Target life cycle stage: Settled juveniles and adults.
As mentioned in the Impacts section and the Life History and Biology section<, there are numerous naturally occurring substrates on which zebra mussels will settle. A successful monitoring strategy using natural substrates will depend on the types of natural substrates that are available in the habitat. Either qualitative or quantitative data may be obtained, depending upon the substrates chosen. In habitats with substrates composed of sand and silt, little woody debris, and many macrophytes, artificial substrates might be more practical samplers than naturally occurring ones. Avoid utilizing macrophytes as a substrate for quantitative sampling since it may be difficult to quantify the surface area involved. However, aquatic plants are an excellent substrate for providing data on mussel presence or absence.
Prior to analyzing zebra mussel samples, ensure that proper containment protocols are observed (see Protocol for Responsible Monitoring Procedures section for further details).
Qualitative analysis:
Simply remove the natural substrate, record the presence or absence of adult mussels, and replace the substrate. Areas with higher zebra mussel densities may lend themselves to the use of either a Ponar grab or a coring device. Be sure to obtain an appropriate number of replicates.
Advantages: Relatively rapid, no elaborate deployment tactics needed, little worry of vandalism, and field analysis possible.
Disadvantages: Provides no measure of mussel abundance in a habitat.
Quantitative analysis:
This sampling approach involves the enumeration of mussel density. At the time of substrate collection for quantitative data in areas with low densities, survey the habitat for the availability of the substrate collected using a 1-mē quadrant. If unionids are used, record the average number of unionids/mē. If substrates such as boulder, cobble, or large woody debris are used, record the percentage of available substrate contributed by the particular substrate used. The substrate must have a surface area that is readily quantifiable. Surface area of boulders, cobbles, and unionids may be quantified by approximate geometric formulas or digitizing (if the shapes lend themselves to this) or by the foil method. To obtain surface area using the foil method, clean the zebra mussels from the substrate. Completely cover the portions of the substrate exposed to the water column as accurately as possible with a single layer of aluminum foil. Gently remove the foil wrapping from the substrate and weigh it on a balance. Use the weight of a 1-cm square piece of foil to calculate the area of the foil used to wrap the substrate in question. After counting all of the mussels found on the substrate, use this area to report the observed mussel density. To calculate large woody debris surface area, its usually best to subdivide the piece into appropriate geometric units whose dimensions can easily be measured. For instance, if the debris is a wooden branch with a radius of 4 cm and a length of 109 cm, its surface area can be calculated easily using the formula for the surface area of a cylinder (2 r [r+1]).
Advantages: Provides a measure of abundance in a habitat.
Disadvantages: A more complex approach to sampling, requiring greater effort.