Mark Denny has spent most of his research career puzzling over life on the seashore. And when he describes the pounding that these organisms get almost every moment of their lives, you begin to understand why. If you were constantly battered by hurricane force winds, you'd want armour too, just like the limpets that cling to rocky shorelines. But some organisms have developed a more flexible approach for surviving one of the planet's harshest environments. In their review: The mechanics of wave-swept algae(p. 1355), Denny and his colleague Brian Gaylord, describe the successful pact that the algae have made with their turbulent environment to ensure their survival.
All sea algae grow along the same body plan. Each has a pad-like-anchor that tethers them to the rock with thousands of tiny finger like projections that grip on to tiny fissures in the rock's surface. A slender flexible stem,called a stipe, grows out of the `holdfast' structure and frilly `blades' grow from the stipe.
At first sight, kelp doesn't look as if it could survive a sharp tug,let-alone a constant assault from the sea. Denny explains that if you told an engineer that you could build a 30m long elastic band that could survive hurricane forces, he wouldn't believe you. But just a few metres off the coast, giant kelp wave in the sea, and that's exactly what they are. He says that even though algae are relatively flimsy `they do a remarkable job of coping'.
One of the algae's strategies for survival is to use their flexibility to`go with the flow' in strong currents. They align with the prevailing flow to reduce the damaging drag on the algae's delicate fronds. But this relaxed approach comes at a price. Algae that drift with the prevailing current eventually reach a point when they can't extend any further, and have effectively reached the end of their tether. At the last moment, as the algae reaches its limit, the algae's own weight can be enough to wrench the stipe away from its holdfast.
The review also describes the forces the algae experience as a result of the ocean's constant movement. Algae that live in relatively deep water experience weak forces from unbroken rolling waves, so they have a relatively quiet life. But it's a different matter altogether in the surf zone, where water velocities suddenly double as the wave breaks. Denny and Gaylord point out that the next major question is understanding how exposed algae at the sea's edge survive the huge forces produced by breaking waves; these are the strongest forces that the plants will ever encounter.
Understanding the algae's intriguing resilience is an important step along the way to conserving this economically significant crop. Kelp forests are the preferred spawning grounds for many major fish stocks, and the algae are also harvested to supply alginates to the food and cosmetics industry. Recent fluctuations in the planet's climate have caused an increase in the frequency of El Niño events that warm the southern oceans and increase the number of storms the algae have to contend with. Understanding how these plants weather today's storms could help us design marine reserves if climate change threatens to take the algae beyond their elastic limit.