Great Barrier Reef Awash With Horror Stories : Australia: Pollution, oil spills, overfishing and more than a million tourists a year threaten the coral and furrow the brows of scientists and environmentalists.

The Great Barrier Reef, one of the world’s natural wonders, is awash in a sea of worries.

Threats posed by pollution, oil spills, overfishing and more than a million tourists a year furrow the brows of scientists and environmentalists.

Protected as the Great Barrier Reef Marine Park since 1975, the reef encompasses about 135,000 square miles, an area larger than Great Britain. It is a feature so grand that it can be seen from orbiting spacecraft.

The largest system of coral and associated plants and animals in the world, the Great Barrier Reef is actually a 1,250-mile-long complex of 2,900 separate reefs off the northeast Australian coast. The reef’s turquoise waters shelter 1,500 species of fish, 400 types of coral and 4,000 species of mollusks.

With so much at stake, reef experts have become increasingly uneasy in the last few years as some coastal waters off Australia’s Queensland state have become murkier. Water quality in the park is described as “a critical management issue.”

A recent study indicates that runoff from Queensland’s rivers washes 16.5 million tons of sediment into the Coral Sea each year. Mixed with this runoff are nearly 85,000 tons of nitrogen and 11,000 tons of phosphorous, much of it from fertilizers used on farms.

In adverse wind and tidal conditions, river runoff can carry harmful chemicals 125 miles offshore. In the sea, nitrogen and phosphorous enhance the growth of algae known as phytoplankton.

The green glop blocks the sunlight that nurtures coral and other reef creatures. “Phosphorous actually damages the coral’s skeleton, making it weaker and more prone to damage from storms,” said Jon Brodie, director of research for the Great Barrier Reef Marine Park Authority.

Scientists from several Australian organizations have joined a four-year study to learn precisely where the nutrients are coming from, how they reach different parts of the reef and how they interact in various reef environments.

More ominous than algae, however, is the constant threat of oil spills. About 2,000 ships, 200 of them tankers, pass close to the Great Barrier Reef each year.

Freighters, too, carry oil or oil products. Big bauxite and coal ships sometimes carry 2,000 to 3,000 tons of fuel oil. So when any vessel collides or runs aground, there is the possibility of an oil spill, from minor to catastrophic. Deliberate pumping of waste oil directly into the ocean causes many small spills.

“It’s impossible for a single event to wipe out the entire reef system, but a 40,000-ton spill similar to the Exxon Valdez could wipe out a significant chunk of it,” said the park authority’s reef-monitoring expert, Steve Raaymakers.

“In a worst-case scenario, we’re talking about oiling 125 to 185 miles of coastline, 50 reefs and about 50 islands--roughly 10% of the total reef area.”

Even the ballast water carried aboard foreign ships worries Wendy Craik, the park authority executive officer. This water is often expelled after the vessels reach Australian ports. “All you need is one nasty organism released with that water, and the effects on our coral could be irreversible,” Craik said.

Scientists also are evaluating the effect that hordes of tourists have on the reef. Huge, sleek, aluminum-hulled catamarans slice through the waves every day, chockablock with goggle-eyed visitors eager to try out their first snorkel and fins.

Inevitably, some of the snorkelers break delicate coral formations. Their sheer numbers cloud the waters.

Anchors and chains dropped by commercial trawlers and weekend sailors take a further toll on coral. Heavy nets dragged over the bottom rake wide areas. John Robertson, who monitors fishing for the park authority, expresses “a major concern that trolling is modifying the sea bottom.”

The heavy fishing also seems to be affecting various species on the reef. Commercial operators go after easily marketable catches such as prawns.

“The rest that turns up in the nets goes over the side as dead matter, which attracts big, predatory fish such as sharks,” said Robertson. These carnivorous marauders seem to be taking over some areas once dominated by herbivorous fish.

As if all that weren’t enough to worry about, the crown-of-thorns starfish seems to be acting up again.

A starfish outbreak in the late 1970s devastated large portions of the reef, then suddenly subsided. But now the park’s starfish authority, Brian Lassig, is getting reports of growing numbers of crown of thorns near the resort center of Cairns, where the last infestation started.

A notorious glutton, the spine-covered menace dines on coral. In a single day it can graze an area twice the diameter of its body.

A predilection for fast food seems to be the predator’s one redeeming feature. It seems to prefer coral that can regrow in about 15 years.