Zebra mussels (Dreissena polymorpha) are freshwater bivalves that originated in the Black and Caspian Sea regions of Eurasia. They were inadvertently introduced to North American waterways in the late 1980s, where they rapidly spread and established dense populations. These mussels are widely recognized for the significant ecological and economic challenges they present, including disrupting native ecosystems and clogging infrastructure. Despite their invasive nature, their unique biological characteristics prompt exploration into hypothetical applications that might leverage their functions for lake system improvement.
Zebra Mussels’ Filtering Power
Zebra mussels are highly efficient filter feeders, processing large volumes of water. They draw water into their bodies through an inhalant siphon, where microscopic particles are filtered out by their gills. This process involves consuming phytoplankton, small zooplankton, bacteria, and various organic debris from the water column. An individual adult zebra mussel can filter approximately 1 to 10 liters of water daily depending on conditions.
Particles deemed unsuitable for consumption are combined with mucus and expelled as pseudofeces, which are then deposited onto the lakebed. This allows them to process vast quantities of water. Given their ability to form dense colonies, sometimes reaching up to 700,000 individuals per square meter, the collective filtering capacity of a large population is substantial. This continuous filtration significantly impacts the water chemistry and particulate matter within infested aquatic environments.
Enhancing Lake Water Clarity
The extensive filtering activity of zebra mussels has a direct and noticeable consequence on lake water quality, observed as increased water clarity. By removing suspended particles, including phytoplankton and other microscopic organisms, these mussels can improve water transparency. For instance, Lake Erie experienced an increase in water clarity from 6 inches to approximately 3 feet in some areas following the establishment of zebra mussel populations. Similarly, clarity in Lake Erie and Lake St. Clair increased by 85% and 50% respectively.
This enhanced water clarity allows sunlight to penetrate deeper into the water column, which can promote the growth of submerged aquatic vegetation. While this might appear beneficial, it can also disrupt the natural balance of food webs by reducing the primary food source for native zooplankton and fish. Furthermore, zebra mussels can selectively reject certain types of harmful cyanobacteria, potentially leading to an increase in toxic algal blooms by consuming their competitors. Their presence also influences nutrient cycling, altering the fluxes of phosphorus and nitrogen between the water column and sediments through sequestration in their biomass and subsequent release upon excretion or decomposition.
As Biological Monitors
Zebra mussels show potential as biological monitors for detecting pollutants in aquatic systems. Their high filtration rates mean they process a large volume of water, leading to the accumulation of various substances within their tissues. This includes organic pollutants like polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and dichlorodiphenyltrichloroethane (DDT), which can be bioaccumulated at levels up to 300,000 times higher than ambient water concentrations.
Zebra mussels also accumulate heavy metals like cadmium, lead, chromium, mercury, arsenic, and zinc in their soft tissues. Analyzing the concentrations of these contaminants in mussel tissues can provide insights into environmental contamination levels and track changes in water quality over time. Their sessile nature and wide distribution make them suitable “sentinel species” for pinpointing pollution sources and assessing the effectiveness of remediation efforts in specific areas.