Living Filters: The Science and History of Sea Sponges

Living Filters: The Science and History of Sea Sponges

1Picture a creature with no brain, no heart, no stomach and no muscles. It cannot walk, swim or chase its food. For most of its life, it stays fixed in one spot on a rock or reef. You might guess it is a plant, but it is an animal. It is a sea sponge, one of the simplest animals on Earth.

2A sponge's body is covered with tiny holes called pores. In fact, scientists group sponges under a name that means "pore bearers." The pores lead to a maze of channels and small rooms inside the sponge. Many sponges live in the ocean, and a smaller number live in lakes and rivers.

3Because a sponge cannot move to find food, the food must come to it. Special cells line the inside of the sponge. Each of these cells has a tiny whip-like hair. When the hairs beat back and forth, they pull water in through the pores. As the water flows through the channels, the cells trap bits of food, such as bacteria and tiny pieces of dead plants and animals. Finally, the cleaned water flows out through a larger opening, often near the top of the sponge. Because sponges strain so much water, scientists sometimes call them living filters.

4Sponges matter to the places where they live. By filtering water, they help keep it clear. Their many holes and hollow spaces also give shelter to small creatures, such as shrimp, crabs and young fish.

5A young sponge does not begin life in one place. It starts as a tiny larva that swims through the water. After a short time, it settles on a hard surface and attaches itself there for good. Some sponges can also grow from a broken piece. If a storm snaps off part of a sponge, that piece may land somewhere new and grow into a whole sponge.

6People have used sponges for thousands of years. The ancient Greeks and Romans used them for bathing and cleaning because a dried sponge is soft and holds a lot of water. Later, divers made a living by gathering sponges from the sea floor. In the early 1900s, many sponge divers from Greece moved to Tarpon Springs, Florida. Wearing heavy suits and metal helmets, they walked along the bottom of the Gulf of Mexico to collect sponges. The town became famous for its sponge trade.

7Today, most kitchen and bath sponges are not animals at all. Factories make them from materials such as plastic foam. Still, natural sponges remain important in the ocean, where they quietly clean the water day and night.