Zebra mussels are very efficient filter feeders. Their gills remove particles from water as it circulates through the mantle cavity (the internal space enveloped by the mantle). The mantle forms two openings called the inhalant and exhalant siphons (Barnes 1968). The inhalant siphon (the largest of the two openings) can have 80 to 100 tentacles, which assist in the selection of food entering the mantle cavity. Cilia on the labial palps of the gills sort particles transferred to them by the food grooves and move particles that are of appropriate size and palatability to the mouth. Rejected particles are bound in mucus and moved to the edge of the mantle. Rapid closing of the shell valves expels the mucous-bound particle strings, referred to as pseudofeces, out of the mussel through the inhalant siphon.
The siphon is normally used for the intake of water and nutrients, but also assists in this important function of cleaning the gills of unwanted materials.
Water that has been filtered by the zebra mussel is almost free of suspended matter (Lvova 1977). Filtered particles that are not ingested are deposited on the bottom as pseudofeces and postdigested materials are deposited as feces. The deposition of large amounts of seston significantly improves the food base for many benthic animals. The zebra mussel shifts material from the pelagic to the benthos by transporting matter from the water column to the benthic community. This movement of seston from the water column to the benthos can induce large changes in all aspects of aquatic ecosystems (Karatayev et al. 1997, Strayer 1999).
The accumulation of large quantities of zebra mussel pseudofeces is capable of affecting water chemistry and creating a foul environment for other aquatic organisms. In the benthic community, however, other macroinvertebrates use pseudofeces as food (see Impacts on the Benthic Trophic Structure).
Impacts on the Benthic Community