Zebra mussels feed primarily on planktonic algae and zooplankton. Other nutritional sources are bacteria, detritus, and organic mater. When food resources are limiting, intraspecific competition within a zebra mussel population for food can probably be a significant mortality factor and a major density-dependent, population-regulating mechanism. Adult zebra mussels in high-density populations, for example, may compete with their planktonic larvae for limited food resources, thus reducing survival of their planktonic larvae. Strayer et al. (1996) provided evidence that adult zebra mussels outcompeted their pelagic larvae for phytoplankton in the Hudson River and suggested that such food-limited zebra mussel populations may be especially frequent in rivers and estuaries, where ratio of food supply to available substratum is small.
The laboratory investigations of Schneider et al. (1998) indicated that food quality may be a better indicator of environmental conditions suitable for zebra mussel growth than food quantity. Their results suggest, therefore, that the conditions of high suspended inorganic sediment concentrations in large, turbid rivers represent a difficult growth environment for zebra mussels.
Borcherding (1995) reported that the supply of food influenced oocyte development positively, with a high availability of food resulting in significantly larger gonads. Likewise, food is believed to play a role in determining the frequency of zebra mussel spawning (Gist et al. 1997).