1. The Threat of Spread of Zebra Mussel (Dreissena polymorpha) in Maryland, USA
DCL Property Owners Association Meeting
Bruce Michael
Matthew Ashton
Maryland Department of Natural Resources
08/19/2017

2. Why are zebra mussels considered a nuisance/invasive species?
Very fecund – lots of babies!
Easily spread
Outcompete native bivalves
Alter their surroundings
Continue to expand north and westward
Nuisance
Foul and encrust submerged objects
Shells are very sharp
Bioaccumulate toxins in fish and birds
May cause and worsen HABs, dissolved P

3. Where are they in the U.S.?

4. How did they get here?
Ocean going ballast water – initial introduction
New zebra mussel populations more likely from transporting adults than larvae
Adults most often on motors, hulls, trailers or attached to aquatic plants
Docks, buoys, other hard, submerged surfaces
Larvae most often in bilge, live well, or outboard cooling system water
Zebra mussels can live for several days out of water under cool temperature, high humidity conditions
Other AIS can serve as a vector
Waterfowl are not a likely vector

5. What are the effects? – Hudson River
There are no simple answers to how an ecosystem may change from AIS.
Perception of + vs. – change may vary by management goals.
For example, more light is good, but more phosphorus is bad.
With zebra mussels, there is a prevailing misconception of clear vs. clean water – they “cleaned up the Great Lakes”.
Adapted from Strayer (2009) Front Ecol Envi, p 137

6. Slow creep towards Maryland
2015
2009
Mid-Atlantic risk assessment studies
Multiple ZM observations in Middle, Gunpowder, and Bush River estuaries
PBAPS veliger monitoring begins
Introduction to Great Lakes
1988
2010
???
Introduction to Susquehanna at Binghamton, NY
ZM found below Conowingo Dam
2017
ZM found during launch at DCL
1991
2016
First record in Maryland at Conowingo Dam
ZM found during launch at DCL
ZM found on buoy anchors at Havre de Grace, MD
2008
ZM found on more anchors in higher numbers
Scale is NOT linear
2010
2014

7. Zebra mussel threat: ISMT 2009 Habitat Suitability Map
Let’s talk about this map as it has been taken by some to mean things that are not entirely accurate

8. What are major management tools for AIS?
Status quo
Reactive approach, when possible mitigate impacts following establishment, conduct informal monitoring, etc.
Increase education/awareness
Effectiveness of approach in preventing or slowing spread?
Proactive management
Inspection and decontamination (departing v. arriving?)
Early detection, next generation monitoring (eDNA)
Legislative or regulatory
DNR uses examples of all of these tools when appropriate or available.
Some are better than others at slowing spread or preventing introduction.
Physical and financial requirements vary.

9. Zebra mussels are a statewide issue
AIS is an issue for all waters, but threats vary by species and locality.
Recreation is rarely the primary use of an impoundment
Zebra mussel relative risk varies over space, time, and environment.
Greater risk is posed to water bodies with public and industrial water supplies
Preventing IS introductions should focus on disrupting pathways that allow introduction to happen instead of single species

10. Questions