Plankton is the basic food source in the sea, and all marine life depends upon it. Many different kinds of animals feed directly on plankton, from corals and clams, to crinoids and whale sharks.  

Plankton includes a variety of tiny plants (phytoplankton), animals (zooplankton), and marine bacteria (bacterioplankton). In their early stages of development, as larvae and eggs, many species of mollusks, crabs, fish, and other marine animals form part of the zooplankton. Many zooplankton species feed on other plankton; clam larvae (called veligers) feed on phytoplankton, and jellyfish feed on larval fish. As adults, filter-feeders like bivalves eat all types of plankton using their gills to separate the plankton from the water.

Phytoplankton Bloom

A Phytoplankton Bloom East of New Zealand

Because plankton are so small, they aren’t very strong swimmers. They float in the ocean currents traveling where the wind takes them. Plankton is found in ocean waters all over the world, but is most abundant in coastal areas. In large quantities, plankton can turn water a cloudy grey-green color. These cloudy waters can be seen even in space as they swirl through the ocean.[1]

One interesting type of zooplankton is the arrow worm or chaetognath. This is a predatory marine worm that feeds on other zooplankton. In the Gulf of Mexico, there are 24 species of chaetognaths.[2] This common zooplankter is also an important food source for fish and squid.


Arrow Worm

Phytoplankton is responsible for “half of the oxygen generated by plants on Earth.”[3] Oddly, one type of phytoplankton (called dinoflagellates) contributes to red tide, a phenomenon that turns the water orange-red and makes the water toxic to other marine life, causing them to die and decay which in turn deprives the area of oxygen.[4] Perhaps even more interesting, ancient phytoplankton played an important roll in the development of crude oil deposits. The by-products of photosynthesis helped to create the ingredients that formed the “underlying basis for petroleum or crude oil.”[5] However, the process of creating naturally formed crude oil requires hundreds of years; the fact that crude oil is made of organic matter and waste does not mean that oil is safe for any plankton.

The effects of the oil spill in the Gulf of Mexico on plankton are difficult to determine. However, it is clear that marine life cannot thrive in oily environments. The toxic hydrocarbons and heavy metals found in oil are carcinogenic. As oil disrupts the environment of these small and vital plants and animals, the animals that depend upon plankton for food will be affected in turn. These effects will cascade throughout the food web and marine life of all sizes will be impacted.

[1] What are Phytoplankton?

[2] “Gulf of Mexico: Origin, Waters, and Biota, Volume 1 – Biodiversity, edited by D. L. Felder and D. K. Camp, Texas A&M Press, 2009, pg 1166

[3] Satellite Sees Ocean Plants Increase, Coasts Greening

[4] Phytoplankton Bloom in the Gulf of Mexico : Natural Hazards

[5] Perspectives on Phytoplankton