“Survival of the fittest,” a phrase coined by Darwinian evolutionary theory, underscores the remarkable ability of living organisms to adapt to their changing environments and there is seldom better examples of just that than sharks. Sharks have called our ocean home for millions of years, their survival a testament to the marvels of evolution. With modern-day sharks comprising of at least 500 different species, all have evolved unique features to thrive in diverse habitats. One such adaptation that has captured the attention of scientists and engineers alike is their skin, specifically the tiny tooth-like structures known as denticles.
Each species boasts a distinct denticle morphology tailored to its specific lifestyle and environment. But their these denticles actually have unique shapes, sizes, and arrangements on a single species, too, highlighting that they serve a multitude of functions crucial for the shark’s survival. Past research has shown the denticles not only enhance hydrodynamics, allowing sharks to glide effortlessly through the water with minimal drag, but also exhibit remarkable antifouling properties, preventing the accumulation of marine organisms on their skin. Scientists have long been intrigued by the multifunctionality of shark skin denticles, delving into their hydrodynamic, antifouling, aerodynamic, protective, and bioluminescent attributes. However, until recently, research tended to focus narrowly on specific functions, overlooking the synergies between them. In a groundbreaking review, researchers have collated dermal denticle findings across various disciplines, providing a holistic understanding of their functionalities.
For example, they found one area that is ripe for exploration is the protective function of denticles, which remains relatively understudied. New research focusing on the whitespotted bamboo shark (Chiloscyllium plagiosum) offers intriguing insights into this lesser-known aspect of shark biology. Living among reefs and rocks, whitespotted bamboo sharks are renowned for their unique ability to “walk” along the ocean floor. However, they also engage in an intriguing behavior called “station holding,” where they rest on the ocean floor with their head lifted and pectoral fins positioned to create negative lift, allowing them to remain grounded. This “walking” lifestyle exposes their body – such as the snout, ventral areas, and pectoral fins – to continuous contact with abrasive substrates. Researchers measured the hardness and reduced elastic modulus of denticles from six body locations: the snout, flank regions above and below the pectoral fin, anterior edge of the pectoral fin, ventral region between the pectoral fins, and the caudal peduncle. Nanoindentation tests revealed that denticles from regions likely to experience greater mechanical stress, such as the snout, belly, and pectoral fin, exhibited higher values of hardness and reduced elastic modulus compared to flank regions. This suggests that denticles in these areas are functionally adapted to withstand higher mechanical stresses associated with their benthic lifestyle. Their analysis also showed a relatively uniform mechanical property distribution in the enameloid region of denticles from the snout, belly, and pectoral fin regions, indicating a consistent level of protection across these body areas.
These findings, the authors argue, hint at the existence of structural design strategies within shark denticles that contribute to their enhanced mechanical properties. However, further investigations are needed to fully understand the microstructure of these denticles and unveil the mechanisms behind their improved mechanical performance. The implications of this research extend far beyond the realm of marine biology, offering valuable insights for various industries. From marine vehicles and wind turbine blades to water filters and swimsuits, the multifunctional properties of shark skin denticles hold immense potential for enhancing performance, efficiency, and durability. And it doesn’t stop there, with dermal denticles influencing the appearance of bioluminescent sharks, opening new avenues for biomimetic designs in optical engineering and camouflage technology.
But will these animals be around for us to learn from them? Denticle corrosion caused by ocean acidification conditions has been found in a demersal shark species for the first time, and damage can impair a shark’s prey-catching ability, while scale corrosion reduces swimming efficiency. If widespread denticle corrosion caused by ocean acidification were to occur among shark populations, it would likely have significant repercussions on their survival and ecosystem dynamics. Beyond ecological scenarios, the decline of shark populations could have significant economic and social implications; sharks are valuable assets in fisheries, tourism, and scientific research, contributing to livelihoods, economies, and cultural heritage in many coastal communities. A massive decline in their populations could majorly disrupt these industries, leading to job losses, decreased revenue, and loss of Traditional knowledge and practices associated with shark conservation and management.
As ocean acidification intensifies, countless marine species and entire ecosystems (such as coral reefs) will face significant challenges in adapting to the changing conditions. Emerging electrochemical technology offers the potential to reverse ocean acidification, but until that is feasible to carry out in a widespread scale, urgent action is needed to address the underlying drivers of ocean acidification. Otherwise not only will we lose an iconic species… but the possibilities that come from what their evolutionary genius has to teach us.
