Unionid feeding strategies

摘要

The continued decline of many unionid communities throughout North America has been attributed to many factors ranging from pollution to exotic species. However, one main factor, food supplies, is rarely discussed. This raises a question: are populations declining in some locations because critical food supplies are no longer present? A review of the current research on unionid feeding highlights our limited knowledge about dietary requirements. Feeding studies on wild populations have been limited because of the difficulties in separating assimilation from ingestion in filter-feeding organisms. Recent technological advances such as stable isotopes and C super(14) enrichment have provided some information on food selectivity and have shown that unionids feed on a wide range of items including algae, dissolved organic molecules and bacteria. But these studies have not detected any food resource partitioning between sympatric genera or species. All species, regardless of shell length, type of gill cirri, siphon structure, or physical location in the substrate, appear to feed on particles <29 microns and can obtain food from either planktonic or benthic sources. However, such apparent omnivory does not translate into easily-maintained adults under captive conditions. Without access to natural food supplies, adult unionids rarely thrive. Dietary supplements such as used for marine bivalves do not support adult survival, though larvae can be reared using marine algae. Apparent omnivory is obviously misleading regarding actual dietary needs. In-depth surveys of potential food resources in waters with healthy unionid populations are critically needed to understand the relationship between food resources, unionid feeding strategies, and long-term survival.