American Wildcelery (Vallisneria americana):
Ecological Considerations for Restoration
Value
General
Roots, rhizomes, and stolons of most aquatic plants help to reduce erosion and facilitate colonization by benthic algae and invertebrates; their foliage offers shelter, support and, at least during daylight, a locally enriched oxygen supply (Sculthorpe 1967). Macrophytes also provide a direct or indirect source of food for an immense variety of aquatic invertebrates and fishes, and for birds and mammals that frequent aquatic habitats (Sculthorpe 1967).
Wildlife Food
All parts of V. americana are important food items for many species of waterbirds (Sculthorpe 1967). McAtee (1939) reported that V. americana was eaten by 19 species of wild ducks. Martin and Uhler (1939) examined 7,998 stomachs of 18 species of ducks; V. americana accounted for about 2% of the food eaten, making it the seventh most popular plant food. The plant was the most important food used by ducks in the Lower Detroit River (Hunt 1963). Vallisneria americana and Potamogeton spp. were the most important plant foods as measured by percent volume and the collection of 47 greater scaup (Aythya marila), 44 lesser scaup (A. affinis), and 39 common goldeneye (Bucephala clangula) in the Detroit River during the winters of 1980 and 1981 (Jones and Drobney 1986).
Foods consumed by canvasbacks and food availability were studied on Navigation Pool 7 of the Upper Mississippi River in 1978, 1979, and 1980 (Korschgen et al. 1988). Canvasbacks fed primarily on winter buds of V. americana and consumed 40% of the standing crop of 380,000 (+,-) 44,350 SD kg (dry weight) in Lake Onalaska in 1980. Traditionally, canvasbacks have been primarily obligated to two foods during fall migration -- sago pondweed (Potamogeton pectinatus) and V. americana (Cottam 1939; Perry 1982). The proliferation of V. americana in Navigation Pools 7, 8, and 9 of the Upper Mississippi River (C. E. Korschgen, unpublished data) occurred at the same time that historically important migrational habitats deteriorated elsewhere. During the 1960's and 1970's, canvasbacks shifted their migration routes to respond to the food supplies produced by V. americana on the Upper Mississippi River. An estimated 75% of the canvasback population in the three eastern flyways use this food resource each fall (Korschgen et al. 1988).
Nutritive Value
Shoot Material
The nutritive value of aquatic macrophytes is dependent on the fertility of their water medium. Protein content is usually considered the most valuable constituent of foodstuffs (Boyd and Blackburn 1970). Crude protein (dry weight) has been measured for V. americana from several locations. Proximate analysis of entire shoots collected near Fort Lauderdale, Florida, revealed a crude protein range of 17.6-27.0% of dry weight (Boyd and Blackburn 1970). Plants collected from Lake Mendota, Wisconsin, had 12.4-24.1% crude protein (Schuette and Alder 1927; Gerloff and Krombholz 1966); plants from Lake Chemung, Ontario, had 18.1-19.8% (Muztar et al. 1978a). Donnermeyer (1982) determined the crude protein content of various parts of V. americana over the growing season (Table 7). Levels of various amino acids showed a similar pattern in 12 species of aquatic macrophytes collected from Lake Chemung, Ontario; of the essential amino acids, V. americana had moderate amounts of leucine, arginine, and valine, but was relatively low in lysine (Muztar et al. 1978b).
Mineral and nutrient content of V. americana leaves is similar to that of land forages in the United States (Hentges et al. 1973; Easley and Shirley 1974). Although the nutritive value of dried V. americana was similar to alfalfa hay according to Linn et al. (1975), Muztar et al. (1977) fed dried pelleted V. americana leaves to tame roosters and ducks and determined that it had a true metabolizable energy value of about half that of dehydrated alfalfa. However, the V. americana in the study by Muztar et al. (1977) was not washed before it was dried and surface contamination may have caused excessive amounts of surface ash, therefore a lower true metabolizable energy value. If V. americana is grown in soft water and washed, ash might decrease; V. americana should then have metabolizable energy values comparable to alfalfa and other forage plants (Muztar et al. 1977).
Winter Buds
Winter buds are high in dry matter and low in ash and fiber content, consequently giving them high nutritional potential (Donnermeyer and Smart 1985). Winter buds harvested from September 1980 through April 1981 from Navigation Pool 9 of the Upper Mississippi River contained 10.4% crude protein and averaged 3,978 cal/g dry weight (Donnermeyer and Smart 1985). Vallisneria americana winter buds collected in 1980 from Lake Onalaska Navigation Pool 7 of the Upper Mississippi River had mean caloric contents of 4,075 cal/g dry weight (Korschgen et al. 1988). Winter buds collected from Lake Onalaska in fall 1980 had a mean crude protein value of 11.0%; ash, 4.6%; crude fiber, 2.8%; crude fat, 0.8%; and nitrogen-free extract, 80.8% (C. E. Korschgen, unpublished data).
Invertebrate Cover
A mixed stand of Chara and V. americana in Anchor Bay, Lake St. Clair, Michigan, contained high numbers of amphipods, midge larvae, and other important yellow perch (Perca flavescens) food items (Heberger 1978). When comparing introduced Myriophyllum spicatum beds and mixed native Potamogeton-V. americana communities as habitat for fish and their invertebrate prey in Lake Opinicon, Ontario, five major zoobenthos taxa were found to be 3 to 7 times more abundant in the mixed native communities than in the introduced M. spicatum beds (Keast 1984); significantly more Isopoda, Chironomidae larvae, Ephemeroptera nymphs, Trichoptera larvae, and small gastropods were found in the Potamogeton-V. americana communities in May and July. Densities of foliage invertebrates in May were 4 times as great on combined samples of Potamogeton robbinsii and V. americana than on M. spicatum foliage, twice as great in June, 3 times as great in July, and twice as great in August (Keast 1984). Vallisneria americana had a greater quantity of benthic organisms beneath it than did Elodea canadensis and Najas flexilis; V. americana, with its more extensive root system, may have provided a more stable substrate for the benthos (Gerking 1957).
In a study of Lake Mendota, Wisconsin, Andrews and Hasler (1942) found that V. americana had a smaller standing crop of invertebrates (number/kg dry weight of plant) than did Ceratophyllum demersum, Myriophyllum exalbescens, and Potamogeton pectinatus.
Fish Cover
Eight times as many bluegills (Lepomis macrochirus) and twice as many pumpkinseeds (Lepomis gibbosus) were netted by day in Potamogeton-V. americana mixed communities than in M. spicatum beds (Keast 1984). For bluegills, the ratio was maintained in night collections. Numbers of yellow perch were also higher at night in the mixed native plant communities. In July, 3 to 6 times as many bluegills, pumpkinseeds, and yellow perch were netted, day or night, in the mixed communities. In several Florida lakes, 35 species of juvenile fish inhabited dense aquatic plant communities that included V. americana (Barrett and Schneider 1974).
Other
Submersed aquatic macrophytes serve as important primary producers, using CO2 and inorganic nutrients as raw materials for carbohydrate and protein production. Submerged macrophytes, including V. americana, act as nutrient buffers by using dissolved nitrogen and phosphorus for growth (Stevenson et al. 1979). When these nutrients are removed from the water, they become unavailable for use by algae. Submerged macrophytes also act as nutrient cyclers. Most shoot nutrients are obtained from the sediments through the roots; the nutrients and organic matter leak into the water from living shoots and are liberated during decomposition of dead plant material. Dissolved nutrients and organic matter released to the water may then be transported by currents throughout the water body. In this way, littoral vegetation is a potential source of materials for pelagic production (Carpenter 1981).
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