Microbial Loop

Winner of the Discover the Microverse 1 minute video competition at ISME18!

The marine food web is messy.  In each drop of seawater, there are thousands of microscopic algae growing in the sunlit surface ocean and providing the primary energy source for marine life.  Algae transform inorganic carbon dioxide (CO2) into an organic food source for tiny, yet very hungry planktonic grazers. Gradually, this energy is transferred to larger predators, until it reaches the fish sitting at the top of the food web.

Ooze… Munch munch… Squirt… This is an inefficient process. As algae grow, they leak organic carbon back into the surrounding water. Grazers are sloppy as they eat, shredding algae and wasting precious organic carbon as well. Larger organisms also excrete material contributing to this pool of dissolved organic carbon, creating a major loss for the movement of energy through the food web.

However, there are organisms even smaller than algae that love to consume these dissolved organics. Bacteria feast on these molecules providing a ‘microbial loop’ for the organics to re-enter the food web. While bacteria respire much of this carbon back into CO2, the rest is again available to move up the food web. These microbes ultimately process about half of the organic carbon produced in the ocean.