THE CLAM BEFORE THE STORM
Researchers try to control a small clam with an extreme knack for reproducing in Lake Whatcom, Washington.
Story by Emily Dietzel | Photos by Nick Pinkham
It’s mid-April when Teagan Ward wades out into the frigid water of Lake Whatcom in her rubber thigh-high waders, armed with a dented spaghetti strainer and a bright-pink hula-hoop. Broken shells litter the shore of Bloedel Donovan Park, definitive evidence of her target’s presence. Ward and her team are on the hunt. Floating hula-hoops on the water mark areas to be searched, and the team shovels up chunks of sediment, sieving it through the strainers in search of their target. The first attempt yields only large pebbles and halved shells, but as the team probes deeper they find them: small, yellow-brown clams no larger than a quarter.
AT FIRST GLANCE, the Asiatic clam, Corbicula fluminea, seems harmless. It appears much like any other native mollusk, but its miniature size and raised, curved ridges give it away to the experienced eye. But for this clam, it truly is what’s on the inside that counts — reproductive versatility.
First recorded in the U.S. 80 years ago, these tiny clams have since made a big footprint. Teagan Ward, the aquatic invasive species program coordinator for the city of Bellingham, is working to protect the local community from these seemingly harmless creatures. The species is a harbinger for ecological change in freshwater ecosystems. It forces out native species, degrades water quality, and lays the groundwork for invasion by more overtly threatening organisms. Since 2011, the Asiatic clam has established a growing population in Lake Whatcom, Bellingham’s primary watershed.
Most clam species have the characteristics of only one gender and release clouds of eggs or sperm into the water to combine by chance. The Asiatic clam, however, does not rely on fate alone. As a hermaphrodite, the Asiatic clam possesses the sexual traits of both males and females. This means it can reproduce sexually, like most other clams, or asexually, using only its own genes to create offspring. The Asiatic clam may even opt to clone itself, creating identical copies of itself within its body. The parent protects the babies until they form small, soft shells and sticky bodies, perfect for hitching a ride on rubber boots, Frisbees and fishing boats, into uncontaminated lakes for colonization. With more reproductive options than all other species of freshwater bivalve, these clams are strategic reproducers. Living up to four years, each clam is capable of producing 68,000 offspring every year.
Over the last century, the clam has dominated many continents, even reaching the top 100 Worst Invasive Species List in Europe. It was first noted in North America in 1938, and established itself in Lake Washington ten years later. Today, the shores of Lake Washington are littered with the clams.
“At times you’ll think you’re walking on gravel, and you’re actually walking on clams,” said Leo Bodensteiner, an aquatic ecologist and professor of environmental science at Western Washington University.
Upon its discovery in Lake Whatcom, it made the city of Bellingham’s Most Unwanted Invasive Species List.
This rapid reproducer is already changing the drinking water of about 100,000 people in Whatcom County. The Asiatic clam alters environments simply by eating and reproducing profusely. As a filter feeder, it sucks nutrients from water and sediment. The clams also take oxygen directly from the sediment and out of reach of native species.
The biomass of phytoplankton and zooplankton can decrease by up to 70 percent, because they are all the clam eats, according to a 2013 study by researchers at the University of Namur in Belgium. Ordinarily, plankton serve as the main food source for many native aquatic species, but because of Asiatic clams’ sheer numbers, they hog all of the lake’s resources. Like a tired toddler, these clams do not share well, and native species are paying the price. They suffocate and starve while the clams feast.
“Let’s say you love to go out on the lake and catch some fish out there. That fish is probably gonna be smaller and less abundant after Corbicula has moved throughout the lake,” said Jason Buehler, author of the most recent study on Lake Whatcom’s Asiatic clam population. “In the end there’s only so much energy in that ecosystem, and it mostly goes to these clams.”
Back at Lake Whatcom, metal strainer in hand, Ward set to work digging in various locations to find them. Venturing deeper into the lake until the water lapped at the top of her boots, she searched the murky sediment. But without the help of shovels, scuba gear, hula-hoops and ideal temperatures, her efforts were fruitless.
An environmental engineer by trade, Steve Hood has an intimate familiarity with the species, and suggested Ward’s search would produce better results in the winter when the lake is low.
When the clams were first discovered in Lake Whatcom, Hood was on the scene, and his curiosity compelled him to taste them.
“I love seafood, so I thought, ‘Oh, well fresh water seafood? Let’s give it a try,’” Hood said. He enjoyed the experience enough that he recommends it to others. Hood offered local clambakes as an unorthodox solution to rising Asiatic clam populations.
Since their arrival, local government agencies have been working to contain the spread of Asiatic clams, but management options are limited. No targeted pesticides exist to easily eradicate them, Bodensteiner said. Even if they did, the nature of these clams pose a unique challenge.
“They can clam up,” he said — no pun reflected in his tone, but surely intended. “They don’t need to take in any water, in some cases for upwards of three days, maybe longer.”
He said for this reason, any poisons used to remove the clams would have to stay in the water until they open up again.
Ward studies the efforts of other programs managing the species to learn the best way to respond to their presence. In New York state, the managers of Lake George have attempted an alternative to poisoning the clams called benthic mats, she said.
“They put these mats down you know, at the bottom of the lake, and the goal there is to completely suffocate the clams,” Ward said. “The challenge with that is it’s very costly for one, and secondly, it kills a lot of other species as well… Eradication is not really an option.”
Instead, Bellingham’s Aquatic Invasive Species Program focuses on containment. The species likely reached the lake through a contaminated vessel, as specimens were first found near a boat launch site, Ward said. They developed a boat monitoring system which became mandatory in 2014. Last year, her team conducted more than 12,000 inspections between Lake Whatcom and Lake Samish, with 60 percent of them taking place at Bloedel Donovan Park.
“We have a total crew of 16 inspectors across the two lakes, working at four check stations,” Ward said. “We’ll be here from dawn to dusk, seven days a week until the end of September.”
As she spoke, a bright-red fishing boat was undergoing inspection. The owner answered questions regarding where and when the boat was last launched, while inspectors searched the vessel for any signs of mud or stagnant water, which could transport larval clams.
However, some believe the program may not be doing enough to prevent the spread of this invasive species to unaffected lakes.
“There’s about a 70 percent compliance rate,” said Karlee Deatherage, the clean water policy analyst at RE Sources for Sustainable Communities, a Bellingham-based environmental group. “We do have some grave concerns about the lack of enforcement that happens during the peak boating season… It’s such a huge loophole.”
Ward argues compliance rates actually range from 85 to 90 percent, and are rising every year as a result of educational efforts. Her program runs an online aquatic invasive species course which lowers boat permitting costs, incentivizing people to learn about the ecosystems they engage with. But with invasive species, even a one percent non-compliance rate may be enough for them to spread.
“More enforcement would probably help, but our job is always education first,” Ward said. “Most people, when they understand why we’re doing this, they’re on board, and we take steps to make it easy for them.”
Asiatic clams are not the only species threatening local drinking water. Many consider them a warning sign for two more dangerous mollusks — zebra and quagga mussels. The mussels invade in the same way as the clams, via mud or water on contaminated surfaces. These mussels can attach to hard surfaces, creating the potential to clog water pipes. If these species reach lake Whatcom, they could block Bellingham’s water supply and cost thousands of dollars in repairs. Fortunately, they are not in Washington yet, but were spotted in Montana in late 2016.
Ultimately, the community plays a large part keeping these invasive species under control.
“There are still things that we can’t go back from, and despite all the technology and all the money we have, there’s no way to stop these things once they’re introduced,” Buehler said. “Once these invasives are in your favorite lake, they’re there forever.”
