The sweet potatoes in this pie originated in the New World. Photo: paul goyette.

As you fill your grocery cart with food for Thanksgiving, pause for a minute and think about where that food came from. I don’t mean is it local or organic or hormone/pesticide /gluten-free—I mean is it Old World or New World? On what continent did that food evolve?

During the age of exploration, Europe was called the Old World, along with its continental neighbors in the Eastern Hemisphere, Africa and Asia. The Americas, North and South, were the New World. Australia is sometimes lumped with the New World, too. This is a geographical and historical division. But the Old World/New World distinction also speaks to the biology of the regions. Organisms that originated on one continent are different from those that evolved halfway around the world. And for the most part, living things—animals, plants, microbes—didn’t travel from one hemisphere to the other without human help.

The sweet potato/yam mash-up is my favorite example of an Old World/New World confusion. Sweet potatoes originated in Central or South America, and are the starch-filled roots of plants related to morning glories. Yams, however, are completely different. They originated in Africa, and are actually the stem tissue of a monocot plant. Most of what we see labeled as “yams” in our grocery stores are actually sweet potatoes. The common name confusion started centuries ago, when African slaves brought the name—but not the vegetable—to the Americas with them. Yams don’t grow in temperate North America; they need a tropical climate, like Africa, Asia, or the Caribbean (where they’ve been imported).

So let’s go through your grocery cart. Your soon-to-be-mashed potatoes? New World—they originated in South America. (And the Irish Potato Famine occurred long after potatoes were imported to Europe.) The corn in your cornmeal stuffing originated in the New World, too. Your turkey is from the New World, but the soy in your tofurkey is native to Asia. And the apple in your apple pie is not at all American—it originated in Europe.

Many foods have moved across the ocean. This mixing of culinary components and cultures is definitely something to be thankful for. (Invasive plants and animals—and diseases—that have crisscrossed continents are something else entirely.) This Thanksgiving weekend, I plan to read the book 1493: Uncovering the New World Columbus Created. Author Charles C. Mann writes about the Columbian Exchange—the movement of plants, animals, and people from one hemisphere to the other. I’ll read it while enjoying a cup of coffee (Old World—Africa) and some leftover pecan pie (New World—North America).

"Attack of the Alien Invaders," produced by WVIZ/PBS, was first created as an educational series called "LSI: Life Science Investigation."

Lake Erie is considered to be the most productive of all five of the Great Lakes.Within its waters are diverse and interdependent plants and animals that make up an intricate web of life. Mostly due to human carelessness, the lake has become home to an increasing number of non-native plants, animals, and micro-organisms which threaten the balance of the entire ecosystem.

In the WVIZ/PBS program, Attack of the Alien Invaders, Dante Centuori, Director of Creative Productions at the Great Lakes Science Center in Cleveland, Ohio, traveled in and around Lake Erie visiting with scientists and government officials who are investigating Lake Erie’s ecosystem, the challenges it has faced in the past, as well as those it may face in the future. Of particular interest was one of the biggest potential threats to the lake- a voracious invasive species collectively called “Asian carp.”

Bighead carp (Hypophthalmichthys nobilis) and Silver carp (Hypophthalmichthys molitrix) were first introduced to the U.S. in the 1970s as a chemical-free and “environmentally friendly” way of cleaning up algae in southern fish farms and water treatment plants. During the Mississippi River floods of the early 1990s, these fish escaped into “The Big River” and its tributaries. Since then, these big, hungry, and prolific fish have made their way north all the way up to the back door of the Great Lakes. If they enter the Great Lakes, it is feared that these fish will continue on to Lake Erie where they could further disrupt the Great Lakes’ most productive ecosystem, with unknown long-term consequences.

John Hageman from Ohio State's Stone Laboratory shows Dante Centuori an invasive Silver Carp.

Dante first visited Stone Laboratory, a research facility located in the Western Basin of Lake Erie in Put-in-Bay, Ohio. There, he met John Hageman who displayed, and dissected a Silver carp; revealing an anatomical structure that makes these fish particularly threatening to the food energy balance so important to Lake Erie’s native inhabitants. Dante then accompanied another Stone Lab researcher on a good old fashioned Lake Erie “fish trawl” where he came across many of the lake’s native and invasive species– such as the omnipresent zebra mussel and the abundant quagga mussel, two detrimental invasives brought in to the Great Lakes by the ballast water of ocean-going vessels.

Dante continued on to Old Woman Creek, a national research center and fresh water estuary in nearby Huron, Ohio, where he encountered some frisky common carp (Cyprinus carpio) whose behavior may help scientists predict what may happen to Ohio’s interior rivers and streams, if their distant relatives from the east choose to join them. Next, he returned to Stone Lab to investigate how the Bighead and Silver carp have influenced and impacted the native species of the Mississippi and Illinois River ecosystems. He next traveled to Lake Erie’s Central Basin- to Cleveland, Ohio for a rendezvous with a federal employee who explained how Asian carp are being monitored and controlled in one of the most probable points of entry into the Great Lakes, Chicago’s Shipping and Sanitary Canal at the southern end of Lake Michigan.

Lastly, Dante returned to Put-In-Bay where he talked with Jeff Tyson of the Ohio Department of Natural Resources, who described the management techniques used to control one of the harmful invasive species in Lake Erie; the Sea Lamprey. Could techniques similar to those used to control the Lamprey be applied in the event of an Asian carp invasion? What other plans are in place if these strange and dangerous "jumping fish" make it to Lake Erie? If they do, and these strategies don’t work, what’s next? Even though each expert interviewed had his or her own theory, in the end, they all agreed that it is not a scenario that they’d want to see play out.

Before Attack of the Alien Invaders was broadcasted to a general audience in January of 2011, WVIZ Education produced “LSI: Life Science Investigation,” a multi-media resource created for the classroom. Scott Barber, a teacher in Berea, Ohio, explained how this “fish story,” presented as an interactive mystery, and accompanying classroom resources on the web, has helped his students learn core life science concepts.

The threat to life and limb comes from the carp leaping out of the water when startled by loud noise, like the roar of an engine.  It’s changed life and culture in communities along the Illinois River south of Peoria.  Bath, Illinois, hosts an annual Redneck Fishing Tournament where fisherman compete for the largest haul of Silver Carp either by catching them mid-air with a net or just letting them flop into the boat.  The most recent competition netted nearly nine thousand of the invasive fish.

The changes in the river have been much more dramatic, and destructive, for native species.  The Silver carp and the related Bighead carp are crowding out more desirable fish.  “They are quite prolific and they can compete directly with other fish that eat the plant plankton or animal plankton.  And animal plankton forms the first food for essentially every sport fish species,” says Moy.

That voracious appetite for plankton is the reason Asian carp were first imported to the United States.  Commercial catfish farmers in the South employed them to keep their ponds clean and clear.  But flooding allowed the fish entry into the Mississippi ecosystem.

As carp populations have expanded northward, the fish have gotten closer and closer to Lake Michigan.  If they become established in the Great Lakes, they have the potential to wipe out a seven billion dollar fishery.  “The commercial fishery regularly refers to itself as the largest fresh water fishery in the world” says Peter Annin, author of The Great Lakes Water Wars.

“Once the toothpaste is outside the tube, it's really hard to put it back in.  And so, there's a lot of effort, energy going into preventing these Asian carp from ever entering the Great Lakes,” says Annin.

The most direct route for the carp to reach Lake Michigan is through the Chicago Sanitary and Shipping Canal which connects to the Des Plaines River which flows into the Illinois.  The canal is a man-made link between the Mississippi and Great Lakes water systems constructed over one hundred years ago.  It was a way for Chicago to flush its sewage away from Lake Michigan, the source of its drinking water.

To create a chokepoint to prevent the fish from getting any closer, the US Army Corps of Engineers has maintained an electric barrier on the canal.  “Like a cattle fence that keeps those fish from moving to the next basin,” says Kevin Irons of the Illinois Department of Natural Resources.

The barrier works by sending electrical waves into the water that repel fish.  While it has been proven effective on test fish with transmitters, evidence of Asian carp upstream of the barrier has raised questions and a call to close the canal.

“For years, environmentalists have called for the closure of the Chicago artificial connection,” says Annin.  “They were kind of laughed away.  The laughter has subsided somewhat in recent years because of the threat of the Asian carp knocking on the door of the Great Lakes.”

 Cool Critters Lake Erie Water Snake Educator Guide

Within and along the waters of Lake Erie (one of the five Great Lakes), there is a daily struggle for survival between natives and unwelcome invasive species.  Most times, these unwanted invaders have negative consequences for the lake’s long-standing residents.  However, there are rare occasions when the native actually benefits.

Kristin Stanford, herpetologist, researcher, and snake lover from Northern Illinois University, has been observing this struggle for over ten years as the Recovery Plan Coordinator for the Lake Erie water snake. She works out of Ohio State University’s Stone Laboratory on South Bass Island in western Lake Erie. An expert on these snakes, Kristin, aka “The Island Snake Lady,” works hard to educate students and the public about them, and encourages the islanders to co-exist peacefully with their slithery neighbors.

Lake Erie Water Snake (LEWS)

One of six species of snake found on South Bass Island, Lake Erie water snakes (or LEWS for short) are a species found only in the western basin of Lake Erie, in Ohio and southern Ontario, Canada. The reason the water snakes were listed as a state endangered, federally threatened species in 1999 was due to three primary threats to their population – low population size, habitat destruction, and human persecution.

South Bass Island is a very popular spot for vacationers, with homes built along the shore, boats in the harbor, and hundreds of visitors rattling around the island on golf carts every day. It’s not too far across the water from nearby Cedar Point Amusement Park. Kristin invited us out to the island, one of a series of three small islands – South, Middle and North Bass Islands – to search for snakes.

So, how does one count snakes? Kristin takes a group of five to ten hardy volunteers to fourteen different study sites on the island, to – as she says – “scour the shore line” for all of the adult snakes that they are able to catch.

Kristin’s prime hunting ground is the Scheeff East Point Nature Preserve on the northern point of the island. Our production crew arrived on a hot and humid June morning to find that mayflies had invaded the island, adding to the gross factor of our visit. These insects flew up out of the grass and covered our heads, clothes, and equipment. Luckily, they don’t bite as they don’t even have mouths! Their only career goal is to mate, lay eggs in the lake and die within three days. Once we got used to the mayflies, we turned our attention to snakes.

Hunting for LEWS

At some of their study sites, the researchers place heavy black mats on the ground. The snakes love to snuggle under the mats to keep warm. Kristin warned us that one mat in particular has been doing really well. “When I lift it up, there’s probably going to be about forty snakes underneath.”

YIKES! She wasn’t kidding. There were a bunch, and she gamely grabbed two handfuls of the writhing reptiles. Normally she has several people to help her. Today, she struggled by herself, and managed to get a few into a pillowcase she had brought along as a snake catching bag. And yes, they bite, but they’re not poisonous. She does get bitten in the course of gathering snakes, but they’re usually gone by the next day.

Kristin and her colleagues estimate the number of water snakes by utilizing “mark and recapture techniques.” They insert a small microchip called a pit tag under the skin of the adult snakes they capture, and use the ratio of marked animals to unmarked animals to generate population and density estimates for the Lake Erie water snake.

Kristin plucks a snake out of the grass near the lake shore, and points out the green mark on its back that means it’s been captured and given a pit tag recently. “So what we can do then is scan it and get the pit tag number and re-release it relatively quickly.”

“After we catch the animals, we take some appropriate and annual regular data on them including snout to vent length, mass, we score them for sex and color pattern, and then we also look for the presence of recently consumed prey items. And all that involves is looking for a little bulge inside the snake’s belly. When we see that, we slowly and gently regurgitate that and then we will bring those samples back to the laboratory for further analysis and we identify them to species and that’s how we’re able to determine that the water snakes are eating about 90% round gobies now.”

What are round gobies? No, they’re not fancy marbles. They are a small invasive fish species to Lake Erie, from the Black and Caspian Seas, arriving in the ballast of cargo ships about the mid-1990s. They are considered a very harmful species because they are voracious nest predators for many of Lake Erie’s bottom-dwelling fish and game fish. They gobble up all of the eggs and fry in a very short period of time. And there are BILLIONS of them in Lake Erie now.

So, normally there is not much good to say about an invasive species. But Kristin explained, “It was about the mid to late 1990s when we started seeing gobies pop up in Lake Erie water snake diet samples.”  As they continued to study the snakes, they started seeing more and more gobies popping up in their diet samples, and now, Kristin tells us, round gobies are about 90% of the water snake’s diet.

And what effect is this new menu item having on the Lake Erie water snake? Kristin and her colleagues have been able to show that, since the water snakes have been eating round gobies, “they have increased their growth rate, they’ve increased their maximum body size, so they can grow bigger than they ever could before, they’ve increased their reproductive rate, as well as their survival rate, and population growth rate.” The result – a population explosion of water snakes on the Lake Erie Islands, and also the nearby mainland.

Due in part to the impact of the round gobies, the U.S. Fish & Wildlife Service announced on August 15 that the Lake Erie water snake has been removed from the federal list of threatened and endangered wildlife. And that is – at least from the point of view of the snakes AND the Island Snake Lady – “a really great ending to our story.”

Climate change and invasive species threaten Lake Tahoe just as restoration funding dwindles. (Photo: Lauren Sommer)

Over the last 15 years, more than a billion dollars has been spent to protect Lake Tahoe's clear waters from runoff and erosion. Now, new threats to lake's clarity are emerging, just as restoration funding is drying up.

Researchers from UC Davis are hot on the trail of one of those threats. On a recent late summer morning, Katie Webb and a team from UC Davis's Tahoe Environmental Research Center went looking for it on a boat near South Lake Tahoe.

"So what we're looking for is a metal clam corral," Webb says, pulling on her scuba gear. The "clam corral" is a wire basket that holds clams living on the lake bottom. Webb swims down to it and attaches a rope, so the team can pull it on board.

The clams inside are Asian clams, an invasive species. They were not a welcome visitor when they were discovered in Lake Tahoe in 2002. Webb and her team are monitoring these corralled clams to see how fast the population is growing.

"So you can see this individual is number 11," she says, pointing to a tiny number super-glued on its shell. They use the numbers to track individuals over time. "We can see how much they've grown since we checked them in February and it should be a lot. They grow a lot in the summertime," Webb says.

"What they do is somewhat disturbing," says Geoff Schladow, director of the Tahoe Environmental Research Center. Asian clams filter massive amounts of lake water and that's where the problem starts.

"Of everything they filter, they consume about 10 percent of it and 90 percent they excrete. So their excretions are like these huge nutrient bombs," Schladow says.

UC Davis researcher Katie Webb holds an Asian clam from their population study. (Photo: Lauren Sommer)

With thousands of clams per square meter in some parts of the lake, their "nutrient bombs" help create algae blooms.

"So you have this bright green, stringy algae, sort of clinging to the bottom, a few tens of yards from the beach. People would be astounded to see this cause it looks like any place but Tahoe," he says.

In the face of this invasion, a team from UC Davis has been experimenting with rubber mats that suffocate Asian clams on the lake bottom. So far, the treatment looks promising.

Tahoe Basin Building Boom

Keeping the lake blue – and not green – has been a rallying cry for both environmental groups and Tahoe's tourism industry. Forty years ago, scientists could see 100 feet into the lake. Today, the clarity has decreased significantly to 64 feet.

"We're essentially like a bowl and what happens on the land affects the water," says Julie Regan of the Tahoe Regional Planning Agency. The agency oversees development on both the California and Nevada sides.

"What happened on the land in the 50s, 60s and 70s is that we had a lot of development – rampant overdevelopment," she says. Tahoe hosted 1960 Winter Olympics at Squaw Valley. Casinos went up. Building was booming. And soon, the region had a runoff problem.

"It's driveways. It's houses. What you cover on the land then interferes with the soils ability to filter runoff. That's what's causing clarity loss," says Regan.

Over the past 15 years, local agencies have tried to stop this decline with $1.5 billion of federal, state and local money. They've preserved open space and built projects to control erosion and filter runoff.

"In 2008 we got the news from the scientific community that we had stopped the slide and decline of lake clarity. That was great news," says Regan.

Scientists See Climate Change Impacts

In 2010, however, researchers at UC Davis found the second worst clarity level ever recorded. Geoff Schladow says runoff isn't the only culprit.

"What we've had just in the last few years is this explosion, this large increase in algae and they seem to be concentrated right near the surface," says Schladow.

These algae are invisible to the eye, but they're the right size to make the water look cloudier. Normally, they're competing with large algae near the surface. But Schladow says that's changing. Algae are heavier than water, so they gradually sink.

"The algae in the past tended to be mixed by the wind every few days. So if you're a large algae and you sank down 50 or 100 feet, you could be brought up again into the light by mixing."

Recently, the lake hasn't been mixing as much. The reason, Schladow thinks, is that the surface waters of the lake have gotten warmer with climate change. Warmer water is lighter than the cold, dense water at the bottom of the lake. So it's little bit like oil and water. The layers of the lake are more resistant to mixing.

"Now when we have less mixing, the large algae sink out. All we're left with are the small ones. And so their numbers are going up," says Schladow.

After decades of conservation work to reduce runoff, a lot of people are disappointed to see climate change posing a new threat to Lake Tahoe's clarity.

Schladow thinks it's not hopeless. "It's a call to redouble what we're doing, not to give up and walk away. It's now needed not just to restore clarity but to ward off what may be some pretty uncomfortable and disturbing features of climate change."

Restoration Funds Running Out

After an unprecedented influx of restoration funding, resources are now running low. Senator Dianne Feinstein introduced the Lake Tahoe Restoration Act of 2011 in Congress to authorize more, but has said she's not optimistic about getting it passed.

"We know the funding picture could potentially be bleak, so we're looking to any strategy that we can to keep this momentum going in terms of restoration," says Julie Regan of TRPA.

On top of that, Nevada is threatening to end its forty-year partnership with California by pulling out of the Tahoe Regional Planning Agency, unless concessions are made about its voting power on new development. Regan says it's just one more challenge that will make the next few years a critical time for Lake Tahoe's future.

Lake Tahoe may hold mysteries. Photo: Santappa.

A few weeks ago, scuba divers in Lake Tahoe found the body of a man who had drowned in the lake 17 years ago. Still in its wetsuit, the body was very well preserved. Because the water in this high alpine lake is so cold, decomposition is very slow. This fact has spawned rumors, the most famous of which involves Jacques Cousteau and still makes me shudder, years after I first heard it. Apparently, years ago, Cousteau went scuba diving in Lake Tahoe. He emerged from the water shaken, but not with cold. He said, “The world is not ready for what I have seen.”

What did Cousteau see? Maybe the bodies of unlucky gamblers who crossed the Mafia in 1950s Reno. Or maybe it was Tahoe Tessie, the Loch Ness likeness of the lake. But, in its coverage of the recent discovery, the LA Times said that Cousteau never actually visited Lake Tahoe. The Cousteau story may be a myth, but it is no less chilling, because the physical conditions of the lake are such that bodies could still be drifting beneath the surface.

At 1645 feet (depending on the level of water in the basin), Lake Tahoe is the second deepest lake in the US. (Crater Lake in Oregon is the deepest in the country. The world record goes to Russia’s Lake Baikal, which is some 5,369 feet deep.) Lake Tahoe is located between two fault zones, and it formed through a tectonic combo of uplift and subsidence. The Sierra Nevada mountains rose up on the west and the Carson Range rose up on the east. The rock underneath the lake sank down to form a flat-bottomed basin called a graben. The word is German for “grave” and refers to the lake’s low-lying nature—and perhaps also to whatever Cousteau purportedly saw underwater.

Lake Tahoe is cold. The temperature at the surface of the lake varies, from a low of about 40 degrees in February or March to a high of about 75 degrees towards the end of the summer. Below the surface, the temperature is a chilly 39 degrees. In the winter, when the surface and the deep waters are relatively close in temperature, the wind blowing across the surface of the lake mixes the water. This brings oxygen from the surface layer down to the depths, and nutrients from the depths up to the surface.

In 2010, the mixing occurred from the surface down to about 550 feet, because the surface of the lake remained relatively warm throughout the winter. In previous years, mixing has occurred down to about 1500 feet. Since the 1970s, the surface layer of the lake has gotten warmer in the summer, and it retains that heat throughout the winter. Just like in the ocean, stratification—a warm surface layer that is distinct from the cold bottom layer—means it is hard to get the surface and deep waters to mix.

Lake Tahoe is famous for its clear waters. But, as UC Davis’s recently released Tahoe: State of the Lake Report explains, the lake is not as clear as it used to be. In the 1960s, you could see down to a depth of about 100 feet, but now you can see down to only about 70 feet. The lake has become cloudier because nutrients enter the lake via 63 rivers and streams, and those nutrients fuel the growth of algae. And, global warming plays a role: the warm surface of the lake gives a particular species of microalgae a competitive advantage, and the tiny bodies of the microalgae cloud the water.

The clarity of the lake, and its invasive species, will be on the agenda today at the Lake Tahoe Environmental Summit. Nevada Senator Harry Reid and California Senator Dianne Feinstein will both be at the Homewood Resort, discussing Lake Tahoe’s economic and ecological challenges.

Grasses blow in the wind near Toms Point in Marin County, on the east side of Tomales Bay. Most of the grasses in the photo are exotic. Photo: Brody Sandel.

Full disclosure here: Brody, Emily and I were all grad students together in the same lab at UC Berkeley. So when Emily told me she had a new paper, I was curious to see what it was all about. It turns out their study is really cool. It looks at the interaction of two major world-changers: invasive species and climate change. Their paper talks about exotic species—species that are not native to a particular habitat but are not necessarily detrimental, and noxious weeds—species that are somehow disruptive, because they outcompete native species or alter the habitat. Noxious weeds are what we would also call invasive plants.

Brody and Emily’s study draws on existing datasets on current plant distribution across the state, plant traits, and current and future climate. They mapped the distribution of all the different species in California grasslands, using data from the Jepson Manual (the bible of California plant life), and a few other sources, to fill out an 800-cell grid of the state. They looked at the traits of the species—including how tall the plants are, whether they are annual or perennial, how much of their leaf mass comes from nitrogen, and the size of their seeds—and examined how the traits relate to the climate where the plants live today. Especially important was the proportion of exotic species in each of the grid cells. Then they turned up the temperature. They predicted the proportion of exotic species in each grid under climate change scenarios: higher average temperatures and less available water.

They found that as the temperature increases and water availability decreases, the proportion of exotic species increases. And, the proportion of noxious weeds increases. Higher temperatures favor traits that tend to be possessed by exotic species, such as tall plants with big leaves and annual lifestyles. These are the same traits that made the plants successful invaders in the first place. For example, a tall plant extends above a short plant, stealing its light. But burly exotic plants like Holcus lanatus outcompete native species for light. And generally, plants with big seeds grow to be hearty seedlings, which are better competitors than scrappy little seedlings grown from modest sized seeds. This study predicts that noxious weeds will become even more prevalent, because they have traits that will serve them well under the conditions of climate change. The changing climate acts as a filter, straining out the native species.

The noxious weed Holcus lanatus, a.k.a. “The Hulk,” so named because it towers above native grasses and outcompetes them for light. Photo courtesy of Brody Sandel.

Years ago, I asked a grad student friend why she studied grasslands. I just couldn’t understand the appeal of a field of grass—it seemed boring. My friend Tasha explained that she just loved the way grasses look when they blow in the wind. A few weeks later, I went with her to her field site near Point Reyes, and I immediately understood the aesthetic appeal of grasslands. If you’re picturing a green manicured lawn with short little blades of grass, toss that idea right now. Instead, think of taller grasses, shin height or higher, in all shades of green, brown, gold and even purple. Think of the colors shifting as the wind blows. It is really a beautiful sight. California’s grasslands are expected to expand as the climate changes. But the inhabitants of these grasslands won’t be the grasses that were there 100 or 200 years ago. Instead, there will be a bunch of weeds blowing in the wind.

To learn more about the interplay between California’s native plants and exotic species, check out the California Native Plant Society, the California Invasive Plant Council, or take a workshop with the Jepson Herbarium at UC Berkeley.

San Francisco Bay is home to hundreds of invasive species. Many arrived in the ballast water of large ships.

Hundreds of invasive species have been found in San Francisco Bay, according to biologists. That makes the bay one of the most invaded estuaries in the world.

Hoping to restore native fish and wildlife, California has passed the strictest rules in the country to prevent ocean freighters from introducing more foreign species to the bay. But the standards are so tough, officials may not be able to enforce them.

"Let's see we've got one, two, three exotic organisms, four exotic organisms…"

On a muddy beach in Alameda, Biologist Andrew Cohen of the Center for Research on Aquatic Bioinvasions scoops up a clump of seaweed that’s home to clams, snails, and strange globs.

"Those yellow dots are the eggs, the egg mass of a Japanese sea slug which show up here a few years ago." Almost all of the animals in Cohen's hands are invasive species – originally from places like China, Australia, and the Atlantic.

Listen to the QUEST radio story Combating Bay Invaders

"Anytime I go out in the bay, there's a reasonable chance I'm gonna find something I've never seen in the bay before – something no one has seen on the Pacific coast before. That's just astonishing," says Cohen.

Most of these marine invaders arrived as international hitchhikers. Ships that carry cargo on the open ocean have to be balanced, so they don't tip over. To do that, they fill massive onboard ballast tanks by pumping water in at one port and pumping it out at the next.

"For a long time, people didn't think too much about this, cause it was just water. But eventually, we found that we were moving virtually everything that lived in the sea," Cohen says.

Marine organisms like crabs and snails have tiny free-floating larvae. So, a tank full of ballast water is like a soup of marine life. "They're so effective at dispersing because a single individual might produce a million young."

Some invaders have brought parasites that cause swimmer's itch at local beaches. Other foreign species, like the Asian clam, have altered the entire food web in San Francisco Bay. Millions of dollars have been spent trying to eradicate the worst invasive species. But Cohen says those efforts rarely work. So, the strategy has turned to prevention.

Testing New Treatment Technology

Inside the Golden Bear, a 500-foot ship at the California Maritime Academy in Vallejo, Engineer Bill Davidson switches on the ballast pumps. "The ballast tanks we use are right above us, which are our treatment and control tanks," says Davidson.

Davidson is testing new ballast water treatment technology. The idea is pretty simple – kill the organisms in the water, so they don't spread when the ballast is released. The system has two steps. First the ballast water is filtered. Then, chlorine is added. "And you take this chlorine and you feed it back into the ballast stream and so that will ideally oxidize or kill any live organisms," says Davidson.

The chlorine is neutralized before it’s released by the ship. But getting this system to work is trickier than it seems, because the organisms are very, very small.

In a lab on the ship, Julie Kuo of Moss Landing Marine Labs looks through a microscope at a tiny, cone-shaped plankton. "So right in your center field of view… That's a tintinnid and those guys pretty much get to as large as that."

"As large as that" is about half the width of a human hair. As part of the tests, Kuo counts the organisms in water samples from the treatment process – and, most importantly, sees if they're dead. "If they’re kind of sitting there and you don’t know if they’re alive or dead, you poke them with a probe," says Kuo.

The Frontlines of Regulation

This treatment system is designed to meet international standards that limit the number of living organisms in ballast water. Right now those standards are voluntary.

But California has adopted a goal that’s a thousand times tougher. It applies to all newly-constructed ships starting next January. The only problem is – the technology to meet California’s higher standard isn’t quite ready for prime time.

"We aren’t going to be able to go out there right now and say well, 100% you met the standard no matter what," says Nicole Dobroski with the California State Lands Commission, the agency overseeing the regulation.

She says none of the treatment systems being developed consistently meet California’s standards yet. Still, the state is moving ahead with the regulation.

"We recognize that that’s a challenge, but there's a good reason we wanted it to be a challenge. We wanted them to be innovative. We wanted them to think out of the box."

But ship operators may not have much to worry about if past enforcement policies are any indication. Ships are currently required to exchange their ballast water at least 230 miles from shore if they plan on discharging it in port. But even though hundreds of ships a year are not complying with these requirements, the State Lands Commission has only fined two ships in the past ten years.

"Our goal isn't just to come in and slap a fine on these vessels because we find that isn't necessarily the best approach. We try to work with them as much as possible, make sure they’re educated about all the necessary regulations," says Dobroski.

California's progress is likely to have a big impact on federal efforts as both the US Coast Guard and the EPA develop new national ballast water standards.

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Wildfire ripped through this area of forest, which was infested with Sudden Oak Death. Does infestation with SOD make wildfires burn with more intensity? Photo: Kerri Frangioso.

From Oregon to Big Sur, potentially millions of trees have been killed by Sudden Oak Death, or SOD. In 2006 and 2007, researchers from UC Davis set up a large-scale study in the coastal forests near Big Sur to examine the spread of the disease and its impact on forest dynamics. The area was one of the first to be affected by SOD. Members of the Rizzo Lab at UC Davis had established 280 plots across the region, carefully counting and measuring each tree and checking for SOD infection. Then, in June 2008, the Basin Complex Fire ripped through Big Sur, burning over 95,000 hectares of forest. By the time the fire was contained, over a month after it began, one third of the team’s plots were crisp and blackened.

While the fire burned, news media and firefighters assumed that areas of the forest infested with SOD would burn more intensely—all the dead oak trees would fuel the fire. But the natural experiment created by the overlap of the Basin Complex Fire and the UC Davis study allowed researchers to test whether SOD did in fact make wildfire worse. Their study will soon be published in the journal Ecological Applications; a preprint of their paper is available here. What they found was not what the news media or the firefighters predicted.

Andrew Molera State Park, the same plot as the top photo, before the Basin Complex Fire. Photo: Kerri Frangioso.

Invasion of the water molds
Sudden Oak Death came to California in the 1990s, probably on the leaves of a rhododendron shipped in for the nursery industry. The disease is caused by a water mold, called Phytophthora ramorum. It can spread short distances in splashes of water, and can potentially travel longer distances when water is blown about in storms.

Not all trees that are infected with the pathogen will die. Some species, like California Bay Laurel, do just fine. But California Bay is like Typhoid Mary—it serves as a host to the pathogen and allows it to spread to other, more susceptible species. The pathogen is fatal to tanoak and several species of oak trees. These species develop cankers on their trunks, which bleed out a thick, red liquid. Slowly, the bark around the entire circumference of the tree is affected; all tissue above this girdle dies, leading to the death of the tree.

A natural experiment
In 2008, Margaret Metz had just begun a new post-doc in Dave Rizzo’s lab. She was to work on the Big Sur project and analyze the data from the 280 plots to understand SOD impacts in the region. Her colleagues had spent months setting up the plots for their SOD study. They knew the size and location of every tree, whether it was standing upright and healthy (or newly infested with SOD), or whether it was dead and decomposing on the ground. When Metz found out her study site was burning, she was devastated. All that hard work—and all those trees—was going up in flames.

However, the dismay was short-lived. The team had a perfect pre-fire dataset. They just needed to census the plots after the fire, to get a rare comparison of the severity of fire in areas with and without SOD. This was an experiment they didn’t intend on doing—but drought and a dry lightning strike had made it possible. Dave Rizzo was able to quickly procure funding for the researchers to re-census the plots. “You could never do a controlled burn on that scale,” says Metz.

Where there’s SOD, there’s more intense fire?
News articles about the Basin Complex fire linked SOD to fire intensity, and firefighters reported that fires were burning more fiercely in areas with evidence of SOD. So when Metz and her colleagues analyzed their data, they thought they’d see that fires were more severe in plots infested with SOD. But that is not what they found. Their data showed that plots with and without SOD showed no difference in fire severity. They quantified fire severity using something called the Composite Burn Index. It takes into account the effects of fire on the ground, as well as in the shrubs and trees. Composite Burn Index did not differ between plots infested with SOD and plots without SOD. The popular assumption, that SOD makes wildfires burn more intensely, was wrong.

Dead tanoak along the Big Sur Highway. Photo: Karl Buermeyer, COMTF.

However, Metz and the team could dig deeper into their data. From their pre-fire data, they knew whether SOD had infested the plots recently, or whether SOD had been there for some time. It can take several years for a tree to die from SOD. When trees are first infected with SOD and die, their leaves turn dry and brown, and they remain on the tree for a year or more. Later, the branches fall to the ground, and eventually the whole trunk falls over. The fuel created by newly infected trees and trees that have been infected for several years is quite different. Metz and her colleagues found that in plots that were newly infested, plots with more dead biomass (or fuel) burned more intensely. In plots that were infested some time ago, the amount of biomass was not related to the intensity of the fire. They suspect that crisp brown leaves on newly infected trees allow the fire to burn high in the canopy. In plots infested long ago, the dead trees are on the ground; in this case, the fire damages the soil and the tree roots, which makes slopes vulnerable to erosion from mudslides. The conventional wisdom about SOD and fire was not quite right, but there was some truth to it—it just depends on when the forest was infested with SOD. Newly infested forests burn with more intensity than un-infested forests or forests that were infested some time ago.

Future forests
It has been almost three years since the Basin Complex Fire burned up Metz’s plots. Now, she and her colleagues are looking to see how the forest recovers—from the fire, and from SOD. Maia Beh, a grad student in the Rizzo Lab, found that of the plots that had SOD in the pre-fire surveys, only 20% still have it today. They’re not sure whether it’s because of the fire, or because there have been two years of drought. The pathogen, P. ramorum, is dependent on water, and doesn’t do well in drought conditions. They’re looking at plots that did not burn up in the fire to see whether the decline in the pathogen is due to drought, fire, or some combination of the two.

Though the incidence of the pathogen has declined on land, it is still present in almost all the watersheds in the area. And, last year we had late rains, extending through spring into the early summer. Late rains with warm temperatures create conditions that are ideal for the pathogen, says Metz.

With continued careful sampling of those 280 plots—and maybe a few more unintended natural experiments—Metz and her colleagues will learn how forests recover from both fire and SOD.

Learn more about SOD
To prevent the spread of the pathogen P. ramorum, take steps make sure it isn’t hitchhiking on your boots. Clean your boots into the buckets of diluted bleach that you might find at trailheads, or spray your boots down with Lysol.

Take part in a SOD-blitz, a citizen science project. Learn more about SOD and help figure out where the pathogen has spread, with UC Berkeley plant pathologist Matteo Garbolotto. You can see Garbolotto on the QUEST video Plant Plague: Sudden Oak Death.

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