Ahnfeltia plicata
This lower intertidal alga has stiff and wiry branches. A few red algae are the sole source of agar, a gel-like polysaccharide that is widely used in hospitals and research laboratories to grow bacteria. Although not a commercial source, Ahnfeltia plicata contains agar in its cell walls, giving it a characteristic texture. Present year round.

Photos by Joseph Stachelek.

Bangia fuscopurpurea
Bangia fuscopurpurea is an unbranched filament that is found in masses high in the intertidal zone. These red algae have fossils that date to 1.2 billion years old and are among the oldest known fossils of advanced (eukaryotic) multicellular organisms. Present winter–spring.

Photos by Sarah Hall.

Ceramium rubrum
Ceramium rubrum has pincers on the ends of its filamentous branches that can be seen with the naked eye. This red alga is abundant in the lower intertidal zone. Present nearly year round.

Photos by Joseph Stachelek.

Chondrus crispus
This red alga (“Irish Moss”) is found in the lower intertidal and shallow subtidal zones. It is a common source of carrageenan and is still harvested commercially on Prince Edward Island (Canada). The polysaccharide carrageenan is extracted from cell walls and forms a gel that is used commercially as a thickener (e.g., in ice cream). Chondrus turns white when exposed to freezing low tides in winter or very hot low tides in summer. Present year round.

Photos by Joseph Stachelek.

Corallina officinalis
Corallina officinalis is found in the lower intertidal zone, especially in tidepools. It feels hard because it is calcified; calcification may prevent herbivores from eating the alga, and calcification is hypothesized to increase photosynthesis. Calcifying algae are under threat from increasing acidity in oceans due to carbon emissions from cars and factories. Present year round.

Photos by Joseph Stachelek.

Cystoclonium purpureum
This red alga is found in the lower intertidal and shallow subtidal zones and is most abundant in summer. Cystoclonium purpureum sometimes grows on other coarse algae and is shown here on a bed of Corallina officinalis (see entry for Corallina). Present year round.

Photos by Joseph Stachelek.

Devaleraea ramentacea
Devaleraea ramentacea is only able to survive in waters that are colder than 15°C. This alga becomes abundant in the lower intertidal (including tide pools) and in shallow subtidal zones. Common in winter-late spring.

Photo by Joseph Stachelek.

Dumontia contorta
Dumontia contorta can be identified by its overall twisted structure. This alga is most abundant in tide pools and the lower intertidal zone. Present winter–late spring.

Photos by Joseph Stachelek.

Mastocarpus stellatus
Mastocarpus stellatus looks similar to Chondrus crispus but has higher tolerances to physical stresses, including freezing and drying. Consequently, it is most abundant near the borders of the mid- and low intertidal zones. It also grows in pools in the high intertidal zone. Females of Mastocarpus stellatus are typically covered with distinctive bumps, giving the blades a rough texture. Present year round.

Photos by Joseph Stachelek.

Membranoptera alata
Membranoptera alata grows as small, flattened, and alternately branched blades with distinctive midribs. Reproductive in winter to spring, this alga can be found growing in tide pools and in the shallow subtidal zone. The dark balls on the blade are reproductive structures called tetraspores. Present year round.

Photos by Joseph Stachelek.

Palmaria palmata
Palmaria palmata (“dulse”) is a traditional food in maritime North America that is used in condiments, soups, and appetizers. Dulse is found in the lower intertidal and shallow subtidal zones. Sometimes it grows on other algae. Present year round.

Photos by Sarah Hall.

Plumaria plumosa
Plumaria plumosa is characterized by delicate branching. The Latin word “plumosa” describes this species as feathery. This red alga is found in the lower intertidal zone and tide pools. Present year round.

Photos by Joseph Stachelek.

Polysiphonia lanosa
Polysiphonia lanosa is a branched, filamentous alga that is very common in the mid-intertidal zone growing on Ascophyllum nodosum. Dark balls (see microscopic photograph) found in several upper branches of this alga are reproductive structures called tetraspores. Present year round.

Photos by Joseph Stachelek (left) and Sarah Hall (pop-up).

Polysiphonia stricta
This delicately branched alga is found in lower intertidal and tide pool habitats. Every branch has an inner, straw-like filament (see microscopic photograph). Present in winter–spring.

Photos by Joseph Stachelek.

Porphyra amplissima
Porphyra amplissima grows up to a meter long and is found in the low intertidal and shallow subtidal zones. In Asia, other Porphyra (“nori”) species are important aquaculture crops; nori harvested for human food is worth about $1.2 billion a year. Present spring–early summer.

Photo by Joseph Stachelek.

Porphyra umbilicalis
Porphyra umbillicalis (“purple laver,” “nori”) is most common in the mid-intertidal zone. Its irregularly-shaped, reddish-brown blade is edible. Porphyra umbilicalis is very resistant to drying during low tide and contains natural UV sunscreens. This red alga turns green in summer because of low nutrients and exposure to temperatures above its tolerance level at low tide. Present year round.

Photos by Joseph Stachelek (left) and Nic Blouin (pop-up).

Rhodomela confervoides
The upper portions of Rhodomela confervoides are densely branched. When present, this red alga is common in tide pools. It contains bromophenols, which are compounds that have antibacterial properties. The scale bar to the left of the photo is 7 cm long. Present late winter–mid-summer.

Photo by Joseph Stachelek.