Marty Adams, age 13, of Cumberland, Md., for his question:
CAN PLANTS AND ANIMALS LIVE ANYWHERE IN THE OCEAN?
Both plants and animals live in the ocean. Plants can be found wherever there is sunlight on and near the surface, in shallow waters and along the shores. They do not live in deep, dark waters. Animals, however, dwell everywhere in the sea.
All life in the ocean can be divided into three groups: the plankton, the nekton and the benthos.
The plankton consists of plants and animals that float about, drifting with the currents and tides. The nekton is made up of animals that swim freely in the water. The benthos consists of animals and plants that live on or in the ocean bottom, from the shore to the greatest depths.
Most of the floating, drifting plants and animals called plankton of the sea can be seen only under a microscope. The plants make up the phytoplankton and the animals make up the zooplankton.
Sea plants get their energy to grow from the minerals in seawater and from sunlight. In most places, the sun's rays do not go deep into the water and plants can't grow there. In clear tropic seas away form muddy rivers, however, light may reach several hundred feet into the ocean. Where you find light, you'll find plants.
The animals of the nekton can swim about. There are over 20,000 kinds of fishes that live in the sea. They range in size from sharks 50 feet long to gobies less than one inch long. The nekton also includes whales, seals, octopusses and squids.
Some sea animals can live under much water pressure because the pressure inside their bodies equals the water pressure outside.
Animals that dwell on the bottom of the sea include worms, snails, clams, sponges, sea lilies and starfish. Ocean currents carry food to these animals.
The phytopiankton is the food base for the animals in the world ocean. Certain animals of the zooplankton eat these plants. These animals, in turn, are eaten by other members of the zoopiankton or by fish or other swimming animals. Generally, larger animals eat smaller animals.
After the animal dies, it begins to sink. Before most dead animals sink very far, they are eaten by creatures that dwell at lower depths. When these animals die, they become a source of food for animals that live even deeper.
Animals begin to decompose or decay as soon as they die. This decomposition takes place at all depths. In addition, animals give off waste products. These waste products, and dead animals that are not eaten, are broken down into mineral salts by tiny living things called bacteria.
Rising currents carry these minerals to the ocean surface, where plants of the plankton use them as food.
Thus, the food cycle in the sea goes on and on.