Ron Klauda studied a row of buoys freshly pulled that morning that had been marking areas of the Sassafras and Elk River, Susquehanna Flats and other parts of the Upper Bay since being placed in the water last spring.
"They're cleaner than I thought they would be," the Maryland Department of Natural Resources biologist remarked.
He had expected them to be covered with mollusks and other fouling organisms, but most looked like they were ready to go into the water, rather than having just been pulled out.
Nonetheless, Klauda set to work examining each buoy, both visually, and by running his hands over them, feeling for tiny mollusks that might be barely larger than grains of sand. To be precise, he was in search of zebra mussels, a notorious invader that showed up off Port Deposit, MD, just a few miles upstream from the mouth of the Susquehanna River, in the summer of 2010.
This summer, another mussel was found by a citizen in the nearby Sassafras River. A follow-up inspection of docks, piers and buoys in the area by DNR biologists found no other zebra mussels. That single individual was a full-grown adult, and Klauda suspects it's unlikely that it's the only one that has escaped the Susquehanna, where the creatures have been working their way downstream for the last decade.
Biologists in the Bay region have long been concerned about the arrival of the species, a native of the Caspian Sea, because of its ability to mushroom into huge populations, crowd out native mussel species and alter ecosystems.
Because they are a freshwater species, Klauda and other biologists think it's unlikely they will thrive in the Bay, but they could easily be transported to other rivers where they could take up residence, especially in lakes and reservoirs.
But he and others are concerned that high river flows this spring and fall, which dramatically reduced salinities in the upper Bay, may have hastened the mussel's spread. Hence his interest in inspecting buoys that DNR crews pull from the water before winter each year.
But those same high flows, particularly those in the wake of Hurricane Irene in late August followed by Tropical Storm Lee in early September, appeared likely to have erased evidence of zebra mussel spread by scouring the buoys as the sediment -laden water charged by. "That's the cleanest we've ever seen them," said Ben Gillis, an engineer on the DNR ship, the A.V. Sandusky, that pulls the buoys each fall.
Otherwise, Klauda's plan was solid. Zebra mussel larvae attach to solid substrates and begin growing, often forming dense colonies. Scientists on the Hudson River tracked their spread in tidal reaches by monitoring their presence on buoys. In the Great Lakes, where zebra mussels arrived in 1988, buoys have reportedly sunk from having so many mussels grow on them.
Named for the striped pattern of their shells, zebra mussels are thought to have arrived in the Great Lakes in 1988 in the ballast water holds of ships from Europe. They have been a major nuisance for industrial and municipal water uses as their dense colonies can block water intake pipes. They can also coat boat bottoms, cables and any other hard surface, and have been blamed for billions of dollars in damages nationwide.
An individual zebra mussel can filter up to a gallon of water per day while feeding on algae. That has had dramatic impacts on water clarity - visibility in parts of Lake Erie increased from 6 feet to 30 feet after the mussels invaded. That doesn't necessarily mean better water quality, though. Zebra mussels arrived in the tidal portion of the Hudson River in 1991. The large mussel population that developed since resulted in reduced dissolved oxygen levels, as the mussel population used up oxygen in the water faster than it could be replaced.
Their filter feeding promotes some algae species and suppresses populations of others. In the Hudson, that has led to an increase in phosphorus exports from the river. Zebra mussel populations in some lakes have been linked to the formation of toxic blue-green algae blooms.
In some places with large populations, zebra mussels have reduced the food supply for fish, causing their populations to fall. Competition with the zebra mussels has nearly wiped out native mussels in areas.
Because their larvae latch onto boats and can be carried on vegetation clinging to boat trailers, they are easily transported from place to place. Since their arrival in the Great Lakes, they have turned up in much of the rest of the country.
The biggest challenge in controlling their spread is maintaining public awareness and vigilance by water users to make sure they are not inadvertently moving the mussels around. "We have to act like it's a big deal all the time," Klauda said.
Zebra mussels showed up in the Susquehanna headwaters in New York in 2000 and quickly began expanding their range. But their status in the rest of the watershed is uncertain. Few mussels have been reported in Pennsylvania except near the New York and Maryland borders.
In part, scientists say that may reflect the fact that zebra mussels fare better in lakes and reservoirs than they do in free-flowing rivers. But it's also likely that they are being overlooked.
"The flaw to the monitoring network is that it is volunteer," said Sarah Whitney, who coordinates the zebra mussel monitoring program for Pennsylvania Sea Grant. "We rely on people who are out doing other water quality sampling to also look for zebra mussels. So it is not a comprehensive survey of whole river systems."
It's likely that lots of zebra mussel larvae, known as veligers, are heading downstream as populations in New York are thriving. Tom Horvath, director of environmental sciences at the State University of New York College at Oneonta, said the population continues to increase in Lake Otsego, the source of the Susquehanna 444 miles upstream from the Bay.
"I have collected hundreds of thousands of adult mussels out of the lake," Horvath said. "They are all over the place. That is a typical invasion scenario there. Everything you pull out of that lake has mussels on it."
Closer to the Bay, that's not the case, at least not so far. Klauda's inspection of buoys didn't reveal a single mussel, and that was fine. "I didn't really want to find anything," he said.
But Klauda expects to be back inspecting buoys next fall.
Help to stem zebra mussel invasion
Boaters, anglers and other recreational water users can help stop the spread of harmful zebra mussels by taking these simple precautions before launching and leaving the water:
- Remove all aquatic plants and mud from boats, motors and trailers, and put the debris in the trash.
- Dispose of unused live bait on shore, far from any water body, or in the trash.
- Drain river water from boat motors, bilges, live wells, bait buckets and coolers before leaving to prevent aquatic hitchhikers from riding along.
- Rinse boats, motors, trailers, live wells, bait buckets, coolers and scuba gear with high-pressure hoses or hot water between trips to different water bodies.
- Dry everything at least two days (preferably five days) between outings.
- Limit boating from place to place, particularly from the Susquehanna and Sassafras rivers to other water bodies where zebra mussels haven't invaded.
Source: Maryland DNR