The surprising science behind beach ecosystems

canoes-cottage-beach Photo by Alessandro Cancian/Shutterstock

Unlike the cottagers who sprawl on its surface, inert as barnacles and happy as clams, a beach is eternally restless. While it may look like the same sandy spot where you flaked and baked last summer, it is ever-changing. Today’s beach is not yesterday’s or tomorrow’s. This magical strip between water and land is one of the most dynamic environments on the planet, endlessly reinventing itself. Whether coastal or inland, freshwater or salt, your beach is the ultimate shape-shifter.

What makes it so changeable? Waves and wind are the driving duo. Waves are most key, as they actually move beaches around, restyling them, stripping them, widening them (from front to back—that is, from water’s edge to inland vegetation). But you’ve got to have wind to generate those waves, and you’ve got to have “fetch,” the distance a wind travels over water, says Robin Davidson-Arnott, a coastal geomorphologist and professor emeritus in the University of Guelph’s geography department. “You need a fetch of at least 80 to 100 km to create waves big enough to produce a fairly wide beach.”

So, the smaller the lake, the shorter its fetch, the weaker its waves, and the dinkier its beaches. But that doesn’t mean they aren’t dynamic. “There are high-energy beaches and low-energy beaches,” explains Bernard Bauer, a professor of earth and environmental sciences and geography at the University of British Columbia. Generally speaking, a Pacific Ocean beach, with a fetch all the way from Japan, is super high energy and an Atlantic Ocean beach not so much, thanks to west-to-east-moving winds called “westerlies,” which drive waves straight to Pacific shores, but are typically directed offshore on the Atlantic coast. Great Lakes beaches are less energetic than Atlantic ones, and so on. Geography factors in too: a beach on an open, unsheltered coast is more energetic than a “pocket” beach protected by two headlands. And finally down to the wee crescent of sand on a little inland lake, which may look static to you but is still in the game. “Beaches are always moving,” says Bauer. “Even piddly waves are moving tiny amounts of grain.”

Wind moves sand too, lifting and carrying it up the beach, where it gets trapped in vegetation and builds dunes over time. (Beaches too narrow to allow this “aeolian transport” are duneless; you need at least a 10-metre stretch for wind to blow across and scoop up sand.) Dunes act as sand reservoirs for beach repair. “When a big storm surges up, it carries dune sand back to the beach,” says Davidson-Arnott. “And if it’s a very big storm, waves will carry sand back to the water, where it collects in sandbars.” When the weather calms, gentler waves return sand to the beach, and the wind returns dry sand to the dunes. It’s a vibrant cycle of destruction and renewal—erosion is natural to a beach, and usually temporary (unless we interfere).

A beach can also lose its sand, but gain another’s, as more forces come into play. Longshore currents, generated by waves hitting the shore at an angle, run parallel to beaches, stealing sand from one place and depositing it downshore. This longshore “drift” of sediment sometimes accumulates into sandspits, which project into the water and can achieve some doozy lengths. At 40 km, Lake Erie’s Long Point is the biggest sandpit in the country, far larger than any on our ocean coasts.

Long-Point-Lake-Erie-Ontario Canada
Long Point peninsula view of the point with the lighthouse, Lake Erie Ontario Canada. Photo by SF photo/Shutterstock

Of course, Pacific and Atlantic beaches boast serious tides (and while we’re one-upping ourselves, the Bay of Fundy, on the east coast, has the highest tides in the world, at 16 metres). Fundy aside, because tides rise and fall so gradually, most don’t push a lot of sand around, but, says Bauer, if you get a storm on top of high tide, the water will reach a much higher point on the beach, with potentially more erosion and flooding. “The tide says where the wave action is going to be focused on a beach.” On coastal and inland lakes, the tide hasn’t got much to say at all; though a tidal force does exist, it is almost imperceptible.

These various movers and shapers change beaches, but they don’t create them. You need the material to be there in the first place. Over millennia, rock is broken down into little bits of mineral, which are delivered to the shore by rivers or eroding glacial deposits, such as moraines and cliffs. This keeps the beach fed with a steady supply of sediment. (Lake Erie’s plethora of eroding sand bluffs is a key reason why Long Point got— and stays—so long.) No beach’s sand blend is the same as the next—the grain size, colour, and composition are as unique as a thumbprint, mirroring the beach’s local geography. Little wonder there’s an International Sand Collectors Society, whose members call themselves “psammophiles,” or lovers of sand.

Some minerals endure eons of wear better than others— the stablest are quartz and feldspar, which dominate in beaches across the country and give their sand a whitish-grey tone. Occasionally mixed in is black magnetite, very attractive to junior scientists who think to bring a magnet to the beach. Black sand also colours some B.C. coasts in the form of leftover volcanic basalt. Maritime cottagers walk on shores glittering red with eroded sandstone, which is quartz coated with iron oxide. (After a few years of being scoured by waves, the coating can wear off and the sand turns white.) And many beaches get their sparkle from black and white mica, its flat flakes reflecting sunlight. Along with these mineral grains, which can be hundreds of millions of years old, sand has more newly arrived constituents, such as ground-up shells, only a few years old, or bits of invertebrates that washed up today. All this is under your beach towel. If you weren’t a psammophile before, are you now?

Which brings us to the non-human lovers of beaches, the plants and creatures that make this tough and transient place their home. “A beach is a very extreme environment,” says Judith Jones, a biologist with Winter Spider Eco-Consulting, on Ontario’s Manitoulin Island. “It’s hot, dry, and has high levels of light. Things blow around, and things get sandblasted.” Yet amazing survivors abound. Dune grasses, such as marram, suck silica from the sand, armouring their leaves against grit abrasion, lack of water, and broiling hot temperatures (40°C–50°C) in dune hollows. Growing about a metre tall, the grasses trap the sand that builds the dune. A vast, deep network of roots anchors the marram against high winds and stabilizes the dune like rebar in a building. Once steadied, the dune is more liveable for other vegetation, such as wormwood and Pitcher’s thistle. “Like many beach plants, they are grey-green in colour because their leaves are covered with a layer of tiny white hairs,” says Jones. “This helps to guard against drying out and sandblasting.” Others have long taproots that pull up moisture and help them hang tight in shifting sand.

If there’s a wetland behind a dune, some turtle species will breed, then come to the beach to lay ’em and leave ’em, letting the warm sand incubate their eggs. The piping plover, an endangered shorebird, often nests where the beach meets the foredune (the first dune facing the water), so that it’s sheltered on one side but can scan the shore for predators. One tiny hunter, the tiger beetle, hides as a larva in sandy hollows, lying in wait 2 PM to chomp on passing ants and spiders. As an adult, it sprints across the beach, chasing its prey, which might seek refuge under the “wrack line”—the scraggly, smelly strand of seaweed, dead bugs, and other flotsam that lies between a beach’s foreshore (the wet part) and backshore (the dry part, except when submerged by storm waves). The wrack line looks like something the waves dragged in—and it is—but to plovers, tiny crustaceans such as sand fleas, and amphibians such as the Fowler’s toad, it’s an all-you-can-eat buffet. Every niche on a beach is alive.

By now it should be clear that this is an awesomely active ecosystem, not a sandbox. Perpetually in motion, eternally adapting, it grows, it shrinks, it hurts, it heals, it exposes, it shelters, it shape-shifts. But for all this dynamism, it’s also a place of dreamy idleness, where cottagers can kick back, maybe read a story about beaches, and contemplate infinity in a grain of sand.

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