Hook Weed

Hook Weed (Hypnea musciformis)

Hypnea musciformis

Hypnea musciformis


  • Masses of intertwined branches, with the ends of the projections forming hooks (EOR, 2015)
  • Usually a red color but can be yellow or brown in some environmental conditions (UH Botany Dept., 2001)
  • Can spread and reproduce through fragmentation, waves break off hooks which drift and attach to other locations (HISC, 2017)


  • Often found attached to rocks and reef algae in intertidal pools and beaches (EOR, 2015)
  • Can be found free-floating in bloom stage (UH Botany Dept., 2001)

Impacts & Concern:

  • Rapid growth rate and easy fragmentation (EOR, 2015)
  • Ability to grow on other drifting seaweeds (CABI, 2019)
  • Mats of seaweed wash up on beaches resulting in decreased beach use and property values (HISC, 2017)
  • Competes with and overpowers local native algae and corals (CABI, 2019)


  • Illegally introduced to Kāne‘ohe Bay from Florida in 1974 (UH Botany Dept., 2001)
  • Intended for commercial aquaculture use (UH Botany Dept., 2001)

Distribution in Hawaii: (HISC, 2017)

  • Kauai: Found at Prince Kuhio Beach and Salt Pond Beach
  • O‘ahu: Large amounts from Kahala to Makaha
  • Molokai: Found in some areas including Kaunakakai and Kupepe
  • Lanai: Not documented
  • Maui: Large amounts on windward and leeward reefs
  • Big Island: Not documented


  • Eyes of the Reef (EOR). (2015). Hookweed (hypnea musciformis). Eyes of the Reef Hawaiʻi. https://eorhawaii.org/education/marine-invasive-species/hypnea-musciformis/
  • CABI Invasive Species Compendium. (2019). Hypnea Musciformis. [Data sheet]. https://www.cabi.org/isc/datasheet/107763
  • UH Botany Department. (2001). Hypnea Musciformis. Marine Algae of Hawaiʻi. https://www.hawaii.edu/reefalgae/invasive_algae/rhodo/hypnea_musciformis.htm#
  • Hawaii Invasive Species Council (HISC). (2017). Hookweed (Hypnea musciformis). https://dlnr.hawaii.gov/hisc/info/invasive-species-profiles/hookweed/