Target life cycle stage: Settled juveniles and adults.
Sampling gear: SCUBA divers or underwater cameras.
Recommended habitat(s): Flowing or nonflowing water.
Type of data collected: Usually qualitative, but can be quantitative.
Visual observation of infrastructure by SCUBA diver
Deployment protocol: SCUBA divers can detect settlement of young mussels by feeling the surface of the structure. Young mussels feel rough (like sand grains) and juveniles and adult mussels can easily be seen by the naked eye.
Recently settled juveniles may be attached to any hard substrate, including other zebra mussels. Here they appear as white grains of sand
Quantitative samples can be collected by using a grid of known size or a quadrant frame and scraping all mussels off the structure surface inside the grid or frame (see Kovalak et al. (1993) for details). In areas of low population density a quadrant of 1 m² may be a reasonable size, but may prove to be too large to count mussels at high population densities. In such situations, a quadrant of 10 cm² may be more practical. Underwater cameras may also be used to view and record the degree of colonization by adult mussels, especially in more remote locations.
Advantages: One of the most accurate ways to determine zebra mussel infestation at a site.
Disadvantages: Mussels must be of a certain size before they can be seen and settling juveniles are less than 1 mm in length. Not all areas can be visually examined, as zebra mussels tend to prefer crevices.