Ocean Food Web

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For a long time, scientist viewed the marine food web as a way for energy to travel from the plant-like phytoplankton to larger consumers like fish and turtles—big things consuming little things. Now it’s known that the microscopic world has a part to play too.

KEY

Traditional Food Web
Microbial Loop
tuna
Larger Sealife
turtle
Jellyfish
Planktivores
small fish
Ciliates
ciliate
Larger single-celled microorganisms, like ciliates, contribute to dissolved organic matter when they excrete their waste after engulfing a phytoplankton or nanoflagellate in a digestive sack called a food vacuole. Ciliates and other protists are consumed by zooplankton, completing the microbial loop.
Zooplankton
zooplankton
Ocean creatures are often inefficient when it comes to eating. Tiny zooplankton chew through phytoplankton and lose much of what they aim to eat. Instead of being consumed, some of the phytoplankton are ripped apart by munching jaws and the cellular innards are released into the open ocean. Fragments of proteins, lipids, carbohydrates, and DNA become suspended in the water column as dissolved organic matter, during what scientists refer to as “sloppy feeding.”
Nanoflagellate
nanoflagellate
Tiny ocean grazers, like this nanoflagellate, can be voracious predators that help to keep the number of bacteria in the ecosystem in check. Masses of bacteria often consume all the dissolved oxygen within the water, a situation that can cause other marine life to suffocate.
Phytoplankton
phytoplankton
A large source of dissolved organic matter comes from the death of phytoplankton cells due to viruses. Many marine viruses operate through the lytic cycle, a process that causes the host cell to lyse, or burst. Once a virus infects a host phytoplankton cell it replicates itself using the cell’s genetic machinery. The host cell then dies, expelling its inner contents, including the newly grown viruses, into the ocean. Every day, about 20 to 40 percent of marine microbes are infected by viruses.
Dissolved Organic Matter
dissolved organic matter
Invisible to the naked eye, molecular pieces of proteins, lipids, carbohydrates, and nucleic acids (DNA and RNA) drift throughout the water column. Referred to as dissolved organic matter (DOM), these molecules are too small for the average consumer but are perfect sources of fuel for bacteria and archaea.
Microbes
microbes
If not for microbes (bacteria and archaea), the dissolved organic matter found throughout the ocean would be a dead end. By consuming these molecules, bacteria are reintroducing critical energy back into the food web where slightly larger creatures, like nanoflagellates, eat the bacteria, and the cycle continues.