Consultant's Report - Minnesota State Legislature

MINNESOTA DEPARTMENT OF NATURAL RESOURCES
Feasibility Study to Limit the Spread ofZebra Mussels from Ossawinnamakee Lake
mg/l Ca 2 +, with dense populations developing in waters with 2: 21 mg/l Ca 2 + (Mellina and
Rasmussen 1994). Calcium concentrations of 15 mg/l or less were found to limit zebra mussel
development (Mellina and Rasmussen 1994). Negative zebra mussel shell growth was reported
at levels less than 8.5 mg/l by (Hincks and Mackie 1997). Ca 2 + at :s 12 mg/liter is required for
successful zebra mussel veligers rearing (Sprung 1987). Generally, zebra mussel populations are
positively correlated with Ca 2 + concentrations and negatively correlated with P04-3 and NO- 3
concentrations (Ramcharan et al. 1992).
The amount of hydrogen ions in the water, i.e., pH, impacts the ability of zebra mussels to
survive and reproduce in a water body. Claudi and Mackie (1993) found that minimum pH
limits are 6.5 for adult zebra mussels, 7.4 for veligers, and> 8.0 for moderate to maximal adult
growth. Sprung (1987) found that a pH of 7.4 - 9.4 is required for successful veliger
development.
Reponses to Starvation
Zebra mussels feed primarily on planktonic algae and zooplankton, with bacteria, detritus, and
organic matter being alternate food sources. The availability of food sources has been shown to
control zebra mussel populations (Sprung and Rose 1988). In high-density populations, adult
zebra mussels have been known to compete with plankton algae for limited food resources, thus
reducing the survival of the planktonic veligers (Strayer et al. 1996). Under laboratory
conditions, Schneider et al. (1998) suggested that food quality may be a better indicator of
environmental conditions suitable for zebra mussel growth than food quantity. These results
suggest that zebra mussels do not thrive in an abundant suspended inorganic sediment
environment, which is indicative oflarge, turbid rivers (McMahon 1996).
Generally, zebra mussels have a high starvation tolerance. For adult zebra mussels, Chase and
McMahon (1994) reported 50 percent mortality (LTso) occurred after 118 days at 25°C and after
352 days at 15°C with no source offood. One hundred percent mortality (SMlOO) occurred at 143
and 545 days at 25°C and 15°C, respectively. In laboratory experiments, Sprung (1989) reported
that zebra mussel veligers experjenced 100 percent mortality within 11-15 days- at 12-24°C when
there was no food available.
Effect of Water Velocity on Settlement, Attachment, and Feeding
The speed ofwater movement, or velocity, impacts the settlement, attachment and feeding habits
in zebra mussels. Juveniles will settle in internal piping and along any submerged area with a
flow rate of less than 1.5 meters per second (4.92 feet per second) (Claudi and Mackie 1994).
Adult zebra mussels have also been known to avoid high-velocity flow locations and typically
detach from such a poor settlement location and move (e.g., crawl via the foot or float by
detaching the byssal threads) to a more suitable site (Claudi and Mackie 1994).
Ackerman (1999) has shown in laboratory studies that the ability of zebra mussels to clear
plankton can be impacted by water velocity. Increasing ambient velocity up to approximately 10
cm per second led to increased clearance rates, whereas high velocity rates of 20 cm per second
resulted in reduced clearance rates.
IV-11 Review ofZebra Mussel (Dreissel/u po[ymorphu) Species