Protecting Boats and Motors From Zebra Mussels The title of this presentation is “Protecting Boats and Motors from Zebra Mussels.” 1

When zebra mussels arrived in North America from Europe in the late 1980s, Great Lakes boaters soon learned that their boat hulls and submerged engine parts could become rapidly encrusted with the mussels. 2

VELIGER 3 That’s because of the unique biology of the mussel.   Each adult female zebra mussel can produce over one million eggs per year. Not all of these eggs survive, but those that do survive become veligers—the zebra mussel’s free-swimming, microscopic larval stage. Veligers grow into the mature stage. It is at this point that they firmly attach to mostly hard surfaces with a tuft of filaments called byssal threads. Great Lakes researchers have found that veligers can settle onto hard surfaces within a few hours especially under calm water conditions. 3

Veliger settlement peaks in mid-late summer Settlement continues through autumn The free-swimming veligers may be present in the water throughout the boating season, reaching peak settlement in mid or late summer.   Further settlement occurs in early autumn as hatching continues and small juveniles detach, drift through the water, then settle and re-attach onto new surfaces. 4

If conditions are right, large populations of mussels can form and lead to heavy infestations. This dock post was submerged in a Lake Erie harbor for only two seasons, but is completely infested with zebra mussels. 5

In heavily infested waters, zebra mussels can form thick masses not only on underwater structures, but also on boats and engines.   Zebra mussels can attach firmly to fiberglass, aluminum, wood, and steel boat hulls in quantities that can decrease boat performance and damage the hull finish. Attached mussels can also hitchhike on these boats to other water bodies. This steel boat hull was painted with an antifouling bottom paint on a two-foot section just below the waterline, while the lower hull was not painted. About seven bushels of zebra mussels accumulated on the unprotected portion during one summer, and completely clogged the cooling water intakes. 6

The lower units of outboard and stern drive engines can also become encrusted with zebra mussels—on both the outer surfaces and inside the housing as far up as the pump impeller.   Water intakes, located on the lower unit housing or in the propeller hub, are entry points for zebra mussel veligers and juveniles. 7

Inhibit Zebra Mussel Attachment Expose boat hulls to high water velocity Run engines frequently to kill veligers Raise lower units out of water Use boat lift Treat boat hulls and lower units with antifouling coatings Boat owners can reduce the impact of zebra mussels, and thereby save money on costly removal and repairs, by inhibiting zebra mussel attachment. This can be done in a number of ways.   Boaters can make sure to operate their craft frequently. Weekly exposure of boat hulls to high water velocity can minimize zebra mussel attachment. Engine heat can kill larval mussels, so running the engine can protect parts above the pump impeller. Outboard and stern-drive engines can be left with the lower units raised, thus avoiding contact with mussel-infested water. Likewise, boat lifts can protect all boating equipment by reducing contact with infested water. And finally, boat hulls and engines can be protected with the use of antifouling coatings. 8

Antifouling Coatings Use of antifouling coatings to inhibit algae and other marine organisms is a long-standing practice for boats left in the water for extended periods. The active ingredient in most antifouling paints is either copper or tributyltin, also known as TBT. 9

Copper-based Paints Effective antifoulants Generally available over-the-counter Effective on fiberglass, wood, and steel Not recommended for aluminum Boat bottom paints containing particles of copper or copper oxide are effective antifoulants and …   Are available over the counter in most states. They are labeled for application on fiberglass, wood, and steel. However, copper is a very reactive metal that can rapidly erode aluminum through electrolysis. On aluminum boats, this may cause rivets to fail or result in pitting of the hull. Therefore, its use on aluminum boats is not recommended. 10

Tributyltin (TBT)-based Paints Effective antifoulants Highly toxic Require a pesticide applicator permit Use primarily on aluminum boats While a tar-based undercoating may help protect an aluminum surface from copper paints, aluminum boats in many states are protected with TBT-based paints, which are not reactive with aluminum.   TBT is an effective antifoulant… but is highly toxic. Paints containing TBT are classified under federal regulations as restricted-use pesticides. These regulations require a pesticide applicator permit from the state to purchase or apply TBT-based paints. Some states have further regulations restricting the use of TBT. TBT-based paints are labeled for use only on aluminum boats, on other kinds of boats over 25 meters in length, and on submerged aluminum motor parts. 11

Comparison of Antifouling Coatings Copper-based paints – season-long deterrence TBT-based paints – season-long deterrence Antifouling engine sprays with TBT – 10 weeks Oil-based coating – no measurable protection Evaluations of bottom paints conducted at Lake Erie by Ohio Sea Grant Extension in 1990 demonstrated that commercially available antifouling coatings could provide season-long zebra mussel protection in temperate climates. Among the findings were that:   Copper-based and TBT-based paints provided season-long deterrence to zebra mussels; Antifouling engine sprays containing TBT provided deterrence for at least 10 weeks; And a popular oil-based antifouling coating exhibited no measurable protection against zebra mussel settlement. 12

CAUTION Use paints that release active ingredients only when they’re submerged One word of caution…   Some antifouling paints continue to release active ingredients even while out of the water. It’s best to use paints that release protective chemicals only when they’re submerged. Ask your marine dealer for recommendations. 13

Application of Antifouling Coatings Apply in spring prior to launching Use tar-based undercoating to improve boat performance Revitalize intact coatings Antifouling bottom paints should be applied in the spring prior to launching.   Before applying antifouling paint to a fiberglass hull, it’s best to first sand the hull and then apply a tar-based undercoating. This undercoating can impede water absorption through the gel coat and can improve boat performance. Intact coatings of previously applied antifouling paint can often be revitalized by retouching bare spots and by buffing the paint with fine steel wool or coarse burlap to expose the active ingredients. 14

Protect engines, too! Antifouling paint In-line strainers 15 Where TBT-based paints are permitted, aluminum parts of outboard or stern drive lower units may be cleaned and sprayed with a labeled, TBT antifouling engine paint. The housing should be removed and the inner surfaces sprayed as far up as the pump impeller.   Inboard engines can be partly protected by painting as far as possible into cooling water intakes with the appropriate antifouling paint. Some marine service departments further protect engines from zebra mussels by installing in-line strainers for cooling water. Ask your marine service manager for a recommendation on the proper strainer for your boat. Boats and engine parts protected by antifouling coatings may still develop a thin layer of microscopic organisms known as a “biofilm” after many weeks in the water, but zebra mussels haven’t been known to attach to fresh, intact, antifouling paint. Protect engines, too! Antifouling paint In-line strainers 15

CAUTION Before using any antifouling coating, check about local regulations. Before using any antifouling coating, check with your marine dealer or state natural resource agency about local regulations. 16

Remember……. Remember, antifouling paints can prevent zebra mussels and their larvae from attaching to your boat or motor, but other equipment may still provide pathways for mussels and other exotic species to travel from one water body to another. Here’s what you can do to stop them: 17

Check boat or engine parts that aren’t normally painted Check boat or engine parts that aren’t normally painted. If you see mussels or feel gritty particles that could be tiny juveniles, clean them thoroughly.   18

Also Be Sure To….. Check marine toilet outflows Check drain plugs Check bait well and live well inflows and outflows Wash down intakes Also be sure to:   Check marine toilet outflows… Check drain plugs… Check bait well and live well inflows and outflows… And wash down intakes… 19

Help Slow the Spread In addition, before leaving the boat launching area, take the following actions: 20

Remove all aquatic plants and animals from the boat, motor, and trailer. Remove all aquatic plants and animals that may be clinging to the boat, motor, and trailer. 21

Check anchors and other equipment for mud or plants. 22

Drain lake or river water from bait bucket, livewell, and bilge. 23

Dispose of unwanted bait on shore or in the trash. Never dump unused live bait back into the water. 24

Rinse boat and equipment with high-pressure or 104 degree F water, especially if moored for more than a day. Rinse boats, motors, and other potentially contaminated equipment with high-pressure or 104 degree Fahrenheit water, especially if moored for more than a day. 25

OR, Dry all equipment for at least 5 days under good drying conditions. 26

Written and Produced By: Fred L Written and Produced By: Fred L. Snyder District Specialist, Sea Grant Ohio State University Extension 7/2000 All Rights Reserved Photo Credits: slides 1, 2, 4, 5, 6,8, 10, 11 - Fred L.Snyder, Ohio Sea Grant Extension slide 3 - Gordon Hopkins - Ontario Ministry of the Environment slides 4, 7, 9 - Steve Krynock, Drawbridge Marina, Port Clinton, Ohio Sponsored by Ohio Sea Grant , NOAA grant NA86RG0053 27