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) , agar-agar (Eucheuma denticulatum) , and Kappaphycus species . 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.

Characteristics:

Invasive seaweeds look-alikes:

Native limu:
There are around 300 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) which can superficially resemble gorilla ogo (Gracilaria salicornia). Limu manauea is skinnier and often lighter in color than gorilla ogo.