Rockweed    Fucus spiralis



This species of seaweed and it's close sibling, Fucus gardneri, (both called rockweed) are very common in the mid to high tide zone throughout Puget Sound.  They are members of the brown seaweed group called Phaeophyta to which the kelp also belong.  The inflated bulbs at the end of the blades along with a midrib in the blade are major distinguishing characteristics of rockweed.  The bulbs are filled with air and mucilage that allows the blades to float exposing them to sunlight and allowing water to move through the branches.  


Gardneri is very similar to spiralis but lacks the thin flange ringing the inflated bulbs as seen in this photograph and has a more prominent midrib.  Spiralis, which occurs higher in the intertidal zone than does gardneri, ranges from the Aleutian Islands south to Washington. Gardneri occurs throughout the same area but continues into southern California as well.


The bumps on the bulbs are reproductive structures called pits or conceptacles.  Special cells within the pits produce eggs and sperm which are released into the water column and fuse producing a baby plant.  The new plant then grows directly into an adult. Reproduction occurs through the year. Other seaweeds have a more complicated reproduction cycle where one form produces eggs and sperm while another form produces spores.


Rockweed was once used by humans for cattle fodder and mulch but is not used today. However it serves a significant function as habitat for a variety of animals at all stages of the tide.  Periwinkle snails and small crustaceans hide among the branches when the tide recedes while small fish move into the branches to feed at high tide.