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Have you seen invasive seaweeds?
Hawaii Early Detection Network Priority Pest for the islands of Kauai, Maui, Lanai, Molokai, and the Big Island Hawaii


Gorilla ogo
Gorilla Ogo is only known to be on Oahu and Hawaii
agar agar seaweed picture
Eucheuma denticulatum is only found in a few places on Oahu
Rubber vine
Kappaphycus species are the fastest growing tropical algae, doubling in biomass in 15-30 days

Aquatic invasive seaweeds are one of the factors contributing to an overall decline of Hawaii's coral reefs. To date, 12 species have been introduced into Hawaiian waters. They reproduce quickly and outcompete native species for space and food. On Maui, keep an eye out for gorilla ogo (Gracilaria salicornia) external link, agar-agar (Eucheuma denticulatum) external link, and Kappaphycus species external link. These seaweeds have been found on other islands, but not in large quantities on Maui. Gorilla ogo is a cylindrical to flattened shaped seaweed that is red to orange in color. It grows to 4" long and 1/10" around. The Kappaphycus species are tough, fleshy, firm seaweeds that grow to 6' tall and are yellow to shiny green depending on light conditions. Agar-agar is similar to the Kappaphycus species, but with spiny branches.
Impacts: Invasive seaweeds can overgrow shallow reefs, indicating an imbalance between factors which promote algal growth, such as nutrient availablility, and those which control algal abundance, such as grazers like sea turtles and herbivorous reef fish.
Dispersal Mechanism: Many non-native seaweeds can reproduce from small broken pieces. These pieces are tranported via contaminated snorkel/dive gear, contaminated fishing gear, the ballast water of ships, aquarium dumping, by grazing fish and turtles, water currents, and the deliberate introductions of commercial species.

More information to help you identify invasive seaweeds:
University of Hawaii- Invasive Marine Algae of Hawaii external link
Alien and Invasive Algae in Hawaii external link
Reef watcher's guide to alien and native marine algae external link


Invasive Seaweed look-alikes:


Native limu:
There are around 500 species of macroalgae in Hawaii. Many of the native seaweeds, or limu, are closely related to the non-native invasive species. Look-out for: limu manauea (Gracilaria coronopifolia) external link which can superficially resemble gorilla ogo (Gracilaria salicornia). Limu manauea is skinnier and often lighter in color than gorilla ogo.

limu manauea

Limu manauea (Gracilaria coronopifolia)

Last Updated: Monday January 30 2012. If you have any questions about the Hawaii Early Detection Network contact reportapest-maui@lists.hawaii.edu.
Funding and support for this project was made possible by the Hawai'i Invasive Species Council, the USDA Forest Service State and Private Forestry assistance, and University of Hawai'i-Pacific Cooperative Studies Unit.