The invasion of zebra mussels into North America marked a turning point in public policy and concerns addressed by environmental activists. Prior to the introduction of the mussels in 1988, there was limited interest by natural resource managers in the topic and no laws in place to prevent these invasion incidents. Now aquatic nuisance species are a major subject of research and biological invasions are thought to be a major cause of extinction.Boaters should be familiar with the common terms and phrases used in discussing aquatic invasive species.
Introduction of Zebra Mussels - By the early 1800's, zebra mussels were found in all the major river drainages of Europe. The introduction of the invasive species to the Great Lakes in 1988 is believed to been caused by the exchange of ballast waster from a cargo ship sailing from the Caspian Sea. The first infestation was identified in Lake St. Clair and within two years, the mollusks had spread to all of the Great Lakes. Zebra mussels escaped the Great Lakes and entered the waters of the Illinois and Hudson Rivers. These rivers connect to the Mississippi River and by 2005, zebra mussels could be found as far south as Louisiana. In the beginning of 2007, it was reported that the mussels could be found in Lake Mead, Nevada. Zebra mussels are found now in at least 20 states and 2 provinces.
Physical Appearance - Zebra mussels are small shellfish (50 mm/2 inches long) identified by the unique striped pattern on their shells. The mussels attach themselves to the surfaces of objects in contact with the water. This is accomplished through the use of sticky byssal thread extruded by the mollusks. Zebras have a lifespan of about four years.
Damage Caused By Zebra Mussels - Zebra mussels are filter feeders, passing up to a liter of water a day through their bodies to capture phytoplankton. Phytoplanktons are the foundation of lake and river ecosystems, the primary food supply for fish and other aquatic species. An invasion of the mussels will greatly reduce available plankton biomass and thus put native animal species at risk for lack of food. Zebra mussels cause biofouling by forming massive colonies in water inlet pipes. Clogged pipes suffer reduced performance and must be cleaned to remove the infestation. Water inlets serve fire service pumps, irrigation pumps, public water systems, industrial heat exchangers, power plant cooling systems and related equipment. It is estimated that $250 million is spent each year in just the Great Lakes region to mitigate this problem. Accumulations of zebra mussels can damage waterfront infrastructure like docks and piling. Boat hull performance drops rapidly from the drag effects of attached mussels.
How Do They Spread - Zebra mussels are unique in that they can be transported during any stage of their life cycle. The mollusks reproduce after their first year of life. Spawning occurs anytime the water temperature is above 20°C (68°F). A single zebra mussel can lay millions of eggs that develop into free floating planktonic larva known as veligers. Veligers can not be seen by the unaided eye and drift throughout the water column. Boaters can accidentally transport zebra mussels by contamination of bilges with veligers or adult zebras attached to the hull. Adult zebra mussels can survive several days out of the water. Researchers documented the crossing of trailered boats into California infested with the mollusks.
Control Measures - Boaters can help slow the spread of zebra mussels through good vessel management practices. Once introduced into the wild, these animals cannot be controlled. Drain all water from your boat's bilges, bait wells and live wells at the launch ramp. Inspect your boat hull for mussel infestations. Wash the boat and trailer with hot water or let them sit for five days before moving out of the immediate area. Avoid taking fish, bait or plants from one area to another.
