Flexible Anchor Prevents Peeling

light brown kelp seen in dramatic contrasting light

Biological Strategy

Kelp

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Attach Permanently

A living system can conserve energy by attaching permanently to a particular site because it can take advantage of resources that come its way, rather than expending energy to move to resources. A permanent attachment, intended to last the lifetime of the living system, creates special challenges. For example, physical mechanisms, such as the anchor that holds a marine algae to the ocean’s bottom, must be able to withstand forces that can pull it off its substrate. Chemical mechanisms, such as a barnacle’s glue, must avoid both physical and chemical breakdown, such as being dissolved by water.

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Manage Shear

The effect of shear stress on a living system is parallel internal surfaces sliding past each other. Slippage occurs in parallel with the force. Think about holding two wooden boards on top of each other and sliding one to the right and the other to the left. This may be easy until you add glue, which increases their shear strength and makes them harder or impossible to slide. Shear can occur in solids, liquids, and gases. Living systems must increase their shear strength to overcome these types of forces. For example, darkling beetles lock their wings together in flight to prevent lateral movement by using many small hairs on each wing. These hairs interlock to provide shear strength, just as two hair brushes put together would be difficult to slide past each other.

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Manage Turbulence

A turbulent force occurs when air or water creates a chaotic or irregular motion. The source can be such things as wind, waves, and eddies caused by obstructions to air or water flow (such as that created by a rock in a stream). Because the force is irregular, it acts in unpredictable ways on multiple parts of a living system at any given time, decreasing the living system’s efficiency. Strategies used to manage turbulence include dampening the amount of turbulence, having flexibility to handle sudden changes, and making quick adjustments. An example is the mucus on aquatic organisms, such as barracuda sharks, that can reduce turbulent friction of seawater by 66%. In doing so, it decreases drag and increases the sharks’ swimming efficiency.

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Plants

Phylum Plantae (“plants”): Angiosperms, gymnosperms, green algae, and more

Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.

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Flexible anchoring structures on many aquatic organisms avoid peeling by distributing forces over a larger area.

Living in or near the intertidal zone of a rocky seashore usually requires being good at holding on. Organisms that live in this habitat commonly deal with crashing waves and strong underwater flows that exert varying forces in all directions.

To withstand these forces, many intertidal organisms attach to rocks and other surfaces using parts that function as flexible anchors. These anchoring structures commonly consist of a roughly disc-shaped base that gradually tapers and becomes more flexible as it joins the main body. Examples include holdfasts on seaweeds and the feet of intertidal snails. When forces impact the anchor, the base is firmly attached while the rest of the structure can bend and deform slightly. This flexibility prevents forces from being concentrated at a small area on the anchor, a situation that increases the chances of peeling and detaching.

Image: Fitzgerald Marine Reserve docent / CC BY - Creative Commons Attribution alone

Image: Heiko Hübscher / CC BY SA - Creative Commons Attribution + ShareAlike

Last Updated September 5, 2018

References

“Loads that might cause peeling occur widely in nature. Neither the holdfast of a large marine alga nor the byssal thread of an intertidal mussel nor the foot of the wave-challenged snail can be assured of tensile forces perpendicular to its attachment surface. All respond with some tapering disk of attachment that’s increasingly flexible peripherally (fig. 21.1b)–the whole thing distorts a little to avoid stress concentrations at an edge. Thus, a good shape for a glued joint may resemble (and may also function as) a suction cup, even though the two mechanisms are physically distinct.” (Vogel 2003:425)

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Comparative Biomechanics: Life's Physical World, Second Edition

17/06/2013 | Steven Vogel

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