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

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

Where are they in the U.S.?

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

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

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

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

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.

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

Questions