Observing the Beautiful, Secret Lives of Sandhoppers
Adam Nicolson on an Overlooked Beach-Dweller
A bank of rolled and broken seaweed gathers at the head of the beach after storms where it lies for weeks in long dark bolsters. In the summer it can grow crusty on top, dried by sun and wind, with bits of driftwood and plastic caught in it, and the weed itself turning a mottled ochre, the colors of a fire that has burned down. But even then when you lift away its upper layers, something else appears, the semi-liquid slutch of rubbish and rot, every surface slimed, not the bright firm beauty of the sea itself but a world thick with decay, the microbial tide surging through the tissues of the weed.
Put your fingers in amongst its slipperiness and you can feel the nutrients being released back into circulation, no longer shut into their organisms but ready for another turn. It is the gift from the sea, delivered not by the beneficence of summer but by winter storms that have torn the wrack from the seabed and brought it ashore.
I begin now to poke into the mounds of weed. It is March, a cold dampish day with spits of rain hanging in the wind. The air between here and Rubha an t-Sasunnaich has thickened into a mist. The waterfalls are running but I cannot hear them for the gale. The grass is dead and brown and there is scarcely a sign of spring. It is the end of winter, everything reduced and bitten down, shut like a filing-cabinet drawer. The whole place feels bleached.
The tides have been up over the grass. All kinds of things are mixed in with the wrack: limpet shells, emptied of their inhabitants, upside down cupping the rain. There is most of a tree in here, an ash, its bark chewed by the deer, whose teeth have scraped furrows into the wood beneath. A huge grey buoy, torn away from a fish farm, is half-buried in the wrack. The carapace of a green shore crab has the double puncture of an otter’s canines crunched into the lid as if through a water biscuit. There is a hazelnut here, still whole, but when I bite into its shell, the taste is of salt and rot. The sea has got in and the nut is pulp.
The oystercatchers and sandpipers are spending their day picking through the weed like shoppers in a market turning over the clothes for a bargain. There are opportunities to be had. Come closer—it is the governing instruction of life on the bay—and the rotting weed shows it is more full of life per square inch than anywhere on this late winter shore. Sink your hands into the slime and slither-gloop of the disintegrating mass and feel your way towards the creatures that make this place their home. There is a mass of them—millipedes and wrack-fleas—but what literally jumps out are the jumpers, the sandhoppers, the tiny crustaceans no bigger than the paring of a thumbnail that love the rotting weed.
I have seen them a thousand times before and never considered their existence, never named them, never caught one, never looked at one, never thought what they might be beyond something like the energy of rot, bursting up out of the sludge of disintegration. Now, though, the invitation takes me in.
There are two kinds of sandhopper on Scottish beaches. One is pale brownish called Talitrus saltator, the “leaping knuckle jumper”—talus is Latin for a knuckle, talitrus for a finger-flick—which spends the day buried in the sand and emerges at night to feed on patches of wrack. The other, with which I am more familiar, is pinkish and called Orchestia gammarellus, the “little shrimp-like dancer,” named after the troupes in ancient Greece who performed on the dance floor, the orchēstra, where the tragedies would also be played. Orchestia lives all the time in the wrack.
Both Talitrus and Orchestia are amphipods—the name means that they have several different kinds of feet—and every time you open up their world-in-dissolution, they go through the same wonderful three-part routine: leap; wriggle; play dead. Put the weed lid back on, lift it again and they do it again: leap, wriggle, play dead, finally curling up into self-protective balls in the shadows of the wrack.
Eighteenth-century naturalists had looked at them, often thinking they were a version of woodlice, but the first person to examine them carefully was one of the heroes of the shore, Colonel George Montagu (1753–1815), scholar-soldier, veteran of the American War of Independence, founding fellow of the Linnean Society, pioneering ornithologist, conchologist and mammalogist before any of those terms had been invented. He ran off with a niece of Lord Bute when he was twenty, but became bored by her grandeur and, after beginning as a pursuer of game, increasingly turned to the study of nature.
In 1798, with his mistress, the Danish beauty Eliza Dorville, he abandoned his life and wife to set up with Eliza near Kingsbridge in Devon. Society was outraged. Montagu was disinherited by his family, court-martialled for creating a bad example and so turned with exquisite patience and assiduity to the creatures of the natural world. It was a model for shore-life: ignore society; attend to this.
Montagu spent his days poking about in the waters of Salcombe Harbour, naming species after species for the first time (including a hundred new molluscs), acquiring a Montagu’s blenny, Montagu’s harrier, Montagu’s ray, Montagu’s sucker (a kind of fish) and Montagu’s sea snail. Eliza provided him with a stream of children—the two never married—and made the calm and refined drawings that illustrate his books of birds and shells.
Under these happy and freethinking hands, the sandhopper entered the annals of science. Having watched “the multitudes which are seen skipping about in all directions upon our sandy beaches in a summer evening,” Montagu looked patiently and admiringly at the little creatures. He was one of the first British naturalists to examine both preserved specimens and the living animal, and to make regular use of a microscope.
Through his eyepiece Montagu saw that the sandhopper was “oblong, sub-compressed, smooth, and extremely glossy. [Its] colour when alive corneous; when dried it becomes paler, and by exposure to the sun gains a tinge of pink; and the antennae partake of orange yellow. It is frequently found on the seashores bleached white.” They lived in vast abundance “burrowing under the various rejectamenta of the sea, devouring both animal and vegetable matter with great avidity.”
If you can catch one of these mistresses of the rejectamenta and hold it by its legs, it does not, to be honest, look like an efficient design. A woodlouse and other isopods (which have, by contrast with the amphipods, only one kind of leg the length of their body) are compressed vertically, so that their bodies are low, wide and stable. These amphipods are compressed laterally, so that they are tall for their width, with the same proportions as the trolleys that cabin crew push up and down the aisles of aeroplanes. You might think if you set an Orchestia on its feet, the high center of gravity would mean it falls over. In fact it doesn’t, and stabilizes itself by spreading its legs wide, like the legs of a camera tripod. Why the lateral compression?
When either the Orchestia or the Talitrus is disturbed, all the animals that have been exposed start to jump at random, scattering as chaotically as the bubbles above a newly poured glass of champagne. Prey animals of all kinds do this, zigzagging, spinning, looping or bouncing away from the predator in what biologists have called “protean flight,” a storm of signals to confuse the killer, encouraging it to follow one then another and so allowing all the potential victims to escape. Mice, spiders, squid, fish and broods of young songbirds often “explode” like this when an intruder threatens. If a single goal is sought, the offering of multiple options encourages indecision. Sandhoppers’ genes have learned to overwhelm the processing capabilities of their predators.
The Soviet marine scientist A. I. Bulycheva very carefully watched an Orchestia hopping. She thought that it balances on a pair of legs in the middle of its body, draws its whole self tightly together so that its tail and enormously powerful back legs—they look under the microscope like the hams of a linebacker—are pressing into the sand, and then suddenly flexes its thorax so that it flings itself into the air, with no control over the direction it takes. The movement is astonishingly quick and effective. If you sit and watch them in flight, the impression is that each small animal is in one place at one moment and another a second later, with no catchable transition between the two, animal-quarks living in a strange quantum-crustacean universe.
Those back legs act as shock absorbers when it lands (or so Dr. Bulycheva says, even though they seem usually to land on their sides to me). Meanwhile Dr. G. Bracht from the University of Münster has filmed the whole performance (at 1,000 frames a second) and found that an Orchestia’s escape-jump lasts on average between a third and half a second, can cover a distance of eighteen centimeters and achieves an average acceleration on take-off of 300 meters per second per second. Within that time frame, Orchestia usually makes between four and six somersaults.They must be making decisions. They must have minds at work.
Be amazed. It is the fizz of life itself, the sand-jumpers and weed-dancers springing into spectacular rocket-fueled survival. As they jump, the huge, supervising presence of the oystercatcher or sandpiper is confused. The final landing is a moment of vulnerability, when the predator can reorientate and find its prey, but the amphipod does not stand to be available once again to the hungry bird. It begins to wriggle on its side, like a rugby player caught in a tackle, all nine pairs of legs hard at work pushing the animal forwards and sideways down in between the crevices of the rotting weed. No woodlouse or leg-based isopod could do such a thing, or at least so easily.
The amphipod slithers towards safety, entirely capable on its side, and with its relatively soft and shiny cuticle, far more pliable than the shells of the marine crustaceans, the shrimps and prawns, from which it is descended. The calcium carbonate that stiffens and hardens the shells of those sea creatures is not present in the exoskeleton of these weed-dwellers. They choose escape over armor. A lighter shell makes them sprightlier for jumping and also makes them supple, so that they can slip and wriggle away into the protection of the gaps between the rotting weeds. Hence the lateral compression.
Once there, they fake death, curled up into a seed-like ball whose sheer immobility is its camouflage. If you did not know they were there, you would not find them in the shadows and crevices of the weed. But poke about among these living dead and they will, quite literally, spring to life again, running through the gamut of their evasions.
Most of the nearly 10,000 amphipod species live in the sea, and these beach-dwellers are the descendants of marine ancestors that have come to an enriched but more difficult world, one in which flux both provides the basis for life and is its enemy. Bundled-up wrack is delicious for them but the temperature rises and sinks to greater extremes on land than in water, even inside the mounds of weed, and so desiccation, by definition impossible in water, becomes a constant threat. It is something life itself, the body itself, must defend against. That is one purpose of the semi-pliable, near-crunchy shell of these amphipods; if an Orchestia loses more than 25 percent of its body-water, it will die.
They do their best to avoid such a fate. Orchestia has a system of pores in its protective shell. A layer of wax is secreted through them, waterproofing the shell, making it like the waxed cardboard in which the fruit and vegetables of organic box schemes are delivered. The wax will keep the Orchestias damp inside. It has a melting point of about 37 degrees Celsius, which means the sandhoppers cannot go wandering about with any safety in full summer sunshine. If they did, their protective coat would melt and they would die of dehydration.
Large-scale catastrophe can strike. One very warm May, when sunshine hung over the West Highlands of Scotland for two full weeks, the weed on the beach dried to the consistency of dark, wrinkled, uncooked pasta, not only in the upper layers but deep down into the bulk of it. I went looking for the Orchestias and lifting the weed away in stiff plaques found crowds and crowds of them lying there on the gravelly sand, dead and pink as if they were a plateful of cooked shrimps, the victims of drought and unseasonable early summer warmth.
Normally, though, the wet weed is both hiding place and restaurant. If you remove the top layer of weed, but shade the Orchestias as deeply as you can, they feel they might still be in something like the dark and they begin again to lead the normal hidden life of the cryptozoic. They feed, nibbling on the weeds, and from time to time they also start to look after themselves, their little hands and feet feeling over the surface of their own shell-coat for any grains or fragments that might be abrading it, breaking the glossy seal that Colonel Montagu noticed and so putting them in danger of drying out. Orchestia must groom to stay alive, in particular picking anything out of the joints in their legs where a speck of dust or sand could damage the connecting membranes and allow the precious wetness of what biologists call “the internal milieu” to escape.
To sit and watch them about their business, their multiple limbs flickering and pausing over their own bodies, keeping house, keeping themselves proper, ensuring their own continuity, is a challenge to any pre-existing idea of animal consciousness. They must know and feel where there is a speck of grit to be removed. They must know how to use the multiple tools of their various limbs in a way as effective and as complex as a multibladed penknife. They must be making decisions. They must have minds at work.
Excerpted from Life Between the Tides by Adam Nicolson. Published by Farrar, Straus and Giroux. Copyright © 2021 by Adam Nicolson. All rights reserved.