Invasive Octocorals & Anemones: A Growing Threat to Hawaiʻi’s Reefs

By Kirsten Kagimoto, Chapter Deputy Director | Reading time: 5 minutes

Pulse octocoral, Unomia stolonifera. Photo: DLNR

While coconut rhinoceros beetles, little fire ants, hala scale and other invasive pests continue to threaten the well-being and resilience of our ʻāina, our kai is also under siege. Devastating invasive species are spreading across our coral reefs, further endangering our food systems, marine life, and climate resilience. 

In recent years, highly invasive octocorals and anemones have been found in Puʻuloa and Kāneʻohe Bay, outcompeting native corals, smothering reefs, and disrupting marine ecosystems. Their rapid spread threatens biodiversity, reef health, and the sustainability of fisheries and coastal ecosystems.

As we continue fighting to stop the spread of invasive pests on land, we must also demand urgent action to prevent the introduction and spread of invasive species in our oceans—and hold responsible parties accountable.

What Are Invasive Octocorals and Anemones?

Octocorals are a type of soft coral with flexible, branching structures composed of tiny polyps, each with eight tentacles. Unlike reef-building corals commonly found in Hawaiʻi, octocorals do not form calcium carbonate structures but can spread aggressively, outcompeting native species. There are no native octocorals in Hawaiʻi.

Majano anemone, Anemonia manjano. Photo: DLNR.

Two species of invasive octocorals have been found in Puʻuloa, pulse coral and Kenya green tree coral, both native to the Indo-Pacific. These soft corals are popular in the aquarium trade but are illegal to own in Hawaiʻi. The pulse coral is of particular concern—it has already spread across over 100 acres in Puʻuloa.

Another major concern is the majano anemone, an invasive species native to the Indian Ocean. This small, fast-spreading anemone is notorious for taking over reef environments and smothering native corals. It has been found in both Puʻuloa and Kāneʻohe Bay, with a particularly alarming infestation in Kāneʻohe Bay covering 950 square yards in just a few years. 

Majano anemones are popular among novice aquarium hobbyists due to their resilience but most aquarium collectors know to steer clear because they can even dominate tank environments.

How Did These Species Get Here?

Delayed Response to Octocoral Spread: The US Navy first detected invasive octocorals in Puʻuloa in late 2020, but did not notify state agencies for two to three years. The delay likely allowed the population to expand dramatically.

Because of its popularity as an aquarium species, it is believed that the species was released by an unauthorized aquarium dump near the Hickam Fishing Pier. 

Aquarium Frenzy: Majano anemones in Puʻuloa are also believed to have been introduced through illegal aquarium dumping. However, in Kāneʻohe Bay, their presence is likely a part of an intentional illegal coral planting, driven by profit-seekers hoping to cash in on the aquarium trade. 

The US aquarium industry, valued at $2.2 billion in 2023, is the world’s largest consumer of marine aquarium species. This growing industry has fueled illegal imports of harmful corals and invertebrates, the intentional outplanting of invasive corals on reefs to later harvest and sell, and the overcollection of key native species like lauʻipala, yellow tang, and kole, yellow-eyed tang. 

Without stronger biosecurity regulations and aquarium trade policies, the aquarium trade will continue to introduce devastating species into Hawaiʻi’s fragile ecosystems while profiting off of the take of critical species.

What’s At Stake

Both octocorals and majano anemones have no natural predators in Hawaiʻi and can reproduce through fragmentation—meaning that even a tiny broken piece can grow into a viable adult. 

Majano anemones pose an even greater challenge, as they can detach and relocate on their own. They are also hermaphroditic, meaning they can reproduce independently and release spores when threatened, rapidly increasing their numbers. Because of this easy reproduction and spread, these species are difficult to eradicate, especially as populations grow. 

The impacts of these species include:

• Smothering native corals, destroying reef fish habitats

• Disrupting entire marine ecosystems, leading to declines in fish stocks

• Reducing reef resilience, weakening natural protections against coastal erosion

• Damaging recreation and tourism, as pulse octocorals emit a strong rotting fish smell that can spread to fish in the area

What’s Being Done?

In early 2023, the US Navy cleared over 33,850 square feet of octocorals in Puʻuloa, but the species quickly regrew. This failure underscored the need for a long-term, large-scale eradication effort. 

The Navy has since tested different methods to kill the octocoral and now believes it has a successful way to eradicate it—smothering the coral with heavy tarps for over a week to kill them. Dependent on funding, the Navy is preparing to soon implement this strategy on a larger scale.

However, in addition to the sheer amount that needs to be eradicated, there are other factors that could hinder efforts, such as in Puʻuloa where there is a lot of vessel traffic in the harbor that could contribute to the coral’s spread over time. 

The Hawaiʻi Invasive Octocorals Working Group, which includes state and federal agencies, academic institutions, and conservation organizations, is coordinating research, removal, and prevention efforts.

State conservation officials have also developed a plan to eradicate the majano anemone before it spreads beyond Kāneʻohe Bay. The Hawaiʻi State Legislature is moving forward with a $200,000 funding proposal, with eradication efforts potentially starting this summer.

What You Can Do

Don’t Let It Loose: One of the main ways invasive marine species spread is through illegal aquarium dumping. If you have a home aquarium or know someone who does, never release any animals or plants from your tank into Hawaiʻi’s waters. You can also turn over illegal animals to Hawaiʻi’s amnesty program.

If you spot a marine species you suspect to be invasive, call the Division of Aquatic Resources at 808-587-0100 or email DAR.AIS@hawaii.gov. For terrestrial invasive species, report them to 808-643-PEST or at 643pest.org. 

Support Majano Anemone Funding: Legislation is moving forward this year to fund the state’s efforts to remove the majano anemone before it spreads further. Track and support this legislation here. 

Advocate For Stronger Biosecurity: Hawaiʻi is battling dozens of invasive species that threaten our environment and resilience—from mauka to makai. Every day that passes without strong action allows infestations to spread unchecked. We need bold policies and enforcement to protect Hawaiʻi’s biodiversity. Learn more about our invasive species work here and sign up for invasive species email alerts here.

Act Now or Pay Later

Hawaiʻi has seen success when new invasive species are tackled immediately and aggressively—like fireweed on Kauaʻi and axis deer on Hawaiʻi Island—but failures when response efforts are too slow or inadequate—such as the delayed action against coconut rhinoceros beetles and little fire ants by the Department of Agriculture.

The lesson is clear: If we do not act now, invasive octocorals and anemones will follow the same disastrous path. We must demand action—before it’s too late.