HANALEI, Hawaii — When compiling a list of places that may be described as paradise, Hanalei Bay on the rugged north shore of the island of Kauai surely qualifies.
The perfect crescent bay, rimmed by palm trees, emerald cliffs and stretches of white sand, has always had a dreamy kind of appeal. It was on these shores that sailors in the movie "South Pacific" sang of the exotic but unattainable "Bali Ha'i."
The problem is what lies below the surface of the area's shimmering blue waters.
Since June, a mysterious milky growth has been spreading rapidly across the coral reefs in Hanalei and the surrounding bays of the north shore — so rapidly that biologist Terry Lilley, who has been documenting the phenomenon, says it now affects 5% of all the coral in Hanalei Bay and up to 40% of the coral in nearby Anini Bay. Other areas are "just as bad, if not worse," he said.
The growth, identified by scientists at the U.S. Geological Survey as both a cyanobacterial pathogen — a bacteria that grows through photosynthesis — and a fungus, is killing all the coral it strikes, and spreading at the rate of 1 to 3 inches a week on every coral it infects.
"There is nowhere we know of in the entire world where an entire reef system for 60 miles has been compromised in one fell swoop. This bacteria has been killing some of these 50- to 100-year-old corals in less than eight weeks," Lilley said. "Something is causing the entire reef system here in Kauai to lose its immune system."
The discovery of the new coral disease is only one of a number of ailments afflicting nearly all the world's coral reefs, which are threatened by poisonous runoff, rising oceans, increasingly acidic waters and overfishing.
But this one could jeopardize a multibillion-dollar tourist industry in Hawaii, which depends on the stunning displays of color and wildlife for divers and snorkelers. That is especially true along the beaches of Kauai, where the north shore with a few exceptions remains a place of pristine natural beauty.
"It's very alarming," said Wendy Wiltse of the federal Environmental Protection Agency in Honolulu. "All of us are concerned about it. We want to do more. Part of the problem is we don't know what to do, especially in the case of a disease that's spread by a pathogen. It's not like we can put antibiotics in the ocean."
Researchers at the U.S. Geological Survey reported last week that the disease had reached epidemic proportions. "This is the first time a cyanobacterial/fungal disease on this scale has been documented in Hawaiian corals," Thierry M. Work, USGS wildlife disease specialist, said in an analysis released Wednesday.
Scientists say there are no signs so far that the bacteria killing the coral are dangerous to humans or wildlife, though they are conducting further tests.
But Lilley, who does not hold a graduate degree but dives daily around the reefs all across the north shore, said he has documented a large number of cases of black-and-white toby fish feeding near diseased corals that turned completely black, lost their fins and died.
He has also videotaped a sea turtle, seen feeding on seaweed growing out of an infected coral, whose eyes seemed to have rotted away. When Lilley saw it, the creature was bumping blindly into the reef in an attempt to find food.
The disease was first spotted around Hanalei in 2004, but "at very low levels," and is the fourth coral disease outbreak documented in the state since 2009, said Greta Aeby, a coral expert with the University of Hawaii Institute of Marine Biology who has been working with Lilley to document the phenomenon.
"Hawaii's reefs are in decline. They are faced with the chronic stressors of land-based pollution, overfishing and human use. The reefs have been dealing with these problems for years, and are starting to show the signs," she said. "We need to help people understand the seriousness of the situation before it is too late."
Lilley said the rapid growth of the coral disease this year followed two years of heavy sedimentation traveling down the Hanalei River, which he believes could be traced to development upstream and heavy rains.
Thick mud often coated the corals, he said, and studies paid for by a community group showed high levels of heavy metals in the water — studies that were dismissed by the state Department of Health, which said such metals were natural to the volcanic soil of Hawaii.
Wiltse said other studies had shown high levels of sewage-related bacteria in the Hanalei River, probably because the town of Hanalei has no sewer system and homes are connected to cesspools and septic systems.
"There have also been some studies of sediment and nutrients, primarily in Hanalei River, and during rain events, there is excessive suspended sediment in the river, exceeding water quality standards," she said. "I've seen plumes extending into the ocean. I've seen sediment settling on corals."
But is that what led to the recent outbreak of a bacterial infection? No one can say. Lilley theorizes that pollution could have weakened the coral and made it more susceptible to a bacterial outbreak, but can't be certain.
In a preliminary review in September, the USGS said the general health of coral reefs along Kauai's north shore was poor. "The overall picture was one of a severely degraded reef impacted by sediments and turf algae," the agency's report said, with symptoms of "chronic stress."
Work, the USGS scientist, said the loss of coral meant a danger of losing the fish, turtles and various invertebrates that depend on it for sustenance and shelter.
"A lot of people come to Hawaii in part because it is a beautiful place both on land and in the water, so coral reefs are a resource with tangible economic value," he said. "Like it or not, ecosystem health is closely intertwined with human and animal health."