Weed threatens several ponds
| • | Where Salvinia molesta can be found |
By Eloise Aguiar
Advertiser Windward O'ahu Writer
KAILUA — An aggressive plant considered one of the world's most noxious weeds has been identified in at least three more locations statewide including Kawainui Marsh, and Windward residents want intervention to prevent the invasive species from overwhelming the marsh as it has Lake Wilson in Wahiawa.
Salvinia molesta, a popular bright-green aquarium plant, has been identified in drainage ditches and canals on the perimeter of the marsh. The weed also was recently discovered in a stream below the Ho'omaluhia Botanical Garden in Kane'ohe and in the Waiakea pond in Hilo.
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| Eric Guinther gives tours of Kawainui Marsh. He is standing near a tributary on Kapa'a Quarry Road, which is overrun with Salvinia molesta, a plant that has covered the water. The same plant has overrun Wahiawa's Lake Wilson.
Deborah Booker • The Honolulu Advertiser |
The plant has been growing since 1999 in Ka'elepulu Pond in Enchanted Lake in Kailua and in an explosion of growth since late last year now covers about 90 percent of Lake Wilson, threatening a mass fish kill if it isn't stopped by summer.
Kawainui Marsh, covering about 800 acres, is a significant cultural resource containing dozens of historic sites. It also is seen as the centerpiece for a park with a walkway around the perimeter and new waterways for bird habitat.
The marsh is already overgrown with alien plants, including salvinia, and they will all someday overrun the wetland, said biologist Eric Guinther. He said salvinia, a fern, has been in the marsh for about a year but water hyacinths, other ferns such as water cabbage, azolla and a thick grassy mat have covered almost all of the marsh for decades.
Only about 10 acres of open water remains in the marsh, he said.
"I expect all of it will be gone in a couple of years at the rate that stuff spreads," Guinther said.
Salvinia molesta is known to double its coverage in a week under favorable conditions and can reproduce from the tiniest clipping. So during removal efforts if one small piece breaks off and is overlooked, it will grow a new plant.
Salvinia grows in slow-moving or quiet fresh water and dies in salty environments. It tends to overgrow and replace native plants, preventing light and oxygen from entering the water. When it decomposes on the bottom of a pond or stream, it consumes oxygen necessary for fish and other aquatic life.
Over time it drains the life from a body of water.
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| Snail eggs hang on a wooden stick in the Kawainui Marsh in Kailua. The marsh's eco system is fragile, and invasive plants such as Salvinia molesta are a challenge to keep out.
Deborah Booker • The Honolulu Advertiser |
"It chokes everything," said Kailua Neighborhood Board member Knud Lindgard.
Early, aggressive intervention appears to be the key to keeping the plant under control. That's what worked in Kailua's Ka'elepulu Pond in Enchanted Lake. A citizens group noticed the rapid growth of salvinia in the lake and removed the weed on their own in 1999. Since then neighbors have been vigilant and do periodic cleanings.
Guinther and others have begun clearing parts of Kawainui Marsh in an effort to fight the invasion there.
Officials are also trying to expand the fight to reclaim Lake Wilson. Hampered by a lack of money and resources, state workers have been fighting a losing battle to stop its spread, said Glenn Higashi of the state Department of Land and Natural Resources Division of Aquatic Resources. He said he has been working with only two technicians.
Last week, Sen. Robert Bunda, D-22nd (North Shore, Wahiawa), hosted a meeting of state, federal and city officials and private enterprises to develop an eradication plan. Over the weekend, five fishing clubs were joining the battle with help from the DLNR, attacking salvinia by hand.
The city lent a hand in December, providing a loader and dump trucks, and the Army Corps of Engineers has said it will help by providing experts later this month, Higashi said.
But those hoping to save Lake Wilson face a tight summer deadline when plant production and decay increase, sucking the oxygen out of the water and threatening a massive fish kill, Higashi said.
Lindgard says a salvinia weevil could solve Hawai'i's salvinia problem.
Texas and Louisiana experiments with the weevil have reported some success in reducing the growing mat over a one-year period, according to a Web site for the U.S. Geological Survey. The experiment is ongoing.
Lindgard said he's pushing for a controlled experiment in Hawai'i. Bringing in another alien bug is a concern, he said, but a test of the weevil with local plants would determine whether the bug could be harmful to the Islands' native plants.
"It's going to be a disaster" if salvinia is left unchecked, he said. "At least we should try something like this."
Athline Clark, with DLNR aquatic resources, said Hawai'i has not had good luck with bringing in one organism to control another. That option would have to be carefully studied, Clark said.
Kathy Bryant-Hunter, Kailua Neighborhood Board chairwoman, said she supports Lindgard's suggestions and is disappointed that nothing seems to be happening. As an interim step, people could remove the weed by hand, she said.
"I think we could rally volunteers to do that. It's just who's in charge? Tell us and we'll try to work with you."
Reach Eloise Aguiar at eaguiar@honoluluadvertiser.com or 234-5266.
