Invisible to the naked eye, molecular pieces of proteins, lipids, carbohydrates, and nucleic acids (DNA and RNA) drift throughout the water column. Some are the remnants of a zooplankton excretion, others the cellular innards of a phytoplankton recently attacked by a virus. These molecules are too small for the average consumer but are perfect sources of fuel for bacteria. By consuming the molecules, bacteria are reintroducing critical energy back into the food web when slightly larger creatures, like krill, eat the bacteria. This process is known as the microbial loop.