What is Mixotrophy?

This is Jim Fiorendino, your host for On the Ocean

What if you were hungry, and could have lunch by taking a walk in the sun, and later, for dinner, enjoy a hamburger? There are organisms in the ocean, called mixotrophs, that can do exactly that!

In the past, organisms have been described as autotrophs or heterotrophs based on how they meet their nutritional needs. A heterotroph needs to eat to survive, while an autotroph can make its own food, and does not need to eat. Humans are heterotrophs, while organisms like plants are autotrophs.

Phytoplankton are important autotrophs present in all the world’s oceans. These microscopic organisms rely on photosynthesis to produce the food they need to survive. During photosynthesis carbon dioxide, water, and light energy from the sun are converted to food for phytoplankton. Several marine phytoplankton, previously thought to be strictly autotrophs, have been found to utilize both autotrophy and heterotrophy. These organisms, known as mixotrophs, can obtain the food they need from both photosynthesis and predation on other marine organisms.

In a typical marine food chain, phytoplankton form the base, photosynthesizing and creating food for themselves. Heterotrophs like zooplankton graze on phytoplankton. Zooplankton are, in turn, eaten by higher predators like fish. Recently, scientists have realized that treating marine ecosystems as a chain of predators and prey is inaccurate, particularly when attempting to describe the interactions of microscopic organisms.

Instead of a simple, tiered food chain, with autotrophs at the bottom and major predators at the top, a more accurate depiction of marine predator and prey relationships would look like a web. Restructuring the marine food web to account for mixotrophy has many important implications for ocean ecosystems that scientists are now trying to understand.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script author: James M. Fiorendino