Tidepools are pockets or pools of ocean water trapped in rocky ledges after the tide has gone out. Low Tide happens twice a day around Mount Desert Island and Acadia National Park . In order to explore this small world, you have to time your visit just right, as it’s only possible to safely visit this small world about 2 hours around low tides. However one of these will most likely be at night, so really there is only one chance each day. This next week these are the times you can visit the tide pools.

So if you are visiting this week, you have some great middle of the afternoon time
between 2:00 P.M. and 5:00 P.M. to visit a tide pool. This low tide time will keep cycling about an hour later each day, so check on the best time for you right before you plan on your visit.
Second, you need to be careful, as this environment is often slippery. Wear sturdy shoes with good gripping soles. If you bring a see-through container with you and fill it with cold ocean water, you can observe some of these creatures from the bottom up.
The facts in this article came from a book called Discovering Acadia A Guide for Young Naturalists By Margaret Scheid A copy for you to read yourself can be found at SeaCat’s Rest.
The most numerous creatures there are the barnacles. They are one of the first things you will step on while looking for a tide pool. If you look at them closely, they resemble tiny volcanoes. Their shells are grayish white with sharp edges, and they cement themselves permanently to rocks (they are at the bottom of this collection of shells photographed at our shore) . If
you want to see them in action, look for a tide pool where they will be under water. If they are not “out” swish the water a bit with your hand for a few seconds and they come out to eat the plankton (microscopic food) that you have stirred up. Out of water their shells are closed up tight, in the water they use six pairs of feathery legs to sweep food into their mouths.
The next creature most abundant are the Dog Whelks. Looking like a snail with a pointy end, Whelks are carnivorous animals that love to eat the barnacles. They have a drill like tongue called a radula (rad-you-la), it lets them bore through the shells of the animals they
like to eat. Their shells come in many colors and patterns.
Mussels will be found often too numerous to count, other times, hardly there. They have black shells and are also vegetarians, feeding on plankton, but they use siphons to filter their food from the water. They act like straws, bringing in sea water. As long as they are under water and not disturbed, you can watch them feeding through the two siphons. Under crashing waves, they attach to rocks with their strong Byssal (Bis-all) threads to hold them in place. Adult mussels can be up to 4 inches long. Mussels also get eaten by
those dog whelks you read about just before this paragraph, look for a small hole in a shell and you know what happened. Mussels are also fed upon by starfish, who may look pretty, but attack shell fish just the same. This picture is a batch of baby mussels. For scale, the shiny thing in the picture (to the left) is a quarter.
Have you found any green or brown weeds that seem to be growing on rocks? Look in the picture with the quarter. That is Rockweed. There are two kinds around here. The Knotted Wrack, which looks like a rope with hollow bumps or knots called air bladders (on the left in the picture). And the Bladder Wrack which has air bladders too but flat branches (on the far right). Like most seaweeds they have no roots. They absorb the water, carbon dioxide and nutrients they need through their surface. Through the process of photosynthesis (fo-toe-sin-tha-sis) the rockweeds use the sun’s energy to make their own food. The bright green item in the little mussel picture is another kind of sea weed called sea lettuce.
Sea Stars would be rare to find in a tide pool, but if you kayak in front of SeaCat’s Rest at low tide (or out by the big rock around Old Point) you will find them hanging out on the sea floor. Mussels are among their favorite foods. They have to work hard to get that shell open, they squeeze the shell really hard, and get one of their feet inside and then eat the sides of the shell for dinner. The big spot on top is called a madreporite (Mad-ra-por-ite). This opening lets water in and out of a sea stars’ many tube feet so they can move around. The underside of each foot has many tubes that help sea stars grab onto things and move about, or stay in one place as they wish.
The green round spike thing you might see is called a sea urchin. Of course, while they look scary, they are not mean. They have tube feet like their cousins the sea stars. While they are under water, their feet often stretch out beyond the spines, holding on to rocks and helping the sea urchin to travel. After they die the sharp spines fall off and a beautiful delicate shell, called a test is all that is left. At sand beach in Acadia National Park, the sand includes many broken green spines, see if you can find a few. Gulls love to eat the insides of sea urchins-and so do sushi lovers. Look for five, white teeth underneath. They’re great for eating seaweeds and animal remains.
Periwinkles. Called ‘Winkles” you find them just about everywhere in the tide pools. They are vegetarians, that eat plants, especially algae (Al-jee) that they scrape from rocks with a radula (file-like tongue)
You can tell winkles apart from the carnivorous dog whelks by a teardrop shaped opening. Look carefully. If you touch a winkle, they will retreat into their shell. All you’ll see is a door-like operculum(o-pur-cue_lum) which keeps the animal inside moist and protected. There are three kinds of Periwinkles in Acadia. Common Periwinkles, Smooth periwinkles and rough periwinkles (above high tide) The biggest are the common periwinkles.
Limpets are vegetarian snails too. Because of the shape of their shell they are also called chinaman’s hats. They have one shell and no protective operculum like the periwinkles. Instead, their foot acts like a suction cup, holding on tightly to rocks. This keeps limpets from drying out at low tide, or getting knocked around at high tide.
Last but not least are the crabs. Look for them under rockweeds and boulders, hiding from hungry sea gulls. There are four kinds of crabs around here. Rock
crabs, have a smooth-edged shell. Jonah crabs have a rough edged shell, green crabs, and hermit crabs that live in the empty shells of snails after they die. As they grow, they look for bigger shells.