Quagga mussels (Dreissena bugensis) and zebra mussels (Dreissena polymorpha) are invasive biofouling mollusks capable of causing severe economic and ecological harm to freshwater habitats. Detecting presence of the mussels as soon as possible after their arrival allows managers to implement responses that can reduce further spread, such as restrictions on watercraft movement. Plankton tow samples collected by CDFW scientists, public utilities, water districts, neighboring states, and federal agencies are sent to the Shellfish Health Lab and analyzed for the presence of the mussels’ planktonic larvae, called veligers.
Cross Polarized Light Microscopy (CPLM)
Mussel veligers have shells made of calcium carbonate crystals that have an optical property called birefringence. Consequently, when viewed under polarized light the veligers produce a distinctive light signature. The veligers’ birefringent property allows samples to be quickly screened using a stereomicroscope. In the photo to the right, suspect mussel veligers are seen using CPLM.
Veligers presumptively identified as those of quagga or zebra mussels by CPLM are viewed at higher magnification using a compound microscope for a more detailed examination of morphology. The organism in the photo to the right was confirmed by PCR and DNA sequencing (see below) to be a zebra mussel veliger
Polymerase Chain Reaction (PCR)
Single veligers are analyzed using PCR to verify identification by amplifying DNA unique to either quagga or zebra mussels. The amplified DNA is observed using gel electrophoresis. The gel to the right shows amplified zebra mussel DNA in lanes 1, 2, 3, 5 and 6. The band in lane 5 is very faint. There is no amplified DNA in lane 4, lane 7 is empty, and lane 8 is reference DNA. Individual bands of DNA are removed from the gel and outsourced for DNA sequencing to confirm the PCR identification.
For more information, please visit the CDFW Invasive Species Program, whose website includes a map of mussel-infested waterbodies in California.