ELKHORN SLOUGH—As Kerstin Wasson stands at the edge of the rising tide lapping gradually higher, her slight frame bubbles with enthusiasm and guarded optimism for the sprawling salt marsh around her.
"It sends shivers up my spine sometimes as I'm walking around these mudflats on Elkhorn Slough holding an oyster in my hands," says Wasson, an adjunct professor of ecology and evolutionary biology at UC Santa Cruz. "There have been humans standing in these places holding oysters in their hands for 7,000 to 8,000 years."
It's true. Wasson and her colleagues know that, millennia ago, Native Americans feasted on the petite Olympia oyster from Elkhorn Slough. The former human residents' trash piles, known as middens to archeologists, are still around today, replete with bits of the faded half dollar-sized shells.
Then, in the 1920s, oyster fishermen from San Francisco Bay trekked down the coast to Elkhorn Slough, located east of Moss Landing. According to the records, they cleaned out the area in a few weeks, harvesting Olympia oysters by the bushel. U.S. Fish and Game biologists surveying the area just a short time later would struggle to find a single oyster. So for decades, it was assumed that the West Coast's only native oyster was gone from the slough for good. But about 10 years ago, a few oysters were discovered here.
When Wasson became research coordinator at the Elkhorn Slough National Estuarine Research Reserve in 2000, the oysters were ideal subjects for the type of conservation research, grounded in ecological theory, that Wasson wanted to develop in her new role. With one foot in academia as a UCSC professor and another in applied restoration and conservation as a member of the reserve staff, Wasson bridges these two worlds, with each benefiting from the close connection.
A bustling harbor nearby, intensive agriculture seemingly surrounding every one of its myriad spindly fingers, and a behemoth power plant looming large at its entrance, the slough is beset by a bevy of human impacts. Like estuaries everywhere, which are "some of the most altered ecosystems on earth," Wasson says, Elkhorn Slough sits surrounded by fertile farmland, near a harbor offering boats protection from the open ocean, and has the relatively still water needed for power plant intake pipes.
But a walk with Wasson and her students makes the recovery of this marshy Eden feel possible. In seemingly every direction, they point out ongoing research intended to increase our knowledge of how the estuarine ecosystem functions, what effects we're having on it as humans, and what can be done to restore the slough to a more natural state.
Preliminary study of the Olympia oyster showed that, while a few were holding on (literally and figuratively) to any hard surface they could find, their numbers were still dangerously low—by Wasson's calculations, only about 500 live in the entire reserve. Even absent the pressure of commercial harvesting, their numbers didn't seem to be rebounding. But things had changed since the days when Native Americans sustainably cultivated the oysters for centuries. The sediment and pollution caused by intensive agriculture and other human activities that have become the norm pose serious problems for filter-feeding oysters.
Operating on the hypothesis that the oysters needed more solid footing, Wasson and her team built oyster reefs, embedding hand-sized native clam shells in one-foot by two-foot block rectangles of concrete. Wasson and newly minted UCSC Ph.D. Rikke Preisler designed these reefs to be "modular and mobile" and placed them at varying depths in the slough.
"It's a general question in conservation biology: If we build it, will they come?" Preisler says.
The hope is they'll learn where best to locate the reefs and more about the effects of pollution, high nutrient loads, and silt on the oysters' recovery, while also accomplishing the conservation goal of doubling the number of oysters in the reserve to 1,000.
A productive partnership
Wasson relishes the relationship with UCSC, because each master's or doctoral thesis adds new pieces to this complex puzzle. "That's the gold standard of understanding ecological processes, having those thorough, in-depth, years of focused study," she adds. "No matter what, we always learn something that ends up being relevant for conservation."
Preisler's doctoral work began at the slough when she noticed how many non-native green crabs had taken up residence. She took on what Wasson calls an "ambitious biogeographic analysis" of the green crab, examining their numbers, not just in the slough and other invaded sites on the West Coast, but also at three sites each in the eastern United States and in the green crab's native Europe. Incidentally, green crabs like to dine on small oysters, so exploring whether an exploding crab population might drag down oyster numbers was an interesting corollary to the abundance issue.
What Preisler found was surprising. While Elkhorn Slough and San Francisco Bay certainly have a lot of green crabs, they were much more abundant on the East Coast and in their native range. And in a later year of her study, Preisler noticed a dip in the population, suggesting that the situation might not be totally out of control.
"This is not to say, well, we have so few, we shouldn't be concerned about them," she warns. But this is the type of work that can be used directly by managers and policy makers, Wasson says. For example, based on this study, they might conclude that it's better to eradicate a species that definitely is causing environmental problems. "This is where the slough is really valuable, because you can think of an interesting project … and you actually have the opportunity to use the reserve to carry out your experiments," Preisler adds. The combination of academics and conservation is, in her words, "a happy marriage."
Save the world with science
With a goal of bolstering shorter-term projects like Preisler's with the long-term data that makes them possible, Elkhorn Slough was one of the first National Estuarine Research Reserves— a network similar to the National Park System, but for estuaries, Wasson says. The National Atmospheric and Oceanic Administration oversees the network, and each reserve is run by a state partner—that's the California Department of Fish and Game at Elkhorn Slough.
Nearly 30 years after the reserve designation, the nonprofit Elkhorn Slough Foundation, which works closely with the reserve, has become the largest landowner in the watershed, and about 90 percent of land that touches the estuary is managed for conservation in some way. Evidence of that focus abounds: Fields up-slope of the slough, owned by the foundation and leased to farmers, boast avocado trees and rosemary bushes, which need less water and fewer fertilizers than crops more typically associated with this region such as strawberries. And 25 water-quality monitoring stations dot the slough and waters nearby, some taking measurements every 15 minutes and transmitting them via satellite to publically accessible web pages.
Data from those stations stretching back 20 years will help Brent Hughes as he begins his doctoral research at UCSC in September. As an ecologist at the reserve for the past two years, he's grown curious about fertilizer runoff from agricultural fields upstream and its influence on the estuarine environment. Hughes explains that the cold water stirred up from the depths of Monterey Canyon offshore, which makes its way into the slough, is brimming with nutrients, with some of the highest naturally occurring nitrate levels in the world.
"That's super nutrient-rich water," Hughes says, and it's the reason Monterey Bay is such a fecund area for plants and wildlife. But those nitrate levels are dwarfed by the ones recorded adjacent to the slough at the old Salinas River channel monitoring station, sometimes 300 to 400 times higher, owing mostly to the massive farms that line the waterway.
But what are the quantifiable consequences to the slough's ecosystem? Hughes will delve into that question in the coming years. He knows more nutrients often translate into burgeoning algal populations. Pointing to sheets of translucent green sea lettuce the size and shape of dinner plates that form thick mats on the water's surface, he explains that out on the coast, this algae is decidedly underachieving, its abundance kept down by competition with more robust species. In the slough, though, it seems to have gone viral.
"Here, maybe it should be an inferior species, but it completely changes the entire system," he adds. At night, the algae suck precious oxygen from the system. When the sea lettuce washes ashore, it putrefies into a gunky mess that fosters the growth of microbes that further deplete oxygen levels and create an inhospitable environment for struggling species like the Olympia oysters.
Hughes plans to track the nutrient inputs that pervade the estuary from their sources by looking at their unique chemical signatures. And he'll survey the multitude of tiny invertebrates that evade the gaze of most visitors but are so critical to its health. He notes the UC Cooperative Extension already works with farmers to find the Goldilocks amount of fertilizer to apply to their crops—enough to make their fields productive, but not so much that it causes environmental problems. Hughes's work could help land managers and farmers further home in on that happy medium.
Wasson sees that drive to see their work applied to a problem in many of the students she advises at the reserve. "There's this excitement about having your research translate to something that affects management on the ground or regional policy," she says.
John C. Cannon is a freelance writer living in Pacific Grove. He is a 2008 graduate of UCSC's science writing program.
