The bottom of the food web

Plankton are small plants and animals drifting on water currents, and detritus are small particles of decomposing plant and animal remains. These are the source of food for most marine animals. Plant plankton grows by photosynthesis and is eaten by animal plankton; hence, most feeding and living goes on near the surface of marine waters where light penetrates most easily. Plankton populations vary with seasonal conditions, temperature, salinity, and nutrient levels. Riding on the currents with plankton and detritus and feeding are the larvae of molluscs, crustaceans, and bottomfish which in turn are eaten by herring-- which in turn are prey for salmon, sea birds and marine mammals. And so goes the food web.