Blue mussels 'hang on' along rocky shores: For how long?

March 22, 2013 by Cheryl Dybas, National Science Foundation
Blue mussels anchor to rocks with byssal threads, now affected by ocean acidification. Credit: Emily Carrington/UW

Imagine trying to pitch a tent in a stiff wind. You just have it secured, when a gale lifts the tent—stakes and all—and carries it away.

That's exactly what's happening to a species that's ubiquitous along the rocky shores of both the U.S. West and East Coasts: the blue mussel.

Mussels make use of what are called byssal threads—strong, silky fibers—to attach to rocks, pilings and other hard substrates. They produce the threads using byssus glands in their feet.

Now, scientists have discovered, the effects of ocean acidification are turning byssal threads into flimsy shadows of their former selves, leaving mussels tossed about by wind and waves.

At high levels of —levels in line with expected concentrations over the next century—byssal threads become weaker, less able to stretch and less able to attach to rocks, found scientists Emily Carrington, Michael O'Donnell and Matthew George of the University of Washington.

The researchers recently published their results in the journal Nature Climate Change; O'Donnell is the lead author.

Oceans turning caustic

The pH of the seas in which these and other marine species dwell is declining. The waters are turning more acidic (pH dropping) as Earth's oceans change in response to increased carbon dioxide in the atmosphere.

As atmospheric carbon rises as a result of human-caused , carbon in the ocean goes up in tandem, ultimately resulting in ocean acidification, scientists have found.

To study the effects of ocean acidification on marine organisms, Carrington has been awarded an NSF SEES (Science, Engineering, and Education for Sustainability) Ocean Acidification grant.

"We need to understand the chemistry of ocean acidification and its interplay with other marine processes—while Earth's seas are still hospitable to life as we know it," says David Garrison, program director in NSF's Division of Ocean Sciences. "In the rocky intertidal zone, are at the heart of those processes."

Land between the tides

Visit the land between the tides, and you'll see waves crashing on boulders tinged dusky blue by snapped-closed mussels.

"Their shells are a soft color, the misty blue of distant mountain ranges," wrote Rachel Carson more than 50 years ago in her best-selling book The Edge of the Sea.

For blue mussels trying to survive, the rocky intertidal zone indeed may be akin to scaling a mountain range.

To discover the tenacity of mussels, scientists test maximum force needed to pull them free. Credit: Michael O'Donnell

The rocky intertidal is above the waterline at low tide and underwater at high tide—the area between tide marks.

It's home to such animals as starfish and sea urchins, and seaweed such as kelp. All make a living from what floats by rocky cliffs and boulders.

It can be a hard go. Rocky intertidal species must adapt to an environment of harsh extremes. Water is available when the tide washes in; otherwise residents of this no man's land between sea and shore are wide open to the elements.

Waves can dislodge them, and temperatures can run from scalding hot to freezing cold.

Hanging on for dear life

In the rocky intertidal, blue mussels hang on for dear life.

That may not always be the case.

Combining results from laboratory experiments with those from a mathematical model, Carrington and colleagues show that at high carbon dioxide concentrations, blue mussels can be dislodged by wind and wave forces 40 percent lower than what they are able to withstand today.

Mussels with this weakened ability, once dislodged from their homes, could cause ecological shifts in the rocky intertidal zone—and huge economic losses in a global blue mussel aquaculture industry valued at U.S. $1.5 billion each year.

"Mussels are among the most important species on rocky shores worldwide," says O'Donnell, "dominating ecosystems wherever they live. The properties in their byssal threads are also of interest to biochemists and have been studied as possible medical adhesives."

Blue mussels may make important contributions to the field of materials science, says Carrington.

"Some species of mussels are experts at gluing onto seagrass, some to other shells, some even adhere to rocks in the harsh conditions of deep-sea hydrothermal vents. Each may have different genes that code for different proteins, so the adhesives vary."

Will their potential be realized? Carrington, O'Donnell and George have found a disturbing answer.

The scientists allowed mussels to secrete byssal threads in a range of ocean water chemistries from present-day through predicted near-future conditions, then tested the threads to see how strong they were.

At levels considered reasonable for a near-future coastal ocean (given current rates of acidification), byssal threads were less able to stretch and therefore less able to adhere. Further testing revealed that the problem was caused by weakening of the glue where the threads attach to rocks and other hard surfaces.

Ocean acidification beyond shells and corals

"Much ocean acidification research has focused on the process of calcification," says Carrington, "through which animals and some plants make hard parts such as shells."

In acidifying oceans, that depend on calcium carbonate have a more difficult time forming shells or, in the case of coral reefs, skeletons.

"But there's more to marine communities than calcified parts," says O'Donnell. Other species such as mussels and their byssal threads, he says, are equally important.

"Understanding the broader consequences of requires looking at a variety of biological processes in a range of species."

A need that didn't exist when Rachel Carson wrote The Edge of the Sea.

"When we go down to the low-tide line, we enter a world that is as old as the Earth itself—the primeval meeting place," mused Carson, "of the elements of earth and water."

And of mussels and rock. Fifty years hence, will the mussels still be here?

Explore further: Researchers offer clues to how mussels work

Related Stories

Researchers offer clues to how mussels work

March 4, 2013

Waves slam the shore with the force of a jetliner screaming at 600 mph. Yet mussels - small but mighty denizens of the intertidal zone - still manage to cling tenaciously to their rocks.

Mussels cramped by environmental factors

February 16, 2013

The fibrous threads helping mussels stay anchored – in spite of waves that sometimes pound the shore with a force equivalent to a jet liner flying at 600 miles per hour – are more prone to snap when ocean temperatures ...

Zebra mussels hang on while quagga mussels take over

June 12, 2009

The zebra mussels that have wreaked ecological havoc on the Great Lakes are harder to find these days — not because they are dying off, but because they are being replaced by a cousin, the quagga mussel. But zebra mussels ...

Marine biodiversity loss due to warming and predation: study

November 28, 2011

The biodiversity loss caused by climate change will result from a combination of rising temperatures and predation – and may be more severe than currently predicted, according to a study by University of British Columbia ...

Recommended for you

Oceans of garbage prompt war on plastics

December 15, 2018

Faced with images of turtles smothered by plastic bags, beaches carpeted with garbage and islands of trash floating in the oceans, environmentalists say the world is waking up to the need to tackle plastic pollution at the ...

A damming trend

December 14, 2018

Hundreds of dams are being proposed for Mekong River basin in Southeast Asia. The negative social and environmental consequences—affecting everything from food security to the environment—greatly outweigh the positive ...

Data from Kilauea suggests the eruption was unprecedented

December 14, 2018

A very large team of researchers from multiple institutions in the U.S. has concluded that the Kilauea volcanic eruption that occurred over this past summer represented an unprecedented volcanic event. In their paper published ...

The long dry: global water supplies are shrinking

December 13, 2018

A global study has found a paradox: our water supplies are shrinking at the same time as climate change is generating more intense rain. And the culprit is the drying of soils, say researchers, pointing to a world where drought-like ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

2 / 5 (4) Mar 22, 2013
So, the mussels with threads that hang on better will survive and breed and take over those with weaker threads. Or some other animal will take over the niche. Twas ever thus, people get stressed over extinction way too much. What can survive, will survive.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.