Michael Meyer, age 12, of Staten Island, N.Y., for his question:

WHAT ARE TIDAL POOLS?

We find them on beaches where chunky boulders squat half hidden in the sand. When the high tide floods in, the rocks are hidden under water. When the low tide drains back to seas puddles of water are left behind among the rocks to form these salty tidal pools.

The earth provides a variety of homes for plant and animal communities. There is suitable greenery for assorted herbivores, and enough predators to control their populations. All the plants and animals in a given environment depend upon each other. There are ecosystems of this sort in valleys and deserts, on mountains and plains. And, though all the world oceans merge together, there are different ecosystems in zones of the sea.

In the deep ocean, life is a frantic chase, for every creature is a hunted hunter. The survivors must be fast or cunning. But on a rock strewn beach, the harsh environment changes every six hours. When the tide goes out, assorted sea dwellers are stranded in pools of water left behind among the rocks. And there is no escape.

A tidal pool is home to a colorful variety of plants and animals. A clump of mussels in dark blue shells clings to a rock with golden threads. They vie for space with rock clinging barnacles. There are crusty crabs and prickly sea urchins, snails and starfish, slugs and worms. The plankton rich water teems with microscopic algae; wads of seaweed anchor their toes to the stones.

High tide floods the neighborhood under several feet of water, and the populations have a few hours of frantic activity. The mussels part their purple shells to let the water bring in oxygen and scraps of food. Hungry starfishes prey on their neighbors.    Many creatures    feast on plankton and on each other. Then the tide turns and most of the water runs back to the sea.  

All these creatures depend on salty sea water, and each species copes with the shortage in its own way.  The mussels shut their shells to conserve the moisture inside. Crabs and snails, starfish and a host of others seek to hide themselves in moist pockets among the seaweeds and under the rocks.

Each dweller in a tidal pool adapts and adjusts his behavior with the changing tides. And strange to say, his way of life continues even when he is moved to a non tidal environment. When moved to a calm, deep water aquarium, every six hours he prepares himself to cope with a changing tide.