Shirley Hachiuma, age 11, of Prescott, Ariz., for her question:
WHAT IS PLANKTON?
Various tiny sea animals and plants are called plankton. These tiny organisms play an important role in the life of the seashore. They swim or float on the ocean tide.
The name plankton comes from the Greek word for wandering. The plankton consists mainly of small animals such as protozoans, larval fishes and crustaceans, but also includes some larger ones, such as jellyfish.
During the day, the plankton animals usually swim as deep as 1600 feet below the surface. But at night, they rise to the upper levels of the water.
The plankton also consists of tiny plants, such as algae. There are three groups of drifting plant life: the diatoms, the peridinians and the coccospheres.
Plankton is important food for larger animals, such as herring, mackerel and whales.
The life on the bottom of bodies of water is called benthos. The animals of larger size that swim freely, and independently determine their movements in the body of water, are called nekton.
Most large seashore animals start their existence as larvae, plankton creatures that bear little resemblance to their parents. Most spores and larvae die, but some land on a suitable shore and grow into adults.
Plankton serves as more than a nursery for seashore life. As the ocean waves sweep across the shore, they carry with them a feast of plankton. Many seashore animals feed on these tiny organisms. Such creatures as barnacles, mussels, oysters and sponges spend their adult life permanently attached to the shore. They eat the plankton when it comes to them.
Other animals, including clams and worms, burrow into the shore and collect their food from the water containing plankton.
Even the various shore birds that feed on the plankton eating creatures rely on plankton.
Scientists classify seashores into three main types, depending on their surface: rocky shores, including coral reefs; muddy shores; and sandy shores.
Life on rocky shores is more plentiful than on any other type of seashore. Great numbers of animals and plants crowd the hard, rough surfaces of coral reefs and wave scarred cliffs.
Most animals that live on rocky shores eat plankton.
Most muddy seashores lie in bays, protected from strong waves. Rivers empty into many such bays, decreasing the saltiness of the sea. Land plants, including various grasses, thrive among muddy shores. Crabs and turtles live among these plants. Clams and various worms burrow into the muddy bottoms.
Life on sandy beaches is not as plentiful as it is on rocky or muddy shores. Most plants and animals cannot attach themselves strongly enough in the loose sand to withstand waves and currents. Most of the animals of sandy shores burrow under the sand. Few plants live on sandy shore between the levels of high and low tide.