Invasive algae species recently detected along Kauaʻi’s south shore

The DLNR Division of Aquatic Resources is alerting the community to the presence of an invasive algae species recently detected along Kauaʻi’s south shore. Avrainvillea erecta was newly recorded on Kauaʻi in 2025. While the species has previously been documented elsewhere in Hawaiʻi, its confirmed presence along Kauaʻi’s south coast raises concern about its potential to spread and impact native marine ecosystems. 

Avrainvillea erecta is a large green algae that inhabits the sandy seafloor at depths of approximately 60 feet with observations on Kauaʻi ranging down to 120 feet and likely deeper. It is characterized by a distinctive single, fan-like blade that extends upward from a long stalk anchored several inches into the sand. In dense patches, A. erecta can form thick meadows that trap sediment, alter sandy habitats and potentially outcompete native species. Because it grows in deeper sandy areas, it may go unnoticed by many ocean users. 

In October 2025, DAR’s Aquatic Invasive Species team conducted surveys at known and suspected locations and confirmed A. erecta at Kaumakani, Lāwai Kai to Spouting Horn, and offshore of Kōloa Landing to Kiahuna Beach, Poʻipū. Survey results documented patch densities ranging from sparse to dense with some areas exceeding 80 percent cover. At this time, it is unclear whether these patches are connected or represent separate introductions. 

Requesting Help of Boaters and Fishers

One of the primary concerns with A. erecta is its ability to spread through anchoring activity. Anchors and anchor lines can snag blades or fragments of the algae, and even a small dried piece left on an anchor may be enough to introduce the species to a new location. Circular patch patterns observed at Kaumakani suggest that anchoring may already be contributing to its distribution. 

DAR is asking ocean users, especially boaters and fishers, to help prevent further spread by avoiding anchoring in areas where A. erecta is known to occur, particularly in deeper sandy habitats. If anchoring is unavoidable, anchors and anchor lines should be thoroughly cleaned and inspected after use and sanitized with spray alcohol or a diluted bleach solution before moving to another site. Be careful not to rinse any algae material on anchors or chains back into the ocean. One simple method is to place the anchor and chain into a 5-gallon bucket or similar container to collect any water and algae material while cleaning. The collected rinse water or cleaning solution should be disposed of on land and not poured back into the ocean or harbor.

Please report suspected sightings to DAR at dar.ais@hawaii.gov and include information about location and depth. Photos are strongly encouraged to confirm species identification.  

Early detection of new locations is important for limiting the spread of Avrainvillea erecta. While some areas along Kauaʻi’s south shore now contain established patches, reporting new sightings in other locations may allow DAR to respond quickly and remove small, localized patches before they become widespread. Taking action now can help suppress this invasive algae and protect Kauaʻi’s nearshore marine ecosystems.