Early Detection Key to Keeping Kaua‘i’s Streams Healthy

By Ruby Pap

Salvinia molesta collected from Kilauea. Photo courtesy of Kelsey Brock

If you see Salvinia molesta (Salvinia) in any of our streams please report it immediately to the Kaua‘i Invasive Species Committee (KISC) at 821-1490. In doing so, you will help prevent this noxious weed from taking over the ecosystem.

Commonly known as Giant Salvinia, Salvinia is a free-floating aquatic fern consisting of horizontal stems that float just below the surface. It contains three leaves at each node, which are covered with white, bristly hairs resembling tiny egg beaters.

It can spread easily via human activity such as crab traps, fishing gear or kayaks, so be sure to inspect and clean your gear away from streams and waterways. Recent sightings on Kaua‘i have left scientists, community members and resource managers concerned about its spread.

Salvinia is native to South America but invasive elsewhere, including Hawai‘i and the continental U.S. It was introduced through the horticulture and aquarium trade. Federal law bans the sale, transport and release of this plant and it is listed on the Federal Noxious Weed List.

Salvinia molesta close up. Photo courtesy of Mugs Kaneholani

Salvinia grows rapidly in freshwater (streams, wetlands, lakes, ponds, reservoirs) and forms dense floating mats that reduce water flow, cut off light to other aquatic plants, and reduce oxygen. This causes dangerous conditions for fish and other aquatic organisms such as the native o‘opu (stream goby) and ōpae (shrimp). Salvinia can also clog waterways and culverts posing flooding and navigational issues. The weed caused a major stir on O‘ahu in 2003, when it completely took over Lake Warren, resulting in costly eradication efforts.

Bob Warren of Kīlauea remembers first spotting Salvinia on Kaua‘i’s Kīlauea Stream about 10 years ago. It was kept relatively under control by KISC, but in recent years it has taken off. Warren got together with Kīlauea neighbors to do some manual removal but they barely made a dent, causing great concern within the community.

“I started contacting everybody, trying to get somebody interested,” Warren said.

That’s when he found Brian Neilson, the Aquatic Invasive Species Coordinator for the state Department of Land and Natural Resources, Department of Aquatic Resources (DAR). DAR personnel is now planning to work with the Kīlauea community, KISC, Hawaiian Islands Land Trust and others on a management plan for Salvinia in Kīlauea Stream. Manual removal efforts are planned this year using the “super sucker,” a pump that was used to remove invasive algae from reefs on O‘ahu. Warren and neighbors pooled their resources and were able to provide funding for DAR to ship the pumps over to Kaua‘i later this year.

Salvinia molesta in Kilauea Stream May 17. Photo courtesy of Brian Neilson

In the meantime, DAR is out “knocking on doors,” seeking funding to expand their early detection efforts for Salvinia on Kaua‘i, which has been detected thus far in Kīlauea, Kapa‘a, and Pu‘ukumu streams. KISC’s recent discovery on Pu‘ukumu Stream is significant because Salvinia was previously thought to occupy only stagnant, low-flow waters (e.g. near stream mouths). In this case it was found in a smaller, higher energy mauka area of the stream.

“At first I thought, ‘that doesn’t make sense.’ I expected to see a different aquatic weed, but there it was,” said Kelsey Brock, Early Detection Botanist for KISC.

This tells her Kaua‘i may have additional smaller feeder populations further upstream, potentially prolonging the battle.

This is why early detection is so important. Neilson and colleagues recently piloted a new monitoring technology called, EDNA, that could make the process easier. It involves scanning stream water samples for the specific Salvinia DNA marker sequence to determine presence or absence of the plant. Neilson is hoping to expand the sampling to every stream mouth on Kaua‘i to get a much better idea island-level impacts, but this will require additional funding.

Kaua‘i needs everyone’s help to detect, report, and prevent Salvinia’s spread. Contact KISC at 821-1490 to report sightings.

• Ruby Pap is a Coastal Land Use Extension Agent at University of Hawai‘i Sea Grant College Program. She can be reached at rpap@hawaii.edu.