The different zones of the rocky intertidal
The intertidal zone is the broad band between the high and low water marks. On a rocky shore, when the tide is high, one might assume that nothing at all lives on or around these rocks, for nothing is visible. When the tide is ebbing, however, the rocks that the high tide had concealed comes into view, and are visibly marked by horizontal belts or colonies of similar species adapted to a twice daily exposure to air and sea, living where conditions for survival are best for them. The three most conspicuous zones – the barnacle zone, the rockweed zone, and the red algae zone – are described below:
“Like drifts of old snow no longer white, the barnacles come into view; they blanket rocks and old spars wedged into rock crevices, and their sharp cones are sprinkled over empty mussel shells and lobster-pot buoys and the hard stipes of deep-water seaweeds, all mingled in the flotsam of the tide.”
“Meadows of brown rockweeds appear on the gently sloping rocks of the shore as the tide imperceptibly ebbs. Smaller patches of green weed, stringy as mermaids’ hair, begin to turn white and crinkly where the sun has dried them.”
“In the calm world of the deeper rock pools, undisturbed by the tumult of incoming waves, crabs sidle along the walls, their claws busily touching, feeling, exploring for bits of food. The pools are gardens of color composed of the delicate green and ocher-yellow of encrusting sponge, the pale pink of hydroids that stand like clusters of fragile spring flowers, the bronze and electric-blue gleams of the Irish moss, the old-rose beauty of the coralline algae.”
- Rachel Carson, The Edge of the Sea
The geology of Maine’s shores
During the Devonian Period (some 350 million years ago) the New England region was monotonously level, as the highlands had all been eroded away. Then, in several places along the coast of Maine, large masses of molten granite and other igneous rocks pushed slowly toward the surface through vents in the earth’s crust.
Over the millions of years since then, erosion has again leveled much of coastal Maine into a flat plain with wide beaches of sandstone and shale. Behind these beaches lays a landscape of rocky hills and valleys formed of crystalline rocks highly resistant to erosion, of which only the hard rock, mostly granite, remains today.
When the last glacier, known as the Laurentide Ice Sheet, passed during the Wisconsin Stage (about 18,000 years ago), the landscape changed once again. This vast continental glacier spread south from north central Canada, covering the coast of Maine and causing the flexible crust of the earth to tilt downward. As the northern coastal plain was pressed down into the earth, the sea ran far up between the hills and occupied the valleys. As the glacier melted, it left behind polished rock, steep cliffs on mountain faces, and many large boulders. The characteristic indentations and irregularities along the coast of Maine are therefore the result of crustal down-warping and the great weight of the ice.
So how did the beaches of sand, pebbles and cobblestones form on this predominantly rocky coast?
The origin of these beaches is in the glacial debris that covered the rocky surface when the land tilted and the sea came in. Boulders, pebbles, sand and shell fragments were carried in by strong waves from deeper water, which cast them onshore to form beaches. Notice that the sandy beach across from Oceanside Meadows is in a protected incurving inlet, where the waves can deposit debris but cannot easily remove it. Also, notice that the rocky shore is formed primarily of pink granite, a hard rock that has resisted thousands of years of erosion.
Algae are primitive organisms without true roots, stalks, stems, or leaves. Instead, they have cells that serve as root-like structures that enable them to cling to rocks and to resist removal by tides and waves. They fall into 3 groups, or phyla. Here are examples of species that you may come across as you explore the rocky shore at Ocean Meadows:+
The Green Algae: Phylum Chlorophyta
* Sea lettuce (Ulva lactuca) is one of the most familiar shallow water seaweeds. It grows in a variety of places ranging from exposed rocks to quiet pools. It is tolerant of moderate pollution and is edible.
* Green fleece (Codium fragile) This distinctive plant lives in the shallow water of sounds and bays but often washes ashore in heavy, ropy masses, dragging along pebbles and shells. It has a choking effect on shellfish.
* Hollow green weeds (Enteromorpha sp.) These species occur in a variety of habitats. They are most common on rocks in lower intertidal zones. They have a wide tolerance for varying and greatly reduced salinity and can penetrate deep into estuaries.
The Brown Algae: Phylum Phaeophyta
* Rockweeds (Fucus sp.) The brown rockweed is one of the most widely distributed plants in cool waters near rocky shores. It has swollen air bladders along its midrib to keep it upright at high tide. Many tidepool creatures hide from their enemies in rockweed. The broken parts of the plant continue to grow and reproduce, increasing the density of vegetation in a pool.
* Knotted wrack (Ascophyllum nodosum) Long fronds of this olive-colored weed cover intertidal rocks below the upper band of rockweeds. When exploring any expanse of rock covered by this slippery weed, keep in mind that you are walking over a thick bed of wet noodles concealing sharp rocks, deep crevices, and other pitfalls.
* Edible kelp (Alaria sp.) Kelps are large brown algae, common to cooler waters. They are valued for fertilizer because they contain large amounts of minerals. Many tons of kelp are harvested each year, and some are used for food.
The Red Algae: Phylum Rhodophyta
* Irish moss (Chondrus crispus) ranges in color from deep purple to green. This algae is common in tidal pools and is a valuable part of the food chain. It is also gathered commercially because it is used for making industrial chemicals and food products such as ice cream and gelatins.
*Coral weed (Corallina officinalis) ranges from pink to red, and precipitates calcium and magnesium carbonate as a hard surface crust. When it washes onto beaches or into tidal pools, the sun bleaches it completely white.
* Crustose algae (Hildenbrandia prototypus) The encrusting algae produce vivid colors and “tar spots” in tide pools and on wave-washed rocks. Hildenbrandia prototypus is common and conspicuous in pools and on intertidal rocks and shells. Look in tidepools for this bright red encrusting algae on the rocks.
Barnacles: (Balanus balanoides)
The barnacle’s shell of calcareous plates conceals a shrimp-like animal glued down by the top of its head. When covered with water, the barnacle rhythmically opens and closes its trapdoors to extend its feathery cirri like a small hand, grasping blindly for any planktonic morsels adrift in the water. Most barnacles are hermaphroditic (both male and female at the same time), but they indulge in cross fertilization. Watch your step when you walk on the rocky shore, as the barnacles can cause painful cuts.
Snails: Periwinkles (Littorina sp.)
Periwinkles abound in tidepools. These snails are mollusks and are related to clams and mussels. Their soft bodies are covered by mantles, which secrete the hard outer shell. Periwinkles are gastropods, which means “stomach–footed”. Their heads and feet extend beyond the fronts of their spiral-shaped shell. Periwinkles are vegetarians and browse on algal films and the like. They can withstand long periods without food or water.
Mussels : Blue mussel (Mytilus edulis)
Mussels are two-shelled mollusks. Their bodies are very soft, but have the ability to build hard shells that protect them from predators such as starfish, crabs, and sea gulls. Blue mussels, the most common of the species, are found in tidepools, where they attach themselves to rocks by strong threads. These mollusks tend to live in clusters and large colonies.
Sea Urchins: Green sea urchin (Strongylocentrotus drobachiensus)
Sea Urchins belong to the phylum Echinodermata, which derives its name from the Greek words ‘echinos’ and ‘derma’, meaning “hedgehog skin”. The sea urchin has a globular body covered with movable spines. Their skeleton consists of close-fitting calcareous plates forming a rigid shell, or test. Sea urchins possess a unique internal plumbing system known as the water vascular system. By varying the internal water pressure, the urchin can extend or contract its tube feet, which are used in locomotion, food collection, and respiration. In Northern New England, the Green Urchin is the most prevalent of sea urchins. It is often found in tidepools and below the low-tide line, where it is preyed upon by birds, sea stars, cod, and lobsters.
Lobsters are among the most popular marine animals. Lobster are crustaceans: joint legged animals covered with shells. You may find a young lobster scavenging for food at the bottom of a tidepool. The North Atlantic lobster has a hard exterior shell – called an exoskeleton – that surrounds and protects its body. Its two front legs are actually claws. They have one large crusher claw and one smaller claw for transferring food to its mouth. It has five pairs of legs, two pairs of antennae (or feelers) and a tail with broad, scaly plates on the end. It uses its fanlike tail to move about.
Crabs: Green Crab (Carcinus maenus)
Like the lobster, crabs are also crustaceans. They are common residents of tidepools, where they lurk among the seaweeds or crawl over the rocks. A crab is easily identified by its upper shell, called carapace. As crabs grow, they periodically shed their old shells and grow new ones. Like other crustaceans, crabs are scavengers, and eat decaying plant and animal matter, though they sometimes prey on small animals, including clams and mussels. The Green Crabs have yellow spots and five tooth-like serrations on each side of the front of their shells. You most likely will find them under stones or among seaweeds in tidepools.
Thick falls the dew, soundless on sea and shore:
It shines on little boat and idle oar,
Wherever moonbeams touch with tranquil glow.
The waves are full of whispers wild and sweet;
They call to me, – incessantly they beat
Along the boat from stern to curvéd prow
Comes the careering wind, blows back my hair,
All damp with dew, to kiss me unaware,
Murmuring “Thee I love,” and passes on.
Sweet sounds on rocky shores the distant rote;
O could we float forever, little boat,
Under the blissful sky drifting alone!
- Celia Thaxter
Please visit this new site again where we hope to show you more of Oceanside Meadows and our local area.
For further information please do not hesitate to call us here on the coast of Maine. We look forward to welcoming you.
Oceanside Meadows Inn P.O. Box 90, Prospect Harbor, Maine 04669
Tel: (207) 963 5557 Fax: (207) 963 5928 Email: email@example.com
The painting on this page is by Deane Folsom, an award winning painter whose work we are glad to feature here and in our inn. Absolutely all proceeds from the sale of Deane’s work go directly to support the artist and his work.