Nature has a surprisingly powerful—yet little-studied—way of keeping the world’s oceans clean and thriving.

By Frank Stephenson

Ask any Floridian about what healthy beaches mean to the state’s economy and get ready for an earful.

If state nicknames made any sense at all, “The Sunshine State” would be called “The Beach State.” Take away half of Florida’s sunny days, and the state’s sandy shoreline would still be a perpetual magnet for people and money year-round—a gritty goldmine that defies every natural force known—from hurricanes to red tide—to keep the state’s tourism-based economy the envy of every landlocked state (and others, too.)

Still, most people don’t have a clue what the real story is behind the value of sandy coastlines—not just in Florida but also around the world. Just in the past 20 years, researchers have begun amassing tantalizing evidence that is revolutionizing scientists’ appreciation of coastal sands and their vital role in the overall health not of seaside economies but of the world’s oceans.

What’s happening is nothing less than a sea change in scientists’ thinking about the vast, sandy bottoms and beaches laid up against the third of the planet that’s dry land. For decades, marine biologists have taught that most of the shallow, near-shore bottoms of the globe’s continental shelf are largely biological wastelands—little more than an immense submarine desert largely devoid of life and of little ecological value. Now, these and a host of other researchers are beginning to realize just how wrong they’ve been all along.

“Sand research”—better known in academic circles as permeable sediment research—is drawing an intriguing new picture of the world’s sandy beaches and shores. Far from being the lifeless, inert byproduct of the sea’s confrontation with land—much less mere scenic backdrops for the most expensive real estate on the planet—these resources are now recognized as living, breathing organisms unto themselves that hold fundamental importance to marine ecosystems the world over.

In the mid-1980s, scientists studying shallow-water marine sediments in Europe were among the first to get a glimpse of these sands’ potential for doing a critically important job—decomposing dead plants and animals. Without a fast, efficient way to digest daily, massive doses of organic matter, the world’s coastal waters would quickly turn into immense, foul-smelling and poisonous cesspools.

Traditionally, the prevailing view among scientists had been that most of this crucial clean-up work was the job of estuaries and salt marshes. Volumes of research papers had been published over the years, describing exactly how these mud-bottomed, inshore systems worked to assimilate a constant flood of organic matter and break it down to its basic elements. Collectively, this colossal, watery compost system was thought to be the primary source for nutrients needed to fertilize the growth of marine micro-plants (phytoplankton), the foundation of a food web essential to no less than 80 percent of the world’s most important fisheries, from clams to grouper.

One of the earliest investigators of the potential that near-shore, highly porous sands have for complementing the decomposition workload of salt marshes and estuaries is Markus Huettel. As a doctoral student at the University of Kiel in Germany, and later in the 1990s as a research scientist at the Max Planck Institute for Marine Microbiology, Huettel’s name appeared on a series of papers describing the surprising capacity of sandy, shallow (30-100 feet) seafloors to clean up the messes left by marine life.

Since then, the study of permeable sediments—sand as opposed to mud—as a major benefactor to the planet’s entire marine biosphere has blossomed. Huettel, now a professor of oceanography at Florida State, is recognized as one of the genuine pioneers of the young field that cuts across disciplines ranging from geology to microbiology.

Primordial Zoo

“When we started this project, I thought ‘wow, what a paradise to work in,’ and it is—when the wind’s blowing. When it stops, it can be a nightmare!”

Joel Kostka is talking about a chief occupational hazard tied to his work with his FSU colleague Huettel, where the two share a “lab” on the eastern end of St. George Island, the longest (at 28 miles) barrier island in the northern Gulf. Long an overlooked, barren stretch of Gulf seafront, the island is now a popular destination for tourists who apparently don’t mind putting up with an assortment of vicious, airborne pests during the warmest months to enjoy the island’s natural charms.

“It gets so bad out here at times, we can’t get any students to come out here with us,” Kostka said. “Sometimes the mosquitoes and no-see-ums (also known locally as ‘flying teeth’—ed.) are just incredible.”

Since 2004, Kostka has braved the bugs to work as a co-investigator with Huettel on the dynamics of the sands flanking both sides of St. George. Supported by the National Science Foundation, the project is designed to get a better understanding of how sandy marine bottoms break down organic material—how fast this process happens and the underlying physics, geology, chemistry and biology involved. For all its progress, sand research still has a long way to go before scientists can draw solid conclusions about how shallow, sandy seafloors fit into the overall picture of marine ecology, Kostka said.

“This kind of in-depth knowledge is crucial if we’re ever going to be able to protect or conserve this resource which we already know is extremely important,” Kostka said. “We believe that what we’re finding right here on St. George can be very useful in explaining how things work elsewhere around the globe.”

Like his friend and colleague Huettel, Kostka is trained in marine microbiology with an academic home in FSU’s oceanography department. Both men bring their own specialties to the St. George project—Huettel has extensive experience in studying the physical forces (e.g. current flow, gravity) that drive water into and through sandy sediments, along with the impact that a variety of bottom-dwelling marine animals have as well, which as it turns out, is considerable.

From stingrays to a variety of submarine worms, literally dozens of species of organisms spend most, if not all, of their lives plowing through or burrowing into the upper layers of sea bottoms searching for food and shelter. Huettel is among the first researchers to document just how important this constant churning activity (known as bioturbation) is to the abilities of sands to decompose organic material.

Although he’s something of an expert on the life history of fiddler crabs—one of the sea’s more ubiquitous foragers and diggers—for his work on St. George, Kostka is primarily focused on far smaller creatures. His primary role is to sort through and identify the main microbial characters living in the sands and figure out what they’re doing there.

It’s a non-trivial task—Kostka estimates that in a single 20 centimeter (nearly eight-inch) core pulled from the field contains upwards of a million species of bacteria alone, much less a complex collection of phytoplankton. But what’s already clear about this microbiotic zoo is that only a few species are the real workhorses in the decomposition game.

Question is, which few?

Wading to Work

It’s a cool (for a North Florida May), breezy morning on the surviving, sea oats-studded dunes of St. George Island. Most of the island’s dunes were flattened by Hurricane Dennis—a Cat 4 storm whose nine-foot tidal surge caught thousands of Big Bend coastal residents by surprise on July 10, 2006.

Markus Huettel and Joel Kostka are arrived at their jumping off point inside the St. George Island State Park. With help from a pair of willing grad students (no bugs today), they lug gear from their van to the surf 150 yards away. At water’s edge, both don “shorties”—abbreviated wet suits—and belts holding up to 60 pounds of lead diver weights. They aren’t about to go diving, but their technique for deploying a dozen measuring devices in the surf zone requires being able to push the instruments into the sand in about five feet of water. Without the lead ballast, the task would be all but impossible.

Already that morning, the team has collected core samples from the bay near where the four-mile-long St. George Island Bridge cinches the island to the mainland. On the Gulf side, not only will they collect core samples, they’ll also switch on the battery-powered instruments—called flux advection chambers—they plant on the bottom and take a series of readings. The morning’s fieldwork takes only three hours, and soon the FSU crew has all gear reloaded into a van and a pick-up, and is headed back to FSU’s marine lab at Turkey Point, about 20 miles east of St. George.

Lab work (both at the marine lab and on central campus) entails a wide range of clever techniques—some of them of the scientists’ own device—to assay the voluminous physical and biological data each trip afield produces. On campus, Kostka oversees a full-scale, microbe-snooping operation set up with the latest genetic analyzing tools. Since it’s all but impossible to pin down the species of a bacterium by looking at it under the microscope, Kostka is forced to rely on a battery of high-tech probes and processes that identify bacteria by their genes. Such “genetic fingerprinting” is the only way to sort through and identify the myriad tribes of bacterial worker-bees present in St. George sands.

Kostka then has to correlate the microbes he identifies with the various decomposition processes, such as oxygen consumption, that he finds going on throughout the cores. Bottom line, for every hour they spend on their favorite island, Kostka and Huettel wind up spending hundreds of hours analyzing samples and poring over the data back in their labs.

“Most of the work that’s been done over the years on marine sediments have been done in muds, and a big reason is because it’s a heck of a lot easier to sample mud than sand,” Kostka said.

Then, too, scientists have assumed that because sand is generally so much cleaner looking than marine muds, it plays only a fraction of the role in marine decomposition compared to darker sediments. Now, scientists know different.

“That’s been a misconception all along,” Kostka said. “There’s a lot of organic matter in sand, but the reason you don’t see it as much as you do in muddier bottoms is because it doesn’t hang around as long. It’s being recycled very quickly, and that’s something we never realized until now.”

Hungry Sands

What intrigues biologists most about the world’s oceans is how and they manage to create life in such incredible numbers and variety.

More than 10 million different plants and animals live in the sea, scientists now estimate. Curiously, at least 30 percent of the food required to sustain this pulsing biomass is produced in narrow, near-shore zones called continental shelves, geological platforms that support the earth’s great landmasses. These approaches to dry land are fairly shallow, and extend from the beach out to around 425 feet, on average. Most estimates put the total area of the world’s seafloors taken up by continental shelves as around 7 percent.

Continental shelves taper off, of course, sometimes sharply, to the world’s deepest holes. But before they fall off into the abyss, these marine plateaus not only serve as the breadbaskets of the sea, producing most of the food needed to support most of the world’s great fisheries, but also offer up vast, buried treasures of oil and gas to industry.

Sand researchers are quick to note that around 70 percent of the world’s continental shelf is covered by sand.

“What we’re finding is that these enormous deposits of shelf sands can be just as effective, and even more so, in degrading organic material as the less-permeable sediments that have been studied so long,” said Huettel. “As a consequence, I believe permeable sands don’t get the consideration they deserve when it comes to setting public policy in managing coastal natural resources.”

Huettel describes continental shelf sands—from the beach outward—as an immense catalytic filter, where oxygen-rich water permeates the bottom and speeds up the decomposition process. Muddy sediments, by contrast, are too fine-grained and too isolated from pounding waves and currents to allow aerated water to have access to organic material to fire up the decay process. In fine-grained muds, decomposition must rely on different physical and biochemical processes for its effectiveness, Huettel said.

In the sands of St. George, both from the bay bottom and the Gulf, Huettel and Kostka have found the highest rates of organic degradation they’ve ever seen.

“I’ve worked in salt marshes for 15 years, off (the coast of) Georgia and overseas as well, and I’ve done work in the Arctic and the deep ocean off Africa,” Kostka said. “I’ve never seen the rates (of decomposition) that we’re measuring in these St. George sediments. It’s truly remarkable.”

Remarkable indeed for a coastline that some oceanographers have described as “zero energy,” a reference to the region’s relatively benign wave action and current strengths. Compared to many places throughout the world—even elsewhere in the Gulf perimeter—Florida’s Big Bend Gulf is indeed a calm sea as a perennial dearth of surfers on its beaches might suggest. Even so, there’s plenty of energy around to drive the most robust, shallow-water decomposition machine Kostka and Huettel have ever studied.

Recycling at Sea

The “machine” reference is apt, given that sandy seabeds have so many moving parts. To the untrained eye, the rippled but otherwise featureless bottoms that run from a typical beach to deeper water offshore appear to be completely inactive. St. George’s sands certainly seem that way, with nothing to relieve a diver’s eyes for miles offshore, in some places.

These seemingly endless drifts of sand may look dormant, but they’re anything but, says Huettel.

“These sands are constantly working as biological filters—we call them biocatalytic filters,” he said. “They never stop working.”

What fuels these immense bio-filters is primarily wave action and current, but that’s just part of the story, he said. As water flows over the top of the sand, some of it inevitably gets pushed downward and into it. This is thanks to tiny but potent differences in water pressure that exist all along the seafloor. These subtle pressure disparities are triggered by any change, however slight, in the bottom’s topography—the height or make-up of the sediment—and commonly, what’s sitting in or on top of it.

As a result, sand begins to arrange itself into undulating patterns of ripples, with orderly crests and troughs. Like air rushing over the wing of an aircraft, currents flowing over these ridges generate a low-pressure zone over each ripple crest, drawing water upward from the sand. Corresponding high-pressure zones develop in the ripple slopes and troughs force water back into the sediment.

It’s this push/pull action—kept in perpetual motion by flowing water—that’s the key to how the filter works. Organic-rich water gets pulled down into the biological processing factory where bacteria rapidly strip everything down to its basic ingredients. What the bacteria don’t use for their own growth gets flushed back into the water column as raw minerals, nutrients and gases—primarily nitrogen and carbon dioxide—completing a key role in the sea’s recycling of matter.

Huettel says the system doesn’t necessarily need strong currents to work. In fact, on St. George he’s documented that the sand filtration system can work just fine even when the current flow is so small that only his sensitive instruments can detect it.

Of course, stronger currents can force water deeper into the bottom, particularly when currents encounter a stationary object.

“Even a crab sitting on the sand can have an effect on how much water gets pushed downward at a particular spot.”

Animated Sandbox

Sand researchers have a special term for the water that gets entrained in sediments. It’s called pore water, a reference to the pores that exist between individual grains of sand. his is where water collects and also where it gets introduced to the microbiotic zoo referred to earlier. More than 90 percent of the bacteria that live in the top layers of most permeable sediments are stuck to sand grains, Huettel said.

Even before dead and dying organic material settles out onto the bottom, it’s being literally torn apart by a combination of wave action, currents and a host of hungry organisms ranging from bacteria to sharks. Eventually, such material is reduced to bits and pieces small enough to be absorbed into the sand bed where it becomes food for the horde of microbes Kostka hunts for.

Most of these bacteria are the same species that live in mud, Kostka said. The critical difference is that because sand is so porous as compared to mud, there’s a great deal of mixing going on that constantly brings fresh organic material into contact with decomposing organisms. This mixing is a combination of both the push/pull of pore water—which also exists in mud but doesn’t circulate—and the aforementioned bioturbation—the incessant digging, burrowing and foraging habits of dozens of animals.

Among the busiest and most noticeable of these are shrimp, crabs, sand dollars, starfish, snails, and bottom-hugging fish such as flounder and rays. Even marine plants help by injecting oxygen directly into sand via their roots, Kostka said.

The impact that all these larger organisms have on submarine sands is akin to what goes on at a well-kept golf course, he said. Greens keepers routinely run over their courses with heavy machines that punch holes into the soil to keep it aerated and healthy for grass.

“This is the same principle on the seabed,” said Kostka. “All these larger organisms are aerating the sands, which stimulates the microorganisms to cycle nutrients faster.”

Even animals that don’t move around much—such as clams, oysters, mussels and other bivalves—constantly pump water into the sand as they feed. Both the bay and the Gulf side of St. George Island are home to dozens of species of such sedentary mollusks, along with an assortment of marine worms that permeate the seabed in huge numbers.

New Respect for an Old Resource?

Anyone who’s ever lived on or near a Gulf beach for any length of time can vouch for the power of nature to make some of the foulest messes ever to draw flies.

Every year, some worse than others, mountains of dead seaweed pile up in reeking windrows on beaches from Key West to Veracruz where they fester in the sun like ripe, gigantic corpses. Sweetening the stench are countless microscopic plants and animals that ride to their deaths on the stuff. The combination can be a tourist repellant more potent that a shark attack.

Periodic outbreaks of red tide—caused by population explosions of a few nasty species of marine algae—also add to the misery by casting untold tons of poisoned victims—both fish and other marine life—onto Gulf beaches each year.

Most beachgoers give little thought to how this annual toxic bouillabaisse gets cleaned up. The stuff that gets loaded onto dump trucks for a trip to the closest landfill is a trifle compared to what nature takes care of, quickly and free. Florida’s tourism industry has a vast, sandy bio-filter surrounding the entire state largely to thank for that.

“These sands are critically important in digesting all this stuff,” Huettel said. “And of course it’s not just the stuff that nature produces. These filters have to deal with all the pollutants pouring into the seas from what we’re doing on land. And like any other filter, this biocatalytic filter has limits in what it can handle.”

While all the filtering and buffering work of salt marshes and estuaries remain absolutely essential in keeping the worst of humanity’s assaults on the world’s marine environments in check, Huettel and Kostka say the kind of research they’re doing shows that permeable marine sands can play a big part in that. They’re confident that some day, this emerging new field of marine science will prove the value of an immense resource that so far still doesn’t get the respect it deserves from scientists and environmentalists.

“People tend to overlook the sands,” Kostka said. “They still get called ‘undersea deserts’ and things like that, and that’s unfortunate because these sediments teem with life and do extremely important work.

“But it’s true that there’s just not much known about these resources yet. We’re out to change all that.”