KILAUEA — Many hands have removed large amounts of the invasive aquatic plant salvinia from the Kilauea River over the past few years, but nature’s April flooding really swept it downstream.
In fact, coverage in the river went from about 20 percent, and 50 percent in a select few areas along the river, to 5 percent after the rains washed it into the ocean’s saline water, where it can’t survive.
But residents and officials are still concerned as the river isn’t completely clear of the plant and data from eDNA (environmental DNA) samples shows it has spread to other areas on Kauai.
“Positive samples were found in the Kapaa, Kilauea and Puukumu streams. A weak signal was also found in Waimea, but further follow-up is needed to determine whether salvinia is present in that stream,” said Tiffini Keanini, project manager for Kauai Invasive Species Committee, one of several entities helping to tackle the problem.
Positive samples mean there was salvinia DNA in the stream but does not necessarily mean salvinia is established in the stream.
The state Department of Land and Natural Resources Division of Aquatic Resources completed the islandwide survey for eDNA of salvinia in 2018 on all perennial streams on Kauai. The U.S. Fish and Wildlife Service and the state Department of Agriculture are also involved in salvinia response.
Pam and Bob Warren are Kilauea residents dedicated to helping eradicate the plant from Kilauea River and preventing the spread to the rest of the island.
They’ve teamed up with neighbors to host cleanups with kayaks and paddleboards, manually pulling the salvinia from the river and letting it die in the salt water at Kahili Beach, also known as Rock Quarries, before further disposal.
“It spreads like a lot of other invasive species. A kayaker will have some of it on their paddle or on the boat and then it spreads to other waterways with them,” Bob Warren said.
Driving the family’s little boat “River Baby” upstream, he and Pam pointed out the clumps of salvinia still clinging to the banks, interwoven between California grass and caught on sticks where the current slows.
“Salvinia likes the California grass,” Pam Warren said. “That makes it hard to get because the California grass has long roots that grow until they anchor to the bottom.”
The aggressive, leafy plant forms mats of thick vegetation that tangle in with the California grass and reduce the amount of sunlight and oxygen available underneath. That impacts the ecosystem of the entire river.
KISC describes the plant as having oblong floating leaves, half an inch to an inch and a half long, and experts say it was introduced to Kauai as a decorative aquatic plant that got out of control and now threatens bodies of water like rivers, reservoirs and taro fields.
In the Kilauea River, where it is believed salvinia started invading Kauai, nature took care of the bulk of the plant and the Warrens say now is the time to wipe out the rest.
“We can’t expect and don’t want heavy rain events like we’ve been having,” Bob Warren said. “So we should take care of it now.”
“The salvinia, it’s at a manageable level now,” Pam Warren added.
Currently, there are a few options that have been floated in brainstorming sessions between the Warrens, other community members and officials. Those methods of attack include a high concentration of salt water, using an herbicide to exterminate the plants, or introducing the salvinia weevil, known only to eat that specific plant.
Concerns about disruption of the river’s ecosystem are connected to all three of the remedies in conversation.
“The best course of action now, in the best interests of the streams, is to use this opportunity of low levels of salvinia to proceed with herbicide control to remove remaining small fragments and prevent regrowth,” Keanini said. “Coordinated planning and permitting for the control effort will involve the expertise of multiple agencies.”
All of that is being considered while individuals patrol the river and remove salvinia when they see it. Cleanups are ongoing.
And while the bulk of the salvinia is in the Kilauea River, officials and stakeholders say they’re concerned about the rest of the island.
“It’s highly invasive, and if we don’t get a handle on it, it could cover whole reservoirs,” Bob Warren said.
Jessica Else, environment reporter, can be reached at 245-0452 or firstname.lastname@example.org.