Spiny Prickly Seaweed

Spiny Seaweed, aka Prickly Seaweed
(Acanthophora spicifera)



  • Seaweed that grows in upright clumps of spiny branches, 1-2 mm in diameter.
  • Can be pale yellow, brownish, dark green or reddish (often dark green in intertidal areas and high wave motion areas)
  • Grows on the reef in intertidal, lagoon and reef flat habitats, or can be free floating
  • Accidental introduction to Hawaii from Guam in 1950. Introduced by hull fouling on the fuel barge “Yon 146”. The first fragments of this species were discovered in Pearl Harbor in 1952. It can now be found on all main Hawaiian Islands.


  • Outcompetes native seaweeds for space on the reef.
  • Readily reproduces and spreads by fragmentation (floating pieces of seaweed) and spores, and continues to spread attached to the hulls of boats.
  • Fouls the hulls of boats interisland transport, making them less fuel-efficient.

In Hawaii:

All main Islands: It is the most abundant seaweed species on shallow reefs and the most widespread alien seaweed in Hawaii. Widescale control or eradication is not currently feasible.

For more information, see: