River clams, also known as freshwater mussels, are bivalve mollusks found in rivers, lakes, and streams worldwide. They are natural filters, constantly processing water in their environment. Their filter-feeding method makes them important components of aquatic ecosystems, contributing to water clarity. Understanding their diet provides insight into their ecological function and sensitivity to environmental changes.
What River Clams Filter From Water
River clams obtain nourishment by filtering microscopic organic particles from the water. Their diet primarily consists of tiny plant-like organisms called phytoplankton, a rich source of nutrients. They also consume zooplankton, small animal-like organisms including various crustaceans.
Beyond living microorganisms, river clams filter detritus, which is decaying organic matter like plant and animal fragments. Bacteria in the water also form part of their diet. These food sources are typically very small, generally less than 200 microns, ensuring efficient capture by the clam’s filtering apparatus.
The Filter-Feeding Process
River clams acquire food by drawing water into their bodies through an incurrent siphon. The water flows over specialized gills, which serve as filtering organs.
The gills are covered with microscopic hair-like structures called cilia. These cilia beat in a coordinated rhythm, creating currents that draw water and trap food particles within a sticky mucus lining the gills. The mucus-bound particles are then transported by the cilia towards the clam’s mouth.
Before ingestion, labial palps sort the collected particles, directing edible material to the mouth. Indigestible particles, such as grit or excess sediment, are wrapped in mucus and expelled from the clam’s mantle cavity as “pseudofeces.” The filtered water and pseudofeces are then expelled through an excurrent siphon. A single freshwater mussel can filter 8 to 15 gallons (approximately 30 to 57 liters) of water daily.
Environmental Influences on Diet
The feeding habits and overall health of river clams are significantly shaped by their surrounding environment. Water quality is a major factor, as clarity, nutrient levels, and pollutants directly affect food availability. High turbidity, caused by suspended particles, can hinder a clam’s ability to filter feed, sometimes causing them to reduce activity or “clam-up.”
Nutrient levels influence the growth of their primary food source, algae. While moderate nutrient levels support a healthy food supply, excessive nutrients can lead to algal blooms and subsequent oxygen depletion, negatively impacting mussel health. River clams are also sensitive to various pollutants, including ammonia, nitrates, and heavy metals. As filter feeders, they accumulate these substances, which can harm their health and survival.
Water flow and temperature also play roles in their diet and well-being. Freshwater mussels require flowing water for efficient filter feeding. Low water flow can lead to stagnant conditions, reduced oxygen, and increased contaminants. Temperature affects metabolic rates and can influence the toxicity of certain pollutants to mussels. A clean aquatic environment provides a consistent supply of varied food particles, important for river clam growth and survival.