Pacific Tide Pool Seaweed & Algae

Low Tide Uncovers Kelp, Sea Palms, Red Coralline Algae, Sea Lettuce

Jun 15, 2008

Forests of sea plants crowd around the edges of pools left behind on rocky Pacific shores when the tide is at its lowest.

Low tide on Pacific beaches of Oregon, Washington and British Columbia reveals a brief view into a world of plants and animals that live most of their lives covered by sea water. Exploring this intertidal zone of tide pools and rocks encrusted with sea life is an extraordinary experience for adults and children alike.

The unusual array of colorful Pacific Coast tide pool animals live amid a forest of plants that wave colorful fronds in the water, stay afloat with air filled balls, or spread out broad damp blades that shelter delicate creatures hiding below them. Some, like sea palms, resemble miniature copies of trees that grow on land; others, like coralline algae, form large colonies, turning the rocks pink or lavender.

Plants of the intertidal zone – that space between high and low tide – must be tough to survive. They must withstand first the inrushing tides, then the twice-daily exposure to fierce salt winds, driving rain or drying sun. Seaweeds cling to rocks with glue-like “holdfasts” that look something like the roots of dry-land plants. Their fronds and blades are strong and leathery to avoid being ripped and torn. Some algae encrust themselves onto rocks to keep from being washed away.

Sea Lettuce, Iridescent Seaweed and Rockweed

Sea Lettuce is aptly named. Called Ulva by biologists, its broad, stemless blades resemble leaf lettuce, though it’s somewhat translucent. The blades feel smooth and slick to the touch. The plant is among the most prolific near the low-tide line.

The “iridescent seaweed” also has a fitting name. It’s distinctive for its changing hues of red, green and blue. It has an oily look and, like most seaweeds, is slippery when encountered on rocks. It is common on the intertidal rocks, hanging limp where water has receded or spreading its blades to float in tide pools.

Rockweed (Fucus distichus) is another common seaweed of the mid-intertidal zone. As the name implies, it typically attaches to rocks in dense mats. Its many flat, flexible brown to olive-colored branches thave air-filled tips.

Kelps

Beachcombing after storms often reveals another common plant that grows just beyond the low-tide line, the bull kelp. These can grow in abundance, forming large kelp beds just beyond the rocky intertidal. They grow on long, stem-like “stipes” that reach to the surface where a bulb-like float keeps them aloft. Long blades wave like banners around the float. Fish and other near-shore creatures find shelter and food in dense kelp beds. When bull kelp lose their grip on the submerged rocks, they often wash ashore scattering across the intertidal rocks.

Giant kelp is similar to the bull kelp, but has multiple small floats. Another, the feather boa, lives up to its name with feathery fringe and small floats.

Coralline Seaweeds and Sea Palms

Common and colorful on many tidepool rocks are several types of coralline algae and seaweed. Colored pink and lavender, these encrust on the rocks, often covering large areas and providing a backdrop for tidepool animals. While not hard like true coral, they have a crusty feel when touched.

Beware of areas where sea palms grow. These seaweeds look just like little palm trees, but they grow where tide is most treacherous and unpredictable. The green fronds cascading from their thick stocks look delicate, but they are tough enough to withstand the fiercest ocean surf, winds and pounding high tides.

Exploring exposed rocks and tidepools at low tide can be exciting. But care is necessary to avoid falling on slippery seaweed and to minimize damage to tidepool plants and animals.

Below are several field guides that can help in identifying specific plants and creatures and enhance your tidepool exploration.

References:

Tidepool & Reef: Marinelife Guide to the Pacific Northwest Coast, byRick M. Harbo (Hancock House Publishers Ltd.)

Between Pacific Tides, by Edward Rickets and Jack Calvin (Stanford University Press). This is a classic of marine biology with more than 600 pages.

The copyright of the article Pacific Tide Pool Seaweed & Algae in Marine Habitats is owned by Linda McDonnell. Permission to republish Pacific Tide Pool Seaweed & Algae in print or online must be granted by the author in writing.