Division of Aquatic Resources

By Trevor Johannsen, Fishery Technician IV

The Hawaiʻi Division of Aquatic Resources (DAR) Aquatic Invasive Species (AIS) Team manages and prevents AIS in Hawaiʻi. One important responsibility of the AIS Team is to rapidly respond to non-native species introductions. When a species is first introduced, there is a short window of time in which it can be completely eradicated. Once an introduced species becomes established and widespread, eradication is often nearly impossible. Introduced species may be considered invasive when populations expand to the point of causing harm to native ecosystems, human well-being, or the economy and it is difficult to predict which introduced species have the potential to become invasive and which do not. Because of this, it is critical to treat all newly introduced species as a priority and to rapidly respond with an investigation and removal if possible.

In the past few months, the AIS Team has responded to several reports of newly introduced species and possible vectors of AIS spread. For each of these rapid response events, public support was crucial in reporting initial observations. The Division of Aquatic Resources encourages the public to report possible new AIS introductions to [email protected]. Please include photos and GPS coordinates when possible. DAR also encourages the public to use the crowdsourcing website www.inaturalist.org to track observations. With millions of residents and tourists enjoying reefs and oceans in Hawaiʻi every year, the potential for discovering an early outbreak of AIS can be increased. With continued public support, we can detect and respond to reports earlier and have a better chance of eradicating introduced species in Hawaiʻi.  

Manatee Mudflower
On July 6, 2023, the AIS Team received a report of a new aquatic plant introduction. The report was filed by Kevin Faccenda, a graduate student in the University of Hawaiʻi at Mānoa Botany Program. The species was confirmed as manatee mudflower (Micranthemum glomeratum), a freshwater aquatic plant native to Florida. It is unknown how this plant was introduced into the stream. However, manatee mudflower is a common freshwater plant in the aquarium trade, so it is probable that this introduction resulted from an aquarium dump.  Aquarium release is a common vector for the introduction of new species to Hawaiʻi. The AIS Team performed an initial investigation on July 26, 2023, and a more thorough survey downstream on September 5, 2023. During the surveys, the AIS Team discovered that manatee mudflower has spread from the initial point of observation to include several small patches about 200m downstream. Charles Chimera conducted a Weed Risk Assessment of M. glomeratum and concluded that this species poses a high risk of invasion because it can spread both vegetatively and by seed. Going forward, the AIS Team will be conducting delimiting surveys to determine the extent of the spread of manatee mudflower.

Manatee mudflower growing on a rock in Nuʻuanu Stream

Marine Debris
On September 27, 2023, The AIS Team responded to a report of marine debris that washed ashore near Kualoa Ranch on Oʻahu. The debris was identified as the refrigeration component of a shipping container that had undergone heavy biofouling the gradual accumulation and growth of aquatic organisms on the undersides of vessels or other floating objects. Most of the unattached organisms caught on the debris were common native algae or invasive algae already found in Hawaiʻi. The AIS Team collected samples of any suspected non-native or unknown organisms to give to Holly Bolick at the Bishop Museum for analysis. However, no immediate concerns were visually identified. The Hawaiʻi Division of Boating and Ocean Recreation removed the debris from the shoreline on the same day of the initial response. Floating marine debris is another common vector for introducing new species to the islands. It would have been a major concern if the AIS Team had found any unreported species.

Marine debris washed ashore near Kualoa Ranch

Caulerpa parvifolia
A newly introduced species of algae was recently discovered on Kauaʻi. In 2020, DAR received reports of unknown algae washing up on Kalapaki Beach and covering parts of the reef in Nawiliwili Bay. Genetic analysis determined the species to be Caulerpa parvifolia, another common species in the aquarium trade. Unfortunately, it was already infeasible to attempt any eradication at the time of discovery because the algae had become firmly established and widespread across the Bay. Follow-up surveys in the summer of 2021 showed a substantial thinning of the algae. However, additional surveys in the winter of 2022 found a resurgence with large mats in the Bay. In August 2023, the AIS Team assisted the DAR Kauai Team in surveying the easternmost part of Nawiliwili Bay which had not been previously surveyed. Caulerpa parvifolia was found to be present in low concentrations. To date, C. parvifolia has not been found outside of Nawiliwili Bay.

Caulerpa parvifolia growing in Nawiliwili Bay, Kauaʻi, in 2022