Invasive Alien Species Awareness Month in Hawaiʻi

Did you know that February was Invasive Alien Species Awareness Month in Hawaiʻi? Nowhere is invasive species more problematic than in the Maunalua Bay region, both on land and in the water.

In the water, invasive alien algae, or IAA, are one of the greatest threats to Maunalua Bay’s coral reef and nearshore marine ecosystem. These invasive, non-native marine algae species flourish off of an environment created by sediment and runoff from the land and low levels of herbivorous species in the water. As IAA spreads, it grows over and smothers coral reefs and outcompetes native algal communities, killing extensive areas of native habitat.

Three species of invasive algae are particularly devastating Maunalua Bay: Leather Mudweed (Avrainvillea amadelpha), Gorilla Ogo (Gracilaria salicornia), and Prickly seaweed (Acanthophora spicifera).

Leather mudweed is fan-shaped with spongy, densely clustered blades attached to a thick stalk, and is green to gray-green in color. It was once thought to prefer calm, shallow, sandy bottoms but is now found on diverse habitats, including rock and coral rubble, to depths of 80 m. It is considered the most detrimental IAA to the bay due to its ability to trap land-based sediment, ridding the coastal environment of oxygen and causing uninhabitable conditions for many native marine species, therefore degrading many coastal resources. It is not known exactly how Leather mudweed arrived in Hawai’i but it was first reported on O’ahu in the 1980’s.

Gorilla ogo has solid brittle branches that are cylindrical in shape. Gorilla ogo grows quickly, forming large, thick mats over the reef. One of the main concerns for Gorilla ogo is its rapid reproductive rate due to fragmentation. This means that the algae breaks off, drifts to another location, and can grow. It can also be spread by people moving pieces unknowingly. On O’ahu, Gorilla ogo was intentionally introduced on Oahu and Molokai in the 1970’s for experimental aquaculture for the agar industry.

Prickly seaweed grows in upright clumps of spiny branches, attached to hard substrate. This species can be pale yellow, brown, dark green, or reddish in color. Similarly to the Gorilla ogo, Prickly seaweed has a high growth and reproduces asexually through fragmentation, leading to widespread distribution. Prickly seaweed was unintentionally introduced through hull fouling in the 1950s.

If you are interested in learning more about native and invasive algae in Maunalua Bay, check out our field ID guide!