The Quagga mussel (Dreissena rostriformis bugensis) is a freshwater bivalve mollusk and a globally recognized invasive species. Originating in the Dnieper River drainage of Ukraine, this small mussel has spread rapidly across Europe and North America, including the Great Lakes, primarily via transoceanic shipping ballast water. As a highly efficient filter feeder, its massive populations dramatically alter the aquatic environments it colonizes. Understanding its feeding mechanics and diet is necessary to comprehend the widespread ecological changes it causes.
The Mechanism of Feeding
The Quagga mussel employs filter feeding to obtain sustenance from the water column. Water is drawn into the shell cavity using tiny, hair-like structures called cilia, which create a current pulling water through an incurrent siphon. Inside the mantle cavity, the mussel’s gills remove suspended particulate matter, which is then transported to the mouth for ingestion.
Filtered water and unconsumed particles are discharged back into the environment. Particle-free water exits through the excurrent siphon. A single adult Quagga mussel can filter a liter or more of water daily, a high rate compounded by the dense colonies they form.
The filtration rate is influenced by external factors, including water temperature and flow velocity. Filtration decreases significantly below 7.5°C but is highest in warmer water between 12°C and 24°C. The ability of the Quagga mussel to maintain a high feeding rate across varying conditions is a major factor in its success as an invasive species.
Primary Food Sources
The primary diet consists of microscopic particles suspended in the water column, collectively known as seston. Seston includes living organisms like phytoplankton and zooplankton, non-living organic detritus, and bacteria. Phytoplankton, the microscopic plants at the base of the aquatic food web, constitute a substantial portion of the ingested material.
The mussel is a selective feeder, sorting particles to choose which ones to consume and which to reject. Maximum clearance rates occur for particles between approximately 5 and 35 micrometers in diameter. This pre-ingestive selection process allows the mussel to bind undesirable or toxic particles with mucus, forming a non-ingested waste material called pseudofeces, which is then ejected.
The ability to reject low-quality food, such as toxic cyanobacteria often associated with harmful algal blooms, gives the Quagga mussel an advantage over native filter feeders. The rejected materials are deposited on the lake or river bottom, distinguishing them from true feces. This efficient, selective feeding allows the mussel to thrive on food sources that native species cannot utilize as effectively.
Ecological Impact of Their Diet
The Quagga mussel’s immense filtering capacity fundamentally changes the physical and biological characteristics of the water body. By removing large quantities of suspended particles, especially phytoplankton, the mussels dramatically increase water clarity. This increased clarity allows sunlight to penetrate deeper, stimulating the growth of aquatic plants at greater depths.
The removal of phytoplankton from the open water disrupts the base of the native food web, creating a trophic cascade. Native fish and invertebrates, such as zooplankton, rely on this plankton and experience a significant decline in available sustenance. This shift can negatively affect native fisheries dependent on these small organisms.
The production of pseudofeces also has significant consequences for the ecosystem. As these waste particles accumulate on the bottom, they release nutrients and can promote the growth of nuisance algae. Furthermore, the mussels accumulate organic pollutants and heavy metals in their tissues at concentrations up to 300,000 times greater than in the surrounding water, exposing predators to high levels of these contaminants.