Rubber Threads (Nemalion helminthoides)

Looking somewhat like dark brown over-cooked spaghetti draped over the barnacle encrusted rock of the high intertidal on Magic Island, the aptly named rubber threads (Nemalion helminthoides) were new to me. As far as I can tell at this point (still early in my learning about marine algae), there is not really anything else they would be mistaken for. Described in the Seaweeds of Alaska as a summer annual, they only mention the possibility of mistaking these for marine worms. I imagine that’s easier to do when the strands are young, as to my eyes, what I observed would not be mistaken for a worm.


  • What triggers these to start growing in the summer? (photoperiod? water temperature?)
  • What is happening with them during the non-growing season?
  • How do they get started up so high in the intertidal, and what keeps them from growing lower?

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