Christmas Tree Hydroid

Christmas Tree Hydroid (Pennaria disticha)

christmas tree hydroid

Photo courtesy of DAR

Description:

  • Branching colonial organism with a dark exoskeleton that surround a group of stems and branches (Hawaii Biological Survey, 2001)
  • Branches appear muddy brown and polyps are white with a reddish tint (Hawaii Biological Survey, 2001)

Habitat:

  • Attaches to hard substrates with some water movement (Eldredge & Smith, 2001)
  • Commonly found in harbors and protected reefs (Eldredge & Smith, 2001)

Impacts & Concern:

  • Ecological impact unstudied, likely competes with other native invertebrates and fouling organisms (Hawaii Biological Survey, 2001)
  • Stings cause irritation to humans (Eldredge & Smith, 2001)

Introduction:

  • Unintentionally introduced by fouling on hull of ship (Hawaii Biological Survey, 2001)
  • First reported in Pearl Harbor and Kāne‘ohe Bay in 1928 (Hawaii Biological Survey, 2001)

Distribution in Hawaii: (Coles et al., 2006)

  • Kauai: Present
  • O‘ahu: Kāne‘ohe, Pearl Harbor
  • Molokai: Present
  • Lanai: Present
  • Maui: Present
  • Big Island: Present

References:

  • Eldredge, L. G., & Smith, C. M. (2001). A guidebook of introduced marine species in Hawaii. Honolulu: Bishop Museum and the Univ. of Hawai’i.
  • Hawaii Biological Survey. (2001). Pennaria disticha. Introduced marine species of Hawaii Guidebook. https://www2.bishopmuseum.org/HBS/invertguide/species/pennaria_disticha.htm
  • Coles, S., Kandel, F., Reath, P., Longenecker, K., & Eldredge, L. (2006). Rapid assessment of nonindigenous marine species on coral reefs in the Main Hawaiian Islands. Pacific Science, 60(4), 483-507. https://doi.org/10.1353/psc.2006.0026