Sago pondweed (Potamogeton pectinatus L.): A literature review

Abstract

Sago pondweed ( Potamogeton pectinatus L.) is a submersed macrophyte of nearly cosmopolitan distribution. The plant is of worldwide importance as a waterfowl food but also can be a nuisance in irrigation canals and recreational areas. The plant reproduces by many different means, depending on habitat and environmental stress. Several genetic ecotypes have evolved. Most important as waterfowl food are the turions (tubers), vegetative propagules rich in carbohydrates that are mostly buried in bottom sediments. In temperate wetlands, most turions sprout in spring, making sago behave as an annual. Drupelets (seeds) are the sexual propagules of sago and provide a mechanism for sago to survive periods of drought and excessive water salinity. Drupelets can be washed ashore or carried by birds for long distances. Sago decomposes rapidly at senescence, annually in temperate wetlands. Sago is mostly found in semipermanently or permanently flooded mixosaline lacustrine, palustrine, and riverine wetlands < 2.5 m deep, where fetches are not large or currents are < 1 m/s. Sago seems to prefer stable water levels but can tolerate significant water level fluctuations. Among the Potamogetons, only sago tolerates high salinity, pH, and alkalinity, but it fares poorly among specialist taxa in acidic or nutrient-poor waters. Sago is highly tolerant of eutrophic waters, and it can be the only species of submersed macrophyte present in heavily polluted sites. Sago grows in nearly all bottom substrates. Turbidity is the factor that most frequently limits sago growth. Sago often occurs in monotypic stands but can grow with many other submersed and emergent macrophytes. Dominance by sago in certain wetlands sometimes alternates with dominance by other submersed macrophytes when salinities or other environmental factors change. Sago also can be associated with a large variety of unattached filamentous, planktonic, or epiphytic algae. Increased turbidity caused by planktonic algae often is responsible for lowered sago production. Less common biotic limiting factors are organic pollutants and consumption and uprooting by waterfowl and fish. Sago provides food or shelter for amphibians, reptiles, fish, and mammals. The greatest value of sago in North America is as food for migrant and staging waterfowl, primarily diving ducks and swans. Sago beds also provide habitat for a large complex of invertebrates (an important food source for young waterfowl), but direct consumption of living sago by invertebrates is negligible. Sago has been propagated for many years-indoors, as an experimental organism for work in plant physiology or herbicide testing, and outdoors, for purposes of attracting waterfowl. Much work has also been done developing methods to control excessive sago growth in fishponds and irrigation canals. Future research should concentrate on (1) determining, in a variety of wetland types, the causes of light-limiting turbidity that often suppresses sago growth, (2) understanding the ways in which human activities on and near wetlands affect sago production, and (3) developing reliable and predictable techniques to stimulate sago production for waterfowl by using water level manipulations and other means, in a variety of environmental settings.