Voracious invasive quagga mussels gobbling Great Lakes' food chain
Oct 02, 2011 (Menafn - Detroit Free Press - McClatchy-Tribune Information Services via COMTEX) --They eat as much as 98% of their weight each day, multiply rapidly and could alter the Great Lakes forever.
No, they aren't Asian carp. They are the true scourge of the lakes: quagga mussels. Their exploding numbers and rapid spread are leading scientists to use words like "startling," "dramatic" and "unprecedented."
"Quaggas are causing the biggest changes we've ever seen in Lake Michigan," said Tom Nalepa, a research scientist at the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory who has studied the lake for more than 30 years. "The numbers are still going up. We are going to see more severe impacts."
Quaggas are in four of the five Great Lakes. The havoc they have created includes an increase in toxic algae, a loss of tiny plants and animals that fish feed on, a decline in prey fish, and skinnier game and commercial fish.
Quagga numbers are staggering. Nalepa estimates that there are 437 trillion quaggas in Lake Michigan alone, based on 2010 surveys. "I had to double-check my zeros," he said.
That's about 45 million quaggas for every person in Michigan.
MUSKEGON -- The Jensen and Petersen families have been commercial fishermen in Lake Michigan for almost the past century.
These days, they're having to go farther and deeper than ever to find enough whitefish to fill their annual combined state quota of half a million pounds.
They used to be able to find fish at 90 feet; now, they've won permission from state fisheries managers to go down 150 feet in search of enough to keep their business going. The whitefish have spread out and moved deeper in search of food.
This year, the two families even tried old fishing grounds an hour and a half south, where they once had success. "The fish were not there," said Paul Jensen, 66, whose younger brother David goes out on the trawlers. "We see the changes. Our fishery is being hugely impacted by invasive species, and the public has no clue."
The main culprits are the quagga mussels that now carpet the bottom of Lake Michigan, filtering out all the food above them. Diporeia, a tiny shrimp that used to be the main source of food for whitefish and many other species, have all but disappeared from the lake, according to scientists. The mussels appear to have sucked up the phytoplankton that once fed the shrimp.
Tom Nalepa, a scientist with the National Oceanic and Atmospheric Administration, has studied the Great Lakes for nearly 40 years. He couldn't believe what he was seeing at first as diporeia, which have been in the lakes since the glaciers receded to form them, began to disappear. "I thought it must be a pollutant," he said. "They went from 10,000 per square meter to zero in six months" at one sampling station in Lake Michigan.
Gary Fahnenstiel, also a scientist with NOAA, calls quaggas the greatest disruption to ever hit the lakes. "Based on their effects, I'd argue quaggas are a greater perturbation than alewives or sea lamprey," two other major invasives, he said.
Quaggas have turned Lakes Michigan and Huron into clear, sparkling lakes that are beautiful to look at and swim in, but the dark side is that the lakes are actually biological wastelands as trillions of mussels have cleared the water of food other creatures need to survive. Quaggas have exploded in the lakes just since about 2003.
"Lake Michigan now looks like Lake Superior and is probably the clearest it's been in 5,000 years," Fahnenstiel said.
Mussels outweigh lake's fish
In Lake Michigan, the most affected, the biomass -- or total weight -- of quagga mussels is now four times the biomass of all the fish, said Nalepa. That's a huge change just since 2005, when fish biomass was more than twice the mass of quaggas, he said.
At the same time, another invasive species called the spiny water flea, about half an inch long with a long, thorny tail, is also colonizing the lakes after arriving in ballast water in 1984. It's tangling fishing lines and eating miniscule animals called zooplankton that provide food for fish.
David Bunnell, a fisheries biologist with the U.S. Geological Survey, pointed to a photo of the results of a 2008 trawl along the bottom of Lake Michigan. The catch was separated into four piles: smelt, round gobies, alewives and quagga mussels, all invasives. "Sometimes, that's all we see," he said.
In September, when Bunnell and colleagues trawled the deep bottom of Lake Michigan during a scientific survey, the nets were so heavy with quaggas, they burst the knots at the bottom of seven nets on seven different trawls. On the eighth try, the crew double-knotted the net and brought up thousands of pounds of virtually nothing but quaggas.
"I've never seen anything like it," Bunnell said. Quaggas plague other lakes, too. In 2007 in central Lake Huron, there were about 25 trillion quaggas, but that number would be far larger now and excludes the lake's large bays, Nalepa said. Lake Ontario is similar, but Superior has too little calcium for them to form shells.
In shallow Lake Erie, the split between mussel populations is about half zebras and half quaggas.
"If you'd told me a decade ago something would replace zebra mussels, I'd have said you were nuts," Fahnenstiel said.
Zebra mussels disappear
Zebra mussels are more famous than the slightly larger quaggas, but most people don't realize zebras have virtually disappeared from Lakes Michigan and Huron.
Zebras arrived first, in 1988, in the ballast water of foreign ships. Quaggas followed in 1989.
Zebras spread rapidly close to shore, clogging water pipes and costing water treatment plants millions of dollars. Quaggas were still under the radar until about 2000, when they began moving into the deep parts of lakes. Quaggas, which can outcompete zebras, then took over.
Zebras are managing to survive in shallow, warm spots such as Saginaw Bay and western Lake Erie, but Lakes Ontario, Michigan and Huron are now 95%-99% quaggas, scientists say.
By providing a new source of food for them, invasive mussels also have helped round gobies to explode in the lakes. Gobies arrived in ballast water about 1990; they now make up 10%-20% of the fish biomass in Lake Michigan.
Spiny water fleas have also exploded recently, especially in Lake Huron.
Zooplankton, once an abundant food source for others in the food chain, are under siege, eaten by the spiny water fleas. In Lake Huron, the water fleas appear to be eating even more plankton than fish, Bunnell said. They also appear to be forcing zooplankton to dive deeper to evade capture. That makes it hard for fish to find them, and at lower, colder depths, the zooplankton are less able to grow.
Some fish, deprived of food such as diporeia, are also eating another native shrimp, the possum shrimp, which used to be abundant.
"This is all happening both from the bottom up and the top down" in the food chain, said Bunnell. "Zooplankton and prey fish are getting squeezed from both directions."
Researchers have also found that an important spring bloom of phytoplankton, tiny single-celled plants and animals that have served as food at the base of the food chain, is disappearing. Mussels are gobbling it up faster than the plankton are produced.
Scientists first documented the bloom in Lake Michigan, shaped like a doughnut, around 1998. The ring has likely been there for thousands of years but was visible only with improved technology and a reduction in ice cover, said Charles Kerfoot, a scientist at Michigan Technological University, who found the ring.
Now, quaggas have filtered out most of the doughnut -- about 70% of the spring bloom is gone.
"First, we discovered it, and now it's vanished," Kerfoot said.
Mussels are also implicated in the growth of toxic algae, which can make people and pets sick. The mussels filter good algae out of the water as food, but spit out toxic blue-green algae. That means the toxic algae has less competition once the good algae is gone, and can grow more abundant. Huge blooms in the past two years on Lake Erie are partly the result of the concentration of zebra and quagga mussels in the lake, as well as levels of phosphorus that keep rising from agricultural runoff into the lake. The blooms in the lake are as bad as they were in the 1960s and 1970s, after several decades without them, said Don Scavia, a University of Michigan professor.
Skinny, unhealthy catch
The complex changes in the food web are hurting not just fish, but the humans who depend on them to make a living.
Although some fish, such as whitefish, are learning to eat quaggas and spiny waterfleas, the new diet items are tougher to digest. That leaves the fish skinnier and less healthy.
"Diporeia was a Snickers diet for whitefish," said Jensen in Muskegon. In the past, the fish would go from egg to mature enough to reproduce in 16 months; now they grow so slowly, it can take five years, he said.
Another species his family and the neighboring Petersens used to haul in were bloaters, also called chubs, to sell smoked. They feed on phytoplankton, and as that diminishes, the chubs are fewer, smaller and harder to find.
"Chubs were 25%-50% of our business," said Eric Petersen, 35, scrubbing out the fish cleaning stations on a warm fall afternoon. "We had some years when we did well, but the catch has slowly dwindled."
Jensen scoffs at the idea that Asian carp could make it in these waters. "That's overblown," he said. "We're missing the bigger issue." There's not enough food left for Asian carp, which feed on plankton, after the huge quagga invasion, he said.
Fortunately for sport fishermen, salmon are still healthy in Lake Michigan, but biologists aren't sure whether that will continue.
Lake Huron has suffered a collapse of salmon, the state's most popular sport fish, partly because of food web changes. But the stock has been healthier in Lake Michigan because of steps taken by state fish managers.
This year, salmon are plentiful, but whether that lasts is impossible to predict, said Dan O'Keefe, a Michigan Sea Grant educator who works with sport fishermen on Lake Michigan. "I don't think this year means we're out of the woods," he said. "People are still concerned."
'Cut off the tap'
Short of a disease or poison that could be targeted at them in the lakes' depths, quaggas are here to stay, Nalepa said.
But they represent a lesson for the future.
Of the 186 invasive species in the Great Lakes, two-thirds came from ships in the St. Lawrence Seaway, which pick up ballast water in foreign ports and discharge it into the Great Lakes. "We need to cut off the tap," said Kerfoot.
The lakes need a rest so that species already here can adapt to the new realities, Fahnenstiel said.
"It's all just happening too fast," he said. "The lakes can't take anymore."
Contact Tina Lam: 313-222-6421 or tlam@freepress.com
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