New research on seaweeds shows it takes more than being flexible to survive crashing waves

May 10, 2012, American Journal of Botany
This image shows seaweeds reconfiguring in flow, viewed from downstream. Credit: Courtesy of Patrick Martone, University of British Columbia

Seaweeds are important foundational species that are vital both as food and habitat to many aquatic and terrestrial shore organisms. Yet seaweeds that cling to rocky shores are continually at risk of being broken or dislodged from their holds by crashing waves with large hydrodynamic forces. So how do such seaweeds survive in intertidal zones? Do they have special properties that make them extremely flexible or particularly strong?

Patrick Martone (University of British Columbia) has spent a considerable amount of time standing on the shore watching big waves crash against intertidal rocks and wondering how the —or anything else—manage to survive there.

"Many animals can run and hide when storms roll in and the waves increase," Martone observes. "But seaweeds don't have that option; they have to just hold on tight and face the waves head-on."

Indeed, the drift algae that pile up on the beach after a big storm suggest that not all algae are able to survive such onslaughts.

"So what is special about the ones that do survive?"

Previous research has found that one solution seaweeds have come up with is flexibility. Blades of seaweed may curl up and branches may collapse, thereby changing the shape of the seaweed and reducing drag as water velocity increases. But different seaweeds may utilize different strategies to effectively reduce drag, such that some may be better at changing shape and others at reducing size. Martone and colleagues from Stanford University and St. John Fisher College were interested in teasing apart some of these variables and published their findings recently in the American Journal of Botany.

By exploring the dynamics of size and shape changes of intertidal seaweeds at different rates of water flow, Martone and co-authors hoped to better understand the various strategies that have led to the morphological diversity in macroalgae seen along wave-swept shores.

The authors collected fronds from six different species of algae (four branched, two bladed) along the intertidal zone of the central Californian coast, placed them in a recirculating water flume, and measured the drag they experienced and the changes in shape and size they underwent under 15 different rates of water flow, ranging from 0 to 4 m/sec.

Interestingly, they found that while all six species of seaweed underwent severe reconfiguration as water velocity increased—thus limiting the drag they would otherwise experience if they were rigid—the two types of algae accomplished this in slightly different ways.

"Unbranched algae seem to be 'shape changers,' reducing drag primarily by folding and collapsing in flow," notes Martone. "Certain branched algae, on the other hand, are 'area reducers,' compensating for drag-prone shapes by reducing frond size through branch reorientation and compression. Thus, we demonstrate that flexibility acts in two distinct ways: permitting wave-swept algae to change shape and to reduce frond area projected into the flow."

Martone and colleagues also wanted to see how accurately responses at slow speeds of water flow could be extrapolated to what happens at higher speeds, such as what the seaweeds might be experiencing along the shore.

"Most structural engineers have it easy," Martone says. "Studying air flow around airplane wings or around bridges is relatively straightforward, since these man-made structures are rigid and do not deform in flow. Seaweeds are more complicated because they are flexible. As flow speeds increase, flexible seaweeds re-orient and reconfigure, changing size and shape to reduce drag, making predictions much more difficult."

Indeed, the authors found that measurements extrapolated out from lower speeds did not always match those observed at higher speeds, making it tricky to predict what would happen at higher water velocities. Moreover, in the experimental water flume seaweeds may have more time to react to water speeds that are relatively slow compared with breaking waves—a condition whereby fast reaction times may be crucial for reconfiguring and reducing drag.

"Understanding how selection can act on the ability to change shape or the ability to reduce size in flow may give us insight into the morphological evolution of intertidal algae," summarizes Martone.

Martone concludes that further investigation is still needed to tease these features apart: "We have started building flexible models of branched and unbranched seaweeds in the lab to explore how precise changes in branching affect drag. We hope this work will help us better understand how waves have sculpted seaweeds over evolutionary time."

Explore further: Billion-year revision of plant evolution timeline may stem from discovery of lignin in seaweed

More information: Patrick T. Martone, Laurie Kost, and Michael Boller. 2012. Drag reduction in wave-swept macroalgae: Alternative strategies and new predictions. American Journal of Botany 99(5): 806-815. DOI: 10.3732/ajb.1100541

Related Stories

Sydney harbors deadly diet for sea creatures

April 7, 2008

Contaminated seaweeds in Sydney Harbour could be threatening the small animals that feed on them, according to a new study revealing that the harbour's seaweeds have the world's highest levels of copper and lead contamination.

Seaweed records show impact of ocean warming

October 27, 2011

As the planet continues to warm, it appears that seaweeds may be in especially hot water. New findings reported online on October 27 in Current Biology, a Cell Press publication, based on herbarium records collected in Australia ...

Deep-sea algae may be 'living fossils'

November 19, 2010

(PhysOrg.com) -- Researchers in the US and Belgium say two types of deep-sea seaweed may be representatives of ancient forms of algae previously unrecognized.

Sea urchins cannot control invasive seaweeds

July 13, 2011

Exotic marine species, including giant seaweeds, are spreading fast, with harmful effects on native species, and are increasingly affecting the biodiversity of the Mediterranean seabed. Some native species, such as sea urchins ...

Recommended for you

In colliding galaxies, a pipsqueak shines bright

February 20, 2019

In the nearby Whirlpool galaxy and its companion galaxy, M51b, two supermassive black holes heat up and devour surrounding material. These two monsters should be the most luminous X-ray sources in sight, but a new study using ...

When does one of the central ideas in economics work?

February 20, 2019

The concept of equilibrium is one of the most central ideas in economics. It is one of the core assumptions in the vast majority of economic models, including models used by policymakers on issues ranging from monetary policy ...

Research reveals why the zebra got its stripes

February 20, 2019

Why do zebras have stripes? A study published in PLOS ONE today takes us another step closer to answering this puzzling question and to understanding how stripes actually work.

Correlated nucleons may solve 35-year-old mystery

February 20, 2019

A careful re-analysis of data taken at the Department of Energy's Thomas Jefferson National Accelerator Facility has revealed a possible link between correlated protons and neutrons in the nucleus and a 35-year-old mystery. ...

0 comments

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.