Tuesday, November 27, 2012

What Happened to Pearlshell Mussels in the Hanford Reach?

This is the 2nd installment of this story.  To learn more see our post from July 25, 2012: "Mussels in a Desert?!"

By Joe Bartoszek, Ph.D., Resource Contaminant Specialist, Washington Fish and Wildlife Office

The western pearlshell mussel (Margaritifera falcata) may no longer exist in the Hanford Reach of the Columbia River and scientists Dr. Joe Bartoszek of USFWS and with Doctors Chris Ingersoll of USGS and Dr. Chris Barnhart of Missouri State College are working to find out why.  A 2004 survey in the area found only shells from animals that had died in the past 10 years even though there is plenty of suitable habitat and  they were once found in large numbers. One reason could be contaminants originating from the Hanford Nuclear Site.

The Hanford Reach of the Columbia River, Washington State. Once home to the western pearlshell mussel. 
Photo Credit: Department of Energy

USFWS is spearheading studies with the Hanford Natural Resource Trustee Council to understand what happened to mussels in the river by testing potential sensitivity to contaminants from the Hanford Nuclear Site. The first step was to obtain larval western pearlshell, or glochidia, from another site where the species is abundant and grow them to the juvenile stage for testing.  Raising this mussel species from its earliest stages has never been done before and is a crucial step in understanding their life histories and conservation needs. The next step will be exposing the mussels to contaminants and documenting their response.

Pearlshell mussel collected from the Eel River, CA are readied for larval rearing  experiment. 
Photo credit: Dr. Chris Barnhart  
The life history of mussels is a complex story and there are many differences between the species. During the breeding season, the female mussel is fertilized by sperm that  males upstream release into the water. The fertilized eggs transform into a  larval parasitic stage called glochidia. These glochidia must attach to a host fish before they can continue their development. In many species of mussel, glochidia only attach to one or a few types of fish. For the western pearlshell it is thought that salmon and trout are the preferred host fish. The glochidia live on the gills of the host fish for a few weeks, and then drop off as juvenile mussels.

With the help of Dr. Jeanette Howard of The Nature Conservancy, fertilized female western pearlshell mussel were collected from the Eel River in Northern California in late April and early May, 2012.  The mussels were delivered to Dr. Chris Barnhart at Missouri State University for rearing and glochidia (Step 2 in above diagram) were collected and tested for maturity before being placed on rainbow trout and brown trout (Step 3) at MSU and the Neosho National Fish Hatchery.   Several thousand metamorphosed juvenile mussels were recovered from the host fish (Step 4) beginning in early June.  Some of these have already been used for initial toxicology studies at the USGS Columbia Environmental Research Center and others are being cultured at Missouri State. 

As methods for rearing western pearlshell are perfected we will have a new tool to conduct more studies like the one described here and the potential to restablish mussels in this and other locations where they have disappeared.

Stay tuned for the results of this study on Word from the Wild and check out earlier postings about these mussels.  For more pictures of mussel culturing enjoy amazing photos from Dr. Barnhart: http://bit.ly/TaToaR and this exciting video and podcast featuring American Freshwater Mussels published by Science Magazine.

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