"As we continue to study the intricate associations that characterize the coral holobiont, we are coming to realize the extent to which it depends upon bacteria. This should not be so surprising. Bacteria are the predominate plankton on a tropical coral reef. They accordingly make up a considerable amount, if not the bulk, of the typical coral planktivore’s diet."
When PNSB are floating around in the water column, if ammonia and/or nitrate is present in appreciable amounts, the bacteria will remove theses wastes!