a perfect solution either because they can’t classify organisms down to the level that the researchers need. So, the images are now on the web for anyone to help. Don’t worry, there are guides to help you learn how to identify different kinds of plankton. Check it out and let us know if you end up helping out!


Check out our other reader-selected topics:

Copyright © 2013 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .


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