A traditional mauka-to-makai approach to restoring the scarred landscape of Kahoolawe is reducing erosion and sedimentation in nearshore waters, clearing the way for new coral growth and a healthier marine environment.

Two centuries of grazing by livestock and feral animals and 50 years of military bombing stripped the 45-square-mile island of much of its vegetation, leaving it vulnerable to severe erosion. An estimated 1.9 million tons of topsoil have been washing into the ocean annually.

But a new monitoring program by the Kahoolawe Island Reserve Commission in collaboration with the U.S. Geological Survey, with funding from the state Department of Health and U.S. Environmental Protection Agency, shows clear evidence that erosion has decreased 75 percent in certain areas.

"I remember flying over the island and seeing a perpetual red ring. Now that's definitely not as apparent," said Dean Tokishi, an ocean resources specialist for the commission, which manages activities on the island.

Since September 2003, staff and volunteers have planted 150,000 native grasses, shrubs and trees as part of a massive restoration plan. Short-term results from the monitoring program show that replanted sites retained 7.6 tons of sediment per acre, while unrestored areas lost 5.6 tons of soil per acre, according to a 2009 report on the watershed restoration project.

With the reduction in soil runoff, removal of feral goats, and the action of waves and currents pushing sediment offshore over time, newly re-exposed underwater surfaces are being colonized by reef corals.

Despite the years of bombing, the extensive reef system around the island is relatively intact and is believed to be the best example of a natural marine ecosystem in the main Hawaiian Islands. A 2002 study by researchers Alan Friedlander and Edward DeMartini found that Kahoolawe has the highest biomass of fish in the main islands at 1.28 tons per hectacre (2.47 acres) — double the biomass of fish off Oahu.

Kahoolawe also has the highest representation of apex predators, such as sharks and jacks, among its total fish population at 12 percent. Next highest is Maui, at only 2.4 percent.

An abundant population of apex predators is an important indicator of a marine ecosystem's well-being, Tokishi said.

"In order for the apex predators to survive, there's got to be a strong and healthy base. It means everything is in place," he said.

Control of access to the island was granted to the state only six years ago following a $400 million federal ordnance cleanup project, so marine scientists have had only a short while to conduct research. Even without baseline data or long-term studies, Tokishi said, there are signs — such as regular visits by endangered monk seals and a wide diversity and abundance of fish — that the marine environment is faring well.

And because fishing is banned in Kahoolawe's waters, the area has become a sanctuary where fish can reach optimal breeding sizes.

"The reserve is definitely having a positive effect on neighboring waters, everything from spillover with bottomfish to providing a seed source for the rest of the chain. The reserve acts as a nursery," Tokishi said.

Protected from fishing pressure, parrotfish and other limu-grazing species are keeping harmful invasive algae from becoming established on Kahoolawe's reefs, a persistent problem in other nearshore areas of the state.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.