Zebra Mussels: A Destructive Marine Invasive Species
Invasive species are a growing concern to natural ecosystems and a large disruptor to native species. They are categorized by two characteristics; being a non-native species and causing harm to the environment, economy, or human health . Therefore not all non-native species are invasive, but all invasive species are non-native. According to The National Wildlife Federation, invasive species are considered a leading threat to indigenous wildlife and are responsible for approximately 42 percent of threatened and endangered species. A prime example of a marine invasive species in the United States is zebra mussels. These species are from the opposite side of the world and negatively impact the health of the lake ecosystem, as well as the economy in the region.
Zebra mussels are a small mollusk named for the dark lines stripping across that resemble a zebra’s pattern. Native to the Eurasian region and originating from the Caspian sea and Ural river, they reside in fresh and brackish bodies of water. The earliest sightings of these mollusks in the United States was in the Great Lakes and surrounding estuaries in 1988. They have now been found in thirty more states’ fresh water systems.
The transfer of invasive species is generally through human activity. In this case the vector is thought to be through large ships’ exchange of ballast water. Ships traveling from Europe to the United States in the eighties would intake water to their ballast for stability purposes and then the water was released at different locations to maintain the ship’s balance. This water can host a multitude of aquatic organisms making it a common transmitter of invasive species. There are now greater regulations surrounding ballast water treatment and release in order to prevent more cases of invasive species such as the zebra mussels.
Once the mussels were released into the Great Lake region, the expansion of the species was rapid and devastating. The zebra mussels are extremely resilient due to fast reproduction rates, dense accumulation, and efficient feeding methods. The species have a relatively short lifespan, only living about two to five years. Female mussels will begin to rapidly reproduce at around two years old by releasing upwards of a million eggs every year until they die. After starting off at a microscopic stage they will grow to be about 50 millimeters in length at adulthood. These adult mussels will cluster on hard surfaces such as rocks, boat hulls, propellers, and docks by the hundreds and thousands. Zebra mussels are also considered filter feeders. This means that they are constantly intaking water and removing plankton and other organic particles from their surroundings.
These characteristics contribute to extensive negative impacts on the surrounding environment and local economies. An exponential growth in this invasive species will overwhelm native organisms either forcing them to relocate or overtaking them all together. Zebra mussels will attach themselves onto anything in sight, including other mussels. This trend prevents the existing mussel population from functioning normally by inhibiting feeding habits and movement. Their intensive feeding methods can completely remove the main food source for other mollusks and small marine organisms. The loss of native species has a negative impact on the entire food web in the region which can create ripple effects throughout an ecosystem. Additionally, the loss of indigenous mollusks can impact water quality, due to the mussels ability to regulate water clarity and purity. Local economies are impacted by the loss of species and disruption of food webs if they are reliant on commercial fishing or environmental tourism connected to the body of water. Another economic impact is through biofouling. This refers to the accumulation of organisms on man-made surfaces. Zebra mussels are a textbook example of this process by attaching to any man-made surface that is left in the water for an extended period of time. All boat’s motors, propellers, intake pipes, and general machinery are subject to exposure to the mussels at their microscopic stage. As the mussels grow inside a vessel they can cause extensive and irreparable damage to boats as well as being difficult to clean or remove from surfaces.
The best way to avoid the threat of zebra mussels is to prevent them from entering a body of water in the first place. Removal of this species is extremely difficult which is why the zebra mussels have been able to spread to the wide reaches of the United States from their humble beginnings in the Great Lakes. Preventing further spread on boats is already occurring through governmental regulations regarding ballast water spread. There are options to release ballast water in the open ocean where smaller organisms are less likely to survive, as well as on-board treatment of ballast water that will remove harmful organisms and particles prior to release. This can also be done on a local scale by requiring that private boats thoroughly clean every crevice of their boat that is in the water before entering a new body of water. The monitoring of zebra mussels and increased education about them will also help communities manage the spread of this invasive species and prevent further harm.
Sources: Marine Insight, National Wildlife Federation, United States Geological Survey