Moreton Bay, Australia — The fireweed began each spring as tufts of hairy growth and spread across the seafloor fast enough to cover a football field in an hour.
When fishermen touched it, their skin broke out in searing welts. Their lips blistered and peeled. Their eyes burned and swelled shut. Water that splashed from their nets spread the inflammation to their legs and torsos.
"It comes up like little boils," said Randolph Van Dyk, a fisherman whose powerful legs are pocked with scars. "At nighttime, you can feel them burning. I tried everything to get rid of them. Nothing worked."
As the weed blanketed miles of the bay over the last decade, it stained fishing nets a dark purple and left them coated with a powdery residue. When fishermen tried to shake it off the webbing, their throats constricted and they gasped for air.
After one man bit a fishing line in two, his mouth and tongue swelled so badly that he couldn't eat solid food for a week. Others made an even more painful mistake, neglecting to wash the residue from their hands before relieving themselves over the sides of their boats.
For a time, embarrassment kept them from talking publicly about their condition. When they finally did speak up, authorities dismissed their complaints -- until a bucket of the hairy weed made it to the University of Queensland's marine botany lab.
Samples placed in a drying oven gave off fumes so strong that professors and students ran out of the building and into the street, choking and coughing.
Scientist Judith O'Neil put a tiny sample under a microscope and peered at the long black filaments. Consulting a botanical reference, she identified the weed as a strain of cyanobacteria, an ancestor of modern-day bacteria and algae that flourished 2.7 billion years ago.
O'Neil, a biological oceanographer, was familiar with these ancient life forms, but had never seen this particular kind before. What was it doing in Moreton Bay? Why was it so toxic? Why was it growing so fast?
The venomous weed, known to scientists as Lyngbya majuscula, has appeared in at least a dozen other places around the globe. It is one of many symptoms of a virulent pox on the world's oceans.
In many places -- the atolls of the Pacific, the shrimp beds of the Eastern Seaboard, the fiords of Norway -- some of the most advanced forms of ocean life are struggling to survive while the most primitive are thriving and spreading. Fish, corals and marine mammals are dying while algae, bacteria and jellyfish are growing unchecked. Where this pattern is most pronounced, scientists evoke a scenario of evolution running in reverse, returning to the primeval seas of hundreds of millions of years ago.
Jeremy B.C. Jackson, a marine ecologist and paleontologist at the Scripps Institution of Oceanography in La Jolla, says we are witnessing "the rise of slime."
For many years, it was assumed that the oceans were too vast for humanity to damage in any lasting way. "Man marks the Earth with ruin," wrote the 19th century poet Lord Byron. "His control stops with the shore."
Even in modern times, when oil spills, chemical discharges and other industrial accidents heightened awareness of man's capacity to injure sea life, the damage was often regarded as temporary.
But over time, the accumulation of environmental pressures has altered the basic chemistry of the seas.
The causes are varied, but collectively they have made the ocean more hospitable to primitive organisms by putting too much food into the water.
Industrial society is overdosing the oceans with basic nutrients -- the nitrogen, carbon, iron and phosphorous compounds that curl out of smokestacks and tailpipes, wash into the sea from fertilized lawns and cropland, seep out of septic tanks and gush from sewer pipes.
Modern industry and agriculture produce more fixed nitrogen -- fertilizer, essentially -- than all natural processes on land. Millions of tons of carbon dioxide and nitrogen oxide, produced by burning fossil fuels, enter the ocean every day.
These pollutants feed excessive growth of harmful algae and bacteria.
At the same time, overfishing and destruction of wetlands have diminished the competing sea life and natural buffers that once held the microbes and weeds in check.
The consequences are evident worldwide.
Off the coast of Sweden each summer, blooms of cyanobacteria turn the Baltic Sea into a stinking, yellow-brown slush that locals call "rhubarb soup." Dead fish bob in the surf. If people get too close, their eyes burn and they have trouble breathing.
On the southern coast of Maui in the Hawaiian Islands, high tide leaves piles of green-brown algae that smell so foul condominium owners have hired a tractor driver to scrape them off the beach every morning.