Sanctuary Integrated Monitoring Network
SIMoN Tools

Species Database

Fucus gardneri - Bladderwrack

Bladderwrack image

Geographic range:

Bering Sea, Alaska to Santa Barbara, California

Key features:

The dichotomous branches have a distinctive, raised midrib. When mature, the tips swell and fill with air and mucilage, turning greenish-yellow.

Similar species:

Pelvetiopsis limitata -- Dwarf rockweed; skinny, clumped
Silvetia compressa -- Elongate clumps


bay (rocky shore), exposed rocky shore, protected rocky shore

Primary common name:


Synonymous name(s):

Fucus distichus

General grouping:

Brown seaweed/algae

ITIS code:


Geographic Range

Range Description:

Fucus gardneri occurs from the Bering Sea and Aleutian Islands, Alaska to Santa Barbara, California.

Intertidal Height

Lowest intertidal height:

0 meters OR -2 feet

Highest intertidal height:

0 meters OR 1 feet

Intertidal height notes:

Fucus gardneri occurs in the mid to low intertidal.

Subtidal Depth Range

Minimum depth:

0 meters OR 0 feet

Maximum depth:

0 meters OR 0 feet

Subtidal depth notes:

Fucus gardneri does not occur in the subtidal.


bay (rocky shore), exposed rocky shore, protected rocky shore

Habitat notes:

Fucus gardneri grows on rocks and mussels, in exposed to sheltered habitats, in the mid to low intertidal.


Relative abundance:

Fucus gardneri is abundant.

Species Description

General description:

Fucus gardneri is a perennial brown alga that is often the dominant intertidal algae forming a dense band in the mid to low intertidal. It forms a short canopy that protects numerous other algae and inverts from wave action and desiccation during low tide. It also provides bases of attachment for sessile animals. Because it has wide salinity tolerances, it thrives on the outer coast, in inland protected waters, and even at stream mouths where it can be inundated with freshwater during changing tides.

Distinctive features:

Each individual Fucus gardneri has a discoid holdfast that supports a flattened, dichotomously branched thallus with a distinct midrib. At each fork of the midrib, both branches are of equal size. The blades are flattened about 15 mm wide. At maturity, the blades develop swollen tips called receptacles that contain air and mucilage. A cross section of a receptacle reveals multiple chambers called conceptacles where gametes are formed.


Individual Fucus gardneri are up to 50 cm long. Those at protected sites are usually larger than those at exposed sites.

Natural History

General natural history:

Fucus gardneri has a legendary ability to withstand desiccation and freezing during low tide. This suggests that individuals higher on shore may have thicker cell walls and higher water content. During times of low tides when Fucus gardneri partially dries out, it remarkably has the highest photosynthetic rates. However, individuals can become overstressed by desiccation and will develop softened areas and reddish spots. If extreme dehydration occurs, biochemical pathways will be disrupted and cell membranes may burst, leading to death. Fucus gardneri is thought to live two to three years at exposed sites, and up to four or five years on protected shores.

Young blades grow through terminal meristems, each controlled by the activity of a special apical cell, when this cell divides longitudinally, the blade forks. Heavy grazing by predators can lower growth rates significantly. In addition, studies have shown that only individuals with little damage from grazing are able to reproduce.

Fucus gardneri deters predators from grazing by means of natural chemicals called polyphenols that bind to proteins. These proteins make the algae indigestible because the polyphenols bind to and inactivate the digestive enzymes of the grazer. Polyphenol production is highest at the time of year when grazing is the highest and thus more grazing triggers more chemicals and should further deter grazing.


Fucus gardneri\\\\\\\'s predators include Periwinkle snails, Littorinaspp., Pacific Falselimpet,Siphonaria thersites, the Rockweed Isopod,Idotea wosnesenskii. Humans can eat it as well and in Alaksa it is harvested in the herring roe-on-seaweed fishery.


Fucus gardneri nourishes itself through photosynthesis, converting the energy of light to the energy of carbohydrate molecules.

Feeding behavior

Filter feeder, Photosynthetic