I often find myself contemplating the lives of limpets. These perennial residents of rocky coasts inhabit shores that lie between the tides, thriving at this dynamic interface between land and sea. Heavy wave action and prolonged exposure to the air have honed these hardy sea snails to the rigours of one of the most extreme environments on the planet. And despite decades of scientific study the intricacies of their lives are still being uncovered.
Often seen stationary and fixed to one spot, you’d be forgiven for thinking them part of the rock itself. Yet limpets move freely on their muscular foot much like their relatives the garden snail, gliding over the seabed in search of algae, seaweed sporelings and even small barnacles to eat that are scraped and rasped off the rock using their rough tongue–like radula.
Licking rock for a living may seem rather dull but the limpet radula has proved to possess record breaking properties. Researchers from the University of Plymouth recently discovered that the small teeth studding the radula are made of a substance five times stronger than spider silk, in fact it is the strongest biological substance on Earth. The secret to its superior strength lies in the scale of its composite structure. It is made up of a mineral called goethite embedded in a protein matrix that is put together at the nanoscale — that is on the scale of a nanometer which is one billionth of a metre or 10–9 m. Such is the strength of the resulting substance that it rivals even the highest quality man-made carbon fibres. It is truly amazing that on a mostly herbivorous diet and using elements gleaned from the surrounding seawater, they are able to create a material beyond the capabilities of human technology. Their advantage lies in the millions of years of product development and testing that has come with their ancestry.
As well as super-hero teeth they have flawless navigation skills. Following a feeding jaunt, each limpet will return to the very same home position on the rock using invisible trails to navigate. This ability to find their way back ‘home’ continues to puzzle limpet biologists despite decades of study. Experiments have been carried out to try and discern how the homing instinct functions; researchers have set up physical barriers and chemical cordons on rocks to prevent limpets returning to their home positions by the same route as they left. Yet the limpets slowly by-pass any hindrance, proving that not only can they navigate back home, but that they can do so without retracing their original track. You may wonder at the importance of a home patch for a limpet? Well the answer lies in the scar that is carved in the rock by the limpets shell. Like two pieces of a jigsaw puzzle each scar and limpet shell are uniquely paired to each other. The result is a perfect seal between shell and rock that protects the soft tissues from drying out at low tide and makes removal by predators a challenging proposition. Add to this the wide-based, conical shape of the shell and a strong muscular foot and they are well equipped to resist the tug of moving water and pry of hungry predators.
The understated power of these tough little sea snails is something to behold. Though not charismatic in the traditional sense there’s a moral playing out beneath their thick shells that is worthy of meditation. So next time you are on a rocky shore at low tide I invite you to seek out a patch of limpets and sit quietly amongst them. Tune in to their rhythmic rasping of the rock and marvel at how small is truly mighty…