Extremely Aggressive Seaweed Just Ate an Entire Coral Reef

The world's coral reefs may have something new to worry about.

Bursts of sunlight streaming through underwater kelp forest at Anacapa Island in the Channel Islands National Park.
Seaweed, like this kelp forest, naturally covet sunlight.

Douglas Klug / Getty Images 

A newly discovered form of algae that looks a lot like a tumbleweed rolled up on a pristine coral reef north of Hawaii — and feasted on it.

Even more alarming, the reef, which is part of the protected 2,000-mile Northwestern Hawaiian Islands marine habitat, may only be an appetizer.

In a study published this week in the journal PLOS One, researchers at the University of Hawaii describe a hyper-aggressive new breed of seaweed that chokes out coral.

Essentially, the seaweed, which is a kind of algae that snaps off and rolls along the ocean floor, crowds coral neighborhoods, soaking up all the sunlight and starving coral of nutrients. Think of something along the lines of the infamous kudzu monster that blankets the American South.

"This is a highly destructive seaweed with the potential to overgrow entire reefs," study co-author Heather Spalding tells the Associated Press. “We need to figure out where it's currently found, and what we can do to manage it."

The reef-killer first reared its head in 2016, the organization reports, during a scientific survey of Pearl and Hermes Atoll. At the time, it appeared only as negligible clumps of seaweed. But a second survey last summer revealed its astonishing appetite for coral destruction. The seaweed had expanded to cover an entire reef in as much as eight-inches of impenetrable thicket.

"Everything underneath of it was dead," Spalding recalls.

And so too went the neighborhood. The researchers noted an eerie absence of life — the myriad creatures that once made the 15-mile atoll a bustling marine metropolis.

Grim Tidings for an Entire Archipelago

If this hungry kudzu of the sea goes unchecked, researchers warn the entire Papahanaumokuakea Marine National Monument — a vast protected marine environment — could be on the menu.

“We have, not until now, seen a major issue like this where we have a nuisance species that's come in and made such profound changes over a short period of time to the reefs," Alison Sherwood, chief scientist on the study, adds.

Of course, coral reefs have enough problems without killer tumbleweed showing up on the scene. About half of Australia’s Great Barrier Reef, for example, has been declared dead, with scientists suggesting the other half could meet the same fate by 2050. What’s eating the world’s largest coral reef system is also taking a toll on other reefs throughout the world. Notably, rising sea temperatures — thanks much to human-induced climate change — is resulting in widespread coral bleaching. That’s when environmental stresses weaken coral, leaving it vulnerable to disease.

Oceans also absorb a lot of the carbon dioxide that we churn into the atmosphere, altering the water’s chemistry and creating a more acidic environment. 

Even sunscreen — thanks to the common ingredient oxybenzone — can ravage a reef

In one study, researchers found that just a small amount of sunscreen containing the ingredient oxybenzone could be enough to break down coral, causing it to lose its nutrients. Fortunately, there are plenty of options that don’t contain the coral-weakening ingredient.

The coral systems of the Northwestern Hawaiian Islands, at least, don’t have to stress sunscreen. Humans don’t often frequent the Pearl and Hermes Atoll, which lies in the middle of the Pacific, some 2000 miles from Asia and North America.

On the other hand, there is a certain seaweed that rolls into reefs and puts coral in a kudzu-like chokehold — a marauder that has scientists a half a world away more than a little concerned.

“When you see something unusual in the last few years, you can be pretty sure that this is something that's a bit special as opposed to just things that change from year to year,” marine biologist Peter Mumby, who was not involved with the latest study, tells AP. “But it is a matter of concern whenever you see an ecosystem start to display symptoms ... like this.”