If mortality is greater, then the population decreases. These favorable conditions depend on high concentration of nutrient rich water, rapid cycling of materials by decomposers, high numbers or rapid turnover of producer organisms Light nutrients including nitrate, phosphate, silicon, potassium, magnesium, copper, iron. Silicon dioxide needed for outer glass covering of diatoms and forms internal structural parts of sponges, K and NO4 and PO4 needed in plant proteins, lipids and carbohydrates during photosynthesis. Plankton comprise the large and small organisms that drift or float while tides and currents move them through the water. Most plankton do have a limited ability to move and can migrate vertically through the water from day to night.
Plankton is very important as it occupies the first two or three links in the marine food chains.
Nekton use fins, jets of water, strong flippers, flukes and flippers to swim through the water. If the organism resides primarily in or on the substrate and doesn't swim or drift for extended periods as an adult it is considered benthic. Demersal organisms, such as flounder alternate between swimming and resting on the bottom. Living on the bottom are epifauna and living within are infauna. The substrate could be a source of food.