Giant, Mucus-Like Sea Blobs on the Rise, Pose Danger

Christine Dell'Amore
National Geographic News

October 8, 2009
Beware of the blob—this time, it's for real.

As sea temperatures have risen in recent decades, enormous sheets of a mucus-like material have begun forming more often, oozing into new regions, and lasting longer, a new Mediterranean Sea study says.

And the blobs may be more than just unpleasant.

Up to 124 miles (200 kilometers) long, the mucilages appear naturally, usually near Mediterranean coasts in summer. The season's warm weather makes seawater more stable, which facilitates the bonding of the organic matter that makes up the blobs.

Now, due to warmer temperatures, the mucilages are forming in winter too—and lasting for months.

Until now, the light-brown "mucus" was seen as mostly a nuisance, clogging fishing nets and covering swimmers with a sticky gel—newspapers from the 1800s show beach-goers holding their noses, according to study leader Roberto Danovaro, director of the marine science department at the Polytechnic University of Marche in Italy.

But the new study found that Mediterranean mucilages harbor bacteria and viruses, including potentially deadly E. coli, Danovaro said. Those pathogens threaten human swimmers as well as fish and other sea creatures, according to the report, published September 16 in the journal PloS One.

Blobs Born of "Marine Snow"

A mucilage begins as "marine snow": clusters of mostly microscopic dead and living organic matter, including some life-forms visible to the naked eye—small crustaceans such as shrimp and copepods, for example.

Over time, the snow picks up other tiny hitchhikers, looking for a meal or safety in numbers, and may grow into a mucilage.

The blobs were first identified in 1729 in the Mediterranean, where they're most often seen. The sea's relative stillness and shallowness make the water column more stable, providing ideal conditions for mucilage formation.

For the new study, Danovaro and colleagues studied historical reports of mucilage in the Mediterranean from 1950 to 2008. Outbreaks, they discovered, were more likely when sea-surface temperatures were warmer than average.

Swimming Into "Mucus"

In 1991, Italian marine biologist Serena Fonda Umani swam alongside a mucilage—the mass is too dense to swim inside—in the Adriatic Sea, an arm of the Mediterranean.

She remembers diving about 50 feet (15 meters) down when she got the sensation of a ghost floating over her—"sort of an alien experience."

Umani, a co-author of the new study with Danovaro and Antonio Pusceddu, of the Polytechnic University of Marche, has also dived into marine snow—the mucilage's precursor.

She described it like swimming through a sugar solution. Out of the water, the dried "sugar" stiffened her hair and stuck to her wetsuit.

"The suit was impossible to wash totally, because it was covered by a layer of greenish slime," said Umani, of Italy's University of Trieste. "It was a nightmare."

Few people would purposely swim into a mucilage, said Farooq Azam, a marine microbiologist at the University of California's Scripps Institution of Oceanography.

"If you were not familiar with this—and especially if you were familiar—you wouldn't want to go near it," said Azam, who was not involved in the new study.

A giant odiferous blob drifting offshore is "certainly not the seascape that one goes to the beach [for]," Azam added.

Public Health Hazard

Eager to see if the blobs' side effects extend beyond ruined wetsuits, Umani and colleagues sampled coastal waters and mucilage from the Adriatic in 2007. The warm, shallow sea is like a "big bathtub," Scripps's Azam said—an ideal natural laboratory for studying the blobs.

The study team discovered that the blobs are hot spots for viruses and bacteria, including the deadly E. coli. Coastal communities regularly test for E. coli, and its presence is enough to close beaches to swimming.

Study leader Donavaro said, "Now we see that … the release of pathogens from the mucilage can be potentially problematic" for human health.

People who swim through mucilage can also develop skin conditions such as dermatitis, he added.

Suffocated by Blobs

Fish and other marine animals that have no choice but to swim with mucilages are most vulnerable to their disease-carrying bacteria, which can kill even large fish, the study says.

The noxious masses can also trap animals, coating their gills and suffocating them, Danovaro said.

And the biggest blobs can sink to the bottom, acting like a huge blanket that smothers life on the seafloor.

Mucilages Going Global?

Mucilages aren't a concern for just the Mediterranean, Danovaro added. Recent studies tentatively suggest that mucus may be spreading throughout oceans from the North Sea to Australia, perhaps because of rising temperatures, he said.

"It's a good example [of what will happen if] we don't do something to stop climate warming," Danovaro said. "There are consequences [if] we continue to deny the scientific evidence."

Beyond warm temperatures, it's still not exactly clear what drives the blobs' formation, Scripps' Azam pointed out. For instance, no one knows why the dead marine matter in the blobs doesn't decompose.

"It's important we do find out" what's driving the rise of the blobs, Azam said, "for the sake of the rest of the worlds' oceans."