The ocean is home to a vast number of living things. Just as on land, these organisms depend on each other for food. Phytoplankton are microscopic single-celled plants that drift through the water column. Here is what phytoplankton look like under a microscope.
Phytoplankton cells have a lot of surface area in relationship to their volume. This helps phytoplankton remain suspended near the surface where they can receive sunlight.
Phytoplankton are primary producers as well as the base of the food chain. They can convert the sun’s energy into food through the process of photosynthesis. Photosynthesis is the process in plants that transforms radiant energy from sunlight to chemical energy that they can use to grow. Plants make organic substances and release oxygen from carbon dioxide and water when energy from the sun is absorbed in their chlorophyll pigments.
The basic reaction is:
carbon dioxide + water + light energy = glucose + oxygen + water
Here is a simplified diagram:
Phytoplankton also gather energy from nutrients normally found in the sediment on the seafloor. When there is plenty of sunlight and nutrients, phytoplankton multiply rapidly. At certain times, in certain circumstances, a much greater quantity of nutrients than normal reaches the phytoplankton. Usually, this takes place during an upwelling event, when cold, nutrient-rich water flows up to the surface. This results in masses of phytoplankton being produced during a short time. This is called a bloom.
Plankton are the base of the food web. Zooplankton are microscopic animals that live in the ocean. They are the primary consumers that eat the phytoplankton. Small fish, the secondary consumers, eat the zooplankton, which are then eaten by larger organisms (tertiary consumers). A food chain is a simple way to show the relationship that exists among the various plant and animals.
Here is an example of a marine food chain
Most animals eat of variety of food just as you do. A food web is a diagram that shows how organisms in several different food chains are interconnected.
Click here to go to a NASA website for more information