Bladder Wrack

Rockweed – Bladder Wrack

Fucus sp.  (3 species and several subspecies)
(F. spirillis, F. vesiculosus,  F. distichus, F distichus ssp. edentatus,

 bladder wrack

Phylum: Phaeophyta (brown algae)
Family: Fucaceae

Bladder Wrack is one of the most dominant types of perennial rockweed in the intertidal zone.  Its olive green to dark brown blades can be seen growing amongst barnacle covered rocks and piers.  Different species can be distinguished by looking for air bladders, which help them float, and warty receptacles and the ends of the blade that contain gametes1,2.  You can distinguish Fucus sp. from Asophyllum nodosum because the blades are flat with a prominent midrib2 and always divide into two like the letter ‘Y’.  All Fucus sp. Have receptacles and the ends, but air bladder/vesicle development depends on how calm the water is1.  The information below illustrates the differences between Fucus species.

Air Bladders (Vesicles): usually paired (if present)1,2
Receptacles (at the tips): swollen, warty ovals2
Range: Arctic to North Carolina2
Other: F. vesiculosus may reach 60cm (2’) in length1 and is the most common of all Fucus species.  Some variants may lack air bladders making it hard to tell the difference between this species from F. spirillis.

 F. spirillisFucus spirillis
Air Bladders (Vesicles): not paired1
Receptacles (at the tips): swollen with a distinct ridge around the circumference1
Range: Newfoundland to Long Island Sound2
Other: F. spirillis  is smaller than F. Vesiculosus1 and can be found closer to shore2.  It also exhibits a twisted growth pattern1.


F. distichus ssp. edentatus1,2
or  F. edentatus2
Air Bladders (Vesicles): always absent1,2
Receptacles (at the tips): shaped like flat finger2
Range: Newfoundland to Long Island Sound2

F. distichus ssp filiformis  or F. filiformis2
Air Bladders (Vesicles): always absent2
Receptacles (at the tips): shaped like fingers, but not flattened2
Range: Subarctic to Northern Massachusetts2
Other: F. filiformis has narrow blades, and is hard to distinguish2.

F. distichus ssp evanescens2 or F. evanescens2
Air Bladders (Vesicles): always absent2
Receptacles (at the tips): flat, small2
Range: Arctic to Long Island Sound2
Other: F. evanescens2 is found in the early subtidal zone2

F. serratus2
Air Bladders (Vesicles): always absent2
Range: Nova Scotia to Gaspé
Other:  F. serratus2 is hard to distinguish. Look for serrated margins on the blades.2

1. Watling, L., Fegley, J., Moring, J., White, S., Sulzer, A. (2003) Life Between the Tides. Tilbury House Pub

2. Gosner, Keneth L. (1978), Peterson Field Guides: Atlantic Seashore – A field guide to sponges, jellyfish, sea urchins, and more




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