Hawai'i's Environment
Overgrowth of seaweed studied
By Jan TenBruggencate
Advertiser Columnist
Four alien seaweeds have overgrown acres of Kane'ohe Bay.
A native species of limu has joined them, having become an aggressive spreader over of the coral reef.
"The spread of these alien algae and the effects that have resulted are quite alarming. In some places such as Kane'ohe Bay, whole patch reefs are being overgrown with these invasive species resulting in a major decline in coral cover," said Bill Devick, head of the state Division of Aquatic Resources.
The reasons for the aggressive growth of the limu are many. Some aliens have been introduced without the natural predators and diseases that controlled them in their home range.
But, as the spread of the native limu — Dictyosphaeria cavernosa or green bubble algae — indicates, there are other factors, too. The limu are also assisted by excessive nutrients — essentially, fertilizer — in coastal waters. Limu, after all, are plants, and fertilizer makes them grow faster.
And the fast growth is also assisted by something you might not have considered—overfishing.
Many limu are kept under control by plant-eating fish. When too many of those fish are removed by anglers, netters and spear fishers, it can allow the seaweeds to grow out of control.
But which of these issues is the most important, and which can most readily be changed to reduce the damage foreign limu are causing to our reefs?
"It is important to study the dynamics of these extensive blooms so as to offer advice to land managers on how to reduce the scale of these problems," says University of Hawai'i researcher Jennifer Smith.
Smith is studying the reasons for and the impacts of algae overgrowing coral reefs, along with fellow algae and coral experts Isabella Abbott, Cindy Hunter, Celia Smith and others.
"These algae are growing over portions of the reef, and may be damaging the underlying coral organisms," Smith said.
The Hawai'i Coral Reef Initiative will issue a grant early next year to determine whether it is possible to eradicate the alien seaweeds at Kane'ohe.
Among the remaining questions will be how to limit the conditions that let these limu grow out of control, and how to prevent new ones from constantly arriving.
Smith will give a free public talk on the threats of alien limu to Hawaiian coral reefs at at noon Thursday in the Department of Land and Natural Resources conference room at 1151 Punchbowl St., Room 132, in Honolulu.
A great deal of information about alien algae is available at Smith's university Web site.
Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. You can call him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.
