June 11, 2013
Pennsylvania is mussels-rich--there are about 168 species of the freshwater variety in the state’s rivers and ponds. But that wealth has been threatened over the past few decades by pollution and industry which encroach on the mussels’ habitat.
Tim Pearce is in charge of cabinet after floor-to-ceiling gray metal cabinet of mollusks at the Carnegie Museum of Natural History in Pittsburgh. Some contain bivalves, or--marine animals with a hinged shells. Within this category are freshwater mussels, including one of Pennsylvania's most endangered species, the Eastern pearlshell mussel.
Pearce says there are only about two populations left in Pennsylvania. They’re mud brown on one side, but pearly, pink and purple hued on the other, like the color of the sun setting through clouds.
"They’re really having a hard time here, and we’re not quite sure why these are having a much harder time than the other ones," says Pearce.
The shells in the collection are just the remnants of animals collected over the last 100 years or so. Many were added to the collection when freshwater mussels were more abundant in the region. Some are now extinct. Freshwater mussels wedge themselves into the bottoms of rivers and streams, and some ponds. Their outside shells camouflage them--making them seem like rocks in the riverbed. As they suck in water, searching for food, they expel that water, cleaning it as they go. All that hoovering is great for rivers, but pollution and industry, like mining and gravel dredging, can add more impurities to the water than the mussels can handle.
Pearce says the almost peculiar life cycle of the mussels has a lot to do with their decline, too. For example, Yellow lampmussels are famous for having a lure which looks like a little minnow, complete with an eye spot. Like all freshwater mussels, this species reproduces by tricking a host fish into carrying its fertilized eggs for the remainder of their growing up period, like fish daycare. The lure is the trick. The fish thinks it’s getting a tasty minnow snack, but instead gets a face full of baby mussels. What sounds like a slapstick routine is a crucial process. It’s how mussel populations get from one part of a river or stream to another.
"A lot can only do this metamorphosis on a particular species of fish, so if the fish is no longer living in this water body, the adults can still continue to live, but they can’t reproduce," Pearce says.
In some cases scientists still don’t know exactly which fish match up with certain mussels species. And a new study shows fish populations are reduced by the same gravel dredging which impacts mussels. Climate change is also a risk. Both Yellow lampmussels and Eastern pearlshell mussels are listed as vulnerable to climate change on a statewide index. Increased rainfall in the state could cause flooding--sending more debris into rivers and streams. And then there’s the increase in temperature. Pearce says if the temperature rises and mussels are at southern edge of a range, where the climate is the warmest they can tolerate, they may not be able to tolerate an increased rise in temperature.
How freshwater mussels will tolerate Utica shale drilling is also a question. Drilling operations have recently begun near French Creek, where freshwater mussels have made a comeback, and are thriving.
Groups like the Western Pennsylvania Conservancy are working to ensure that continues. They’re monitoring water flow in the area which includes French Creek, and their findings could inform water management practices that help protect the habitats of mussels and fish.
Pearce takes the long view. He’s scientist in a museum, surrounded by years of meticulous research and proof that these mussels have been successful in the region. And he says more is known about mollusks everyday. But he’s also cautious.
"We’ve always had things going extinct. It’s just that nowadays, things are going extinct much more rapidly. And it’s so easy to show that we humans are a major cause of that," he says.