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Tiny creatures live in Earth’s oceans. Acid waters may wipe them out.

What is in a scoop of seawater? Even in a small scoop, loads of living things splash around. Most of these creatures are small. You cannot see them with your eyes.

To see them, you need a microscope. Then you can watch tiny critters darting about. They are called marine microfauna. They are the smallest animals in the ocean.

These wee creatures fill the sea. Yet they are in trouble. Look inside their world to see why.

Four oceans cover most of Earth. They are the Pacific, Atlantic, Indian, and Arctic Oceans. Together, the four oceans are twice the size of dry land.

The oceans have many habitats. Those are places where plants and animals live. Colorful coral covers some spots. Other areas have forests of kelp. It is a kind of plant.

In each layer of water, you find different animals. Sunlight warms the ocean surface. Sharks and rays live near the surface.

Little light reaches below 200 meters (656 feet). So the water is colder. Yet some animals like that. Whales and giant squid swim in deeper waters. Anglerfish live in some of the deepest waters. The marine microfauna are everywhere.

All sorts of bitty beings float around the oceans. Some have shells. Others are like drops of jelly.

Some are not what they seem. Take the blue button. With many arms, it looks like a flower. Yet one blue button is really many animals together. Each arm has a job. Some arms catch prey. Others eat the prey.

Not all wee critters in the sea stay small. Some are baby sea creatures. They grow up. They get bigger!

All sea life is part of a food chain. A food chain is made of plants and animals that eat one another.

Many larger animals eat marine microfauna. The huge whale shark does. It takes a giant drink of water. It then pushes the water out of its body. The water flows through its gills.

As the water moves, the shark filters out tiny animals in it. The shark then eats them. Fish that eat this way are called filter feeders.

Today, tiny sea animals face a new danger. It is carbon dioxide. That is a gas you cannot see. Cars make this gas. Factories do too. The gas then rises into the air.

The ocean soaks up some of the carbon dioxide. That causes trouble. You see, the gas makes acid when it mixes with water.

Acid can hurt ocean animals. Some animals' shells are too soft. Other sea animals' skeletons are too weak.

You see, what we do on land affects the sea. That may seem hard to believe. Yet it is true. Our actions can help or harm Earth’s water wonders.

Article by Fran Downey. Top-of-page photo by Ingo Arndt/Minden Pictures. "Water Wonders" appears on page 2 of the Nov.-Dec. 2007 issue.