Buttresses of Red Mangrove Improve Stability

green trees with red roots on beach during the daytime

Biological Strategy

Red mangrove

Eleanor Banwell

Image: eye-blink / Shutterstock / Some rights reserved

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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Protect From Excess Liquids

While water is essential to life, too much water or other liquids can overwhelm living systems. Excess liquids can, for example, decrease a living system’s access to oxygen, promote excessive bacterial or fungal growth, or strip away soil and nutrients. To prevent the accumulation of excess liquids, living systems must control the movement of liquids across their boundaries or surfaces. They do so using waterproofing materials or structures, slowing flow, and/or facilitating flow to move the liquid away. Plant leaves, for example, commonly have waxy surfaces comprised of water-repelling chemicals to keep water from engorging the leaves or facilitating bacterial and fungal growth.

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Protect From Wind

Wind subjects living systems to various forces, such as compression, twisting, turbulence, and tension. These forces put living systems at risk of losing the ability to perform life-essential functions, such as when a plant becomes uprooted. Wind can result from weather phenomena or rapid movement through the air, as when flying. Wind is typically not a constant or predictable force, so living systems must be able to function both with and without its presence by adjusting to its direction and speed. A good example is how plants’ leaves and stems are flexible so that they can align with the wind, rather than being battered by it.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Buttresses of the red mangrove enable growth in thin soils by efficiently increasing footprint

The red mangrove (Rhizophora mangle) is a coastal tree that grows in shallow estuaries throughout tropical regions. They grow in regions where storms and high winds are common and they are continually subjected to water currents and tidal forces. At the same time, they grow in waterlogged and shallow silt that is continually moving and so they are unable to anchor themselves using their roots the way trees growing on land can. Unsurprisingly, these trees invest much less energy in their root system, which can be as low as 5% of the total tree biomass (this compares to between 15-55% for other tree species). Instead, red mangrove trees rely on rhizophora, specialised stilts made from the same material as the main stem that take in and transport water and oxygen and also provide support for the tree on a difficult shifting surface.

Red mangrove rhizophora work like flying buttresses on European cathedrals, or like a person using ski poles or crutches to maintain balance. They make the footplate area of the organism much larger, whilst keeping down the total amount of tissue required for stability. Red mangle buttresses are even more effective at this than man-made structures, as their rhizophora branch as many as six times before entering the silt.

As the trees grow, new rhizophores are continually produced, enabling the trees to respond to changes in their environment, for example growing towards the best light, regardless of the quality of the substrate. They are remarkably effective at this, growing larger than other trees in the mangrove forests and maintaining main stems that are no more than a few degrees from vertical, despite the challenging conditions and continual pressure from water flow and tides that constantly threaten to push them over.

The unique structure and stability of the red mangrove makes them particularly important for the protection of vulnerable coastal ecosystems from extreme events like cyclones and tsunamis.

Image: James St. John / CC BY SA - Creative Commons Attribution + ShareAlike

Image: Photo by CEphoto, Uwe Aranas / CC BY SA - Creative Commons Attribution + ShareAlike

Last Updated August 14, 2020

References

Journal article

Root biomechanics in Rhizophora mangle: anatomy, morphology and ecology of mangrove’s flying buttresses.

Ann. Bot. | Méndez-Alonzo R, Moctezuma C, Ordonez VR, Angeles G, Martinez AJ, Lopez-Portillo J

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