Tidepools form where pools of water collect in rocky hollows at low tide. There are easier places in the ocean to survive. Tides, temperature, saltiness--all these are constantly changing. Only hardy animals can survive in the tidepool. Most of them are animals without backbones--invertebrates--which are fairly simple compared to other kinds of sea animals, such as fishes and whales. A crab, for example, can grow back a lost claw. A starfish cut in half might grow back into two starfishes! How many fishes can do that?
Three basic laws of survival rule life in the tidepool:
- keep from being washed away by the waves at high tide
- keep from drying out by the sun at low tide
- keep from being eaten
The plants and animals which live near the top of the tidepool are the toughest. Bright green sea lettuce grows well in the saltiest puddles of the tidepool. Barnacles can stay wet inside their volcano-shaped shells for days at a time. When the water returns, they open up their shells to kick food into their mouth with their feathery feet. Brown periwinkles graze on algae, while white dog whelks use acid and a sharp tongue to drill through the shells of other snails.
Brown rockweeds drape the middle zone of the tidepool. Air bladders let them float on the surface of the water at high tide where they can get the best light. Beneath the seaweed starfishes and sea urchins cling to the rocks with sticky tube feet. Mussels hold on with lifelines they weave themselves. Just below them grows a red seaweed, Irish moss. It was once collected along the coast of Maine with long-handled rakes. It was used to thicken puddings, ice cream, milk shakes, and toothpaste. Green crabs wander throughout the tidepool, always looking for a chance to grab a meal. They keep close to cover, though, to avoid being noticed by a sharp-eyed herring gull. In the lowest tidepools, sea anemones, sponges, and baby lobsters find shelter under the swaying fronds of brown kelp.
Tidepools give us land dwellers a chance to peak at the daily lives of ocean animals: hunting, eating, fighting off predators, clinging to the rocks against the force of the waves. Each retreat of the tides reveals a miniature ocean world. Sit quietly by the edge of a tidepool and wait for its secrets to open up to you.
Collect enough periwinkles for each student in the class. The snails will keep well over night if stored in cold seawater. Each student gets his or her own periwinkle. Observe differences in color,size, shape, dents in shell, "personality". Some periwinkles open their trap doors (operculum) when you hum to them. After a time, return all periwinkles to one or two containers. Each student must now find his/her own. How could they tell the difference? It is surprising how different individual periwinkles can be, even though initially they all looked the same.