Plankton
The most abundant life forms in the ocean are plankton; most are so small that you
can’t even see them (Figure14.28). These include many types of algae, copepods, and
jellyfish. Because exploring the oceans is much harder than studying the land, many marine
organisms haven’t been extensively studied by humans. Scientists believe many species of
marineorganismshaven’tevenbeendiscoveredyet. Theplanktonareonegroupoforganisms
that have been studied extensively. The word ”plankton,” which comes from the Greek for
wanderer, describes how these organisms live. All plankton float freely or drift, wandering
at the ocean’s surface.
The first link in all marine food chains are thephytoplankton, or ’plant’ plankton, which
use sunlight to make sugars from carbon dioxide and water (photosynthesis). Because they
need sunlight, they can only live in the photic zone. Through photosynthesis, phytoplankton
make food for themselves and give off oxygen, which is a waste product for them but essential
forallanimals onEarth. Phytoplanktonproduceall thefoodat thebottom oftheocean food
chain, so they are called primary producers. Most of the photosynthesis on Earth happens
in the oceans and phytoplankton produce a large share of the oxygen in the air we breathe.
Zooplankton, or animal plankton eat phytoplankton as their source of food. They can be
found in all parts of the ocean.
Figure 14.28: Plankton are perhaps the most important part of the food chain because they
supply food for most aquatic life. ( 23 )