This story was originally published in August 2020.
As the tide ebbs from Maine’s rocky coastline, pockets of saltwater are left behind, filled with a wide variety of aquatic creatures and plants. These tide pools present the perfect opportunity for people to easily observe ocean life. They’re like little natural aquariums, rearranged with each new tide.
“They’re everywhere along the Maine coast,” said Helen Hess, an invertebrate zoologist and professor at College of the Atlantic. “Tide pools offer a refuge in the intertidal zone for those things that prefer to always be underwater.”
Exploring these pools — an activity known as tide pooling — is a fun and educational pastime that’s especially popular among children. If you give it a whirl, here are a few creatures you may encounter.
Barnacles
One of the most common tidal pool animals in Maine, the barnacle is often overlooked because it’s tiny and immobile. Encased in a rough, circular, white shell, this small crustacean glues itself to rocks and other submerged objects, usually in the company of other barnacles. When tide pooling, you may find them in or out of water.
“Barnacles are masters at being able to tolerate those really challenging conditions up in the high intertidal zone,” Hess said. “Often you’ll find them high and dry, and they’re all closed up so they don’t dry out.”
They also close up to regulate their temperature, Hess explained. But when under the water — say in a tide pool — they will often open their shells and sweep their legs through the current, ushering plankton (tiny, floating organisms) into their mouth.
“If you see one feeding, you’re lucky,” Hess said. “You have to know what to look for and be a little patient.”
Blue mussels
Encased in teardrop-shaped shells, blue mussels are mollusks that are abundant along the Maine coast in intertidal and shallow, subtidal zones. They’re also a delicious offering on any Maine seafood menu.
Typically found growing in clusters, mussels attach to rocks, the ground or other stable surfaces with strong threads of protein.
“Mussels attach with these little threads made of protein,” Hess said. “If you’ve ever cooked mussels, often the beginning part of the recipe says to debeard mussels, and that’s the little attaching fibers.”
Periwinkles
Snails that graze on algae growing on rocks and seaweed, periwinkles are especially abundant in tidepools. This creature is also referred to as winkles or wrinkles, and harvesting them is sometimes called “wrinkling.”
In Maine, periwinkles are considered invasive species, having been brought to North America from Europe, according to a National Oceanic and Atmospheric Administration report on molluscan fisheries. They were first reported in the Bay of Fundy in the mid 1800s.
Dog whelks
Another snail found in Maine tide pools are dog whelks, which are carnivorous and commonly eat barnacles and baby mussels, Hess said. Both periwinkles and dog whelks create round, coiled shells, but the dog whelk shell is longer and more pointed. Their shapes — like their diets — are distinctly different.
Limpets
Another type of snail, the limpet lives in a wide, conical-shaped shell and slowly cruises over rocks, feeding on algae.
“They love to graze on coralline red algae, which looks like pink paint [on rocks],” Hess said. “It’s actually seaweed, and the way it protects itself from grazers is to have minerals embedded in the tissue that makes it really hard. There’s almost no grazer that has a mouth strong enough to eat it. Limpets are exceptions.”
Limpets are often difficult to pick up because they can clamp down onto a surface using a wide, muscular foot and mucus. This ability can protect them from predation, being knocked around by waves and — if stuck out of water — it can protect them from desiccating in the sun.
Sea stars
Also known as starfish, sea stars are one of the most recognizable creatures of the ocean. With colorful, star-shaped bodies, they cling to hard surfaces such as rocks and can often be found in both shallow and deeper water.
Throughout much of the world, including Maine, sea star populations have suffered in recent years due to disease.
“They’ve definitely had some population booms and busts over the years,” Hess said. “It varies geographically where you can find them in Maine, but they’re definitely found in tide pools. They love to munch on mussels.”
Sea urchins
A close relative of the sea star, urchins live in round, spiny shells that are hard to miss. Like the sea star, they move using tiny tubed feet, and you can turn them over to see the mouth at the center of their body.
“They are herbivores typically,” Hess said. “What they like to do is graze seaweed. If you look at the mouth of the sea urchin, you can see five little white teeth in a circle.”
Green crabs
The most common type of crab you’ll find in a tidal pool is a green crab, Hess said, though they’re not always green. In fact, when young, green crabs display a wide variety of colors and patterns on their shells. A lively and colorful tide pool creature, green crabs are actually considered to be invasive animals in Maine, and they feast on some of our most prized shellfish.
If you want to confirm that a crab is a green crab — rather than a rock crab or Jonah crab (two other Maine varieties) — count the little points along the front edge of its shell. If there are five points between the middle of the shell and the corner, it’s a green crab, Hess said. As you count the points, just think GREEN.
Hermit crabs
Another active tide pool creature, the hermit crab is a small crustacean that shelters itself in empty shells left by other animals such as periwinkles or dog whelks. They’re fascinating to watch as they crawl about, dragging their shells with them.
If you gently pick one up, don’t worry about it losing its shell home. Its soft abdomen is curled around the contours of the shell, keeping it securely in place. But watch out, it might pinch you with its front claws (one of which is notably larger than the other). You can often spot these animals interacting with each other. They even steal each other’s shells.
Rock gunnel
An eel-like fish found in tidepools, rock gunnels can often be found burrowed under rocks or seaweed. They can even survive outside the water for a period of time because their slimy skin prevents them from drying out. Also, they breathe through their skin.
“They’re about 4 to 6 inches long and very eely looking,” Hess said. “When you find them, they can panic and start flipping and flopping around, but if you keep your hands wet, you can hold onto it [for just a moment] and check out its cute face.”
How to tide pool responsibly
Acadia National Park offers guidelines for tide pooling responsibly, which includes washing sunscreen, hand sanitizer and bug spray off before dipping your hands in tide pools. This will minimize the exposure of harmful chemicals to marine life. In addition, observe tide pools from their edges rather than stepping or sitting in the water itself. This way you avoid tramping on the animals inside the pool.
If handling tide pool animals, it’s important to do so gently and place them back where you found them. In many cases, you’ll see more of their natural behaviors if you don’t touch them at all.
“Be patient and just sit there for a bit,” Hess suggested. “It may look like nothing is going on in the pool at first, but all kinds of things are going on — it’s just happening at a more mellow pace than we’re used to.”
Tide pools are found all along the Maine coast. Next time you visit the ocean at low tide, seek one out. Even the smallest saltwater pool can be home to a wide variety of creatures.
