The reef along Moloka'i's south shore stands out for many reasons.

It is the longest fringing reef in U.S. waters and has more coral cover than any other around the main Hawaiian Islands. Nearly all the coral species known to be in Hawai'i are found there.

It also is a vital marine and cultural resource. Experts say South Moloka'i's reef flat -the wide, shallow section closest to shore — probably is the most productive in the main Islands for harvesting of reef fish and invertebrates.

But the roughly 30-miles-long reef stands out for more disturbing reasons as well.

As spectacular as it is, the marine ecosystem is under siege, mostly from fallout linked to human activities. Because the reef only has a thin layer of living corals, it is considered particularly fragile, susceptible to the same threats facing reefs worldwide.

Scientists already have discovered evidence of widespread damage, mainly on the reef flat, from tons of eroded sediment that have flowed into the ocean over the years. In some places, the degradation is severe.

And scientists, residents and environmentalists fear the damage will spread if more isn't done to address the pollution problem, overuse of reef resources and other threats.

"We really have not been good stewards of the land or the reef," said Moloka'i resident Bill Feeter, 79, who used to regularly windsurf off the south shore.

DATA SUPPORT CONCERNS

Data from several ongoing scientific studies underscore their concerns:

• Erosion along South Moloka'i's hillsides is well above what would be considered natural. At some of the steepest, most exposed spots, the erosion rates are roughly 100 times higher. Feral animals grazing on the slopes, fires that burned large patches of vegetation and lands cleared years ago for ranching or agriculture have been among the factors contributing to the long-time erosion problem.

• During a two-year period ending in 2006, more than 8,700 tons of sediment washed onto the reef flat from Kawela Stream, one of many outlets along the south shore. About 90 percent of that total was discharged in just nine days.

• Six sites off Moloka'i's south coast collectively had the largest decline in coral cover from 2000 to 2002 compared with the totals by island from monitoring spots off O'ahu, Maui, Kaua'i, the Big Island and Kaho'olawe. The declines elsewhere roughly correlated to rising human populations, but because Moloka'i's population was relatively low and stable, excessive runoff was believed to be a major factor.

• Within 990 feet of the shoreline between Kaunakakai Wharf and Kamalo, turbidity levels in April 2005 greatly exceeded what is commonly believed to be the upper threshold for maintaining healthy reefs. At many sites closer to shore, sediment concentrations topped levels found to be lethal at other reefs.

• One section of an otherwise thriving fore reef (the area beyond the crest that slopes into deeper waters and typically is the most lush) is virtually devoid of coral cover, suggesting that the sediment-related damage is spreading seaward.

'FUTURE IS IN JEOPARDY'

"Without protection of the reef from overuse and excess sedimentation, its future is in jeopardy," a report published last year by the U.S. Geological Survey concluded.

Feeter, who moved to Moloka'i from California almost 20 years ago, doesn't need the scientific data to realize something is seriously wrong.

When he first started windsurfing on the south shore in 1990, the retired veterinarian could see his feet as he waded in knee-deep water with his windsurfing equipment. Today, so much sediment is stirred up that all he sees is a murky mess.

"I just call it goo," Feeter said.

Moloka'i's runoff problem was serious enough that the U.S. Coral Reef Task Force about five years ago designated the south shore as a priority site in Hawai'i for addressing ways to combat land-based pollution.

Even before that, famed ocean explorer Jacques-Yves Cousteau in 1979 singled out Moloka'i as an example of excessive sedimentation harming reefs worldwide. He noted a long history of land-use practices on Moloka'i that contributed to the reef's degradation.

"With the arrival of Westerners, upland soil was plowed for sugar cane and pineapple," Cousteau wrote. "The impact of the resulting erosion has been tragic. Since 1897, the shoreline of Moloka'i has advanced as much as a mile and a quarter across the reef flat. Elsewhere off Moloka'i, the reef is overlaid with four to 27 inches of red-brown silt."

Mike Field, a USGS senior marine geologist who is one of the lead researchers on the ongoing Moloka'i studies, said the chocolate-colored water off the south shore is a chronic condition. The sediment is stirred up daily as the tide rises and when the trade winds are blowing, and the repeated suspensions tend to magnify damage to the reef many times over.

RECURRING PROBLEM

The sediment won't necessarily kill the corals, Field said, but the organisms become so stressed that they devote less energy to reproduction and other vital functions and become more susceptible to other threats.

Field said the sediment appears to remain on the reef for about 10 years before being flushed to the open sea, only to be replaced by still more mud coming off the coast.

"It's just a recurring problem, and it gets worse and worse after every rainstorm," said Ed Misaki, Moloka'i program director for The Nature Conservancy, an environmental group that is working with other organizations, the state and landowners to reduce erosion.

Through those efforts, about 12 miles of fencing have been put up to keep feral goats from stripping more vegetation from mountains.

Special hunting excursions, including aerial shoots, have been organized to try to reduce the thousands of goats that roam the south slopes. Proposals to build sediment retention ponds along drainage outlets have been discussed, but lack of funding is an obstacle.

The measures have generated some resistance, especially among hunters who believe their ability to put food on their tables has been impaired.

Ron Rapanot Sr., 69, president of Moloka'i Hunters Association, said he still isn't convinced that the damage to the reef is as severe as some have indicated. What's more, he added, Moloka'i's natural resources always have had the ability to bounce back.

"If they can prove to us the causes (of the damage), I know hunters wouldn't mind being involved" in finding solutions, Rapanot said.

Scientists say Moloka'i's people hold the key to the fate of the reef.

"It is largely through local decisions and local actions that protection of coral reefs can be assured for future generations," Field and several of his colleagues wrote in the Moloka'i USGS report.