Northern Prairie Wildlife Research Center
Considerable work has been conducted to develop propagation techniques for some of the subtropical seagrass species such as eelgrass (Zostera marina), shoalgrass (Halodule wrightii), and manatee grass (Syringodium filiforme; Fonseca et al. 1982; Kenworthy et al. 1984). We have summarized methods of harvest, storage, planting, and the labor required for this work.
Depending on the water quality regime, V. americana can probably be best established by transplanting winter buds. Techniques for planting both seeds and winter buds follow.
When establishing V. americana, one must first determine if the planting area is suitable for V. americana growth. For instance, did the area historically have V. americana, and do areas of similar water quality, depth, turbidity, and bottom substrate have V. americana growing in them, or do they support plants with similar habitat requirements such as Potamogeton pectinatus, Heteranthera dubia, Myriophyllum spicatum, or M. exalbescens? Unless conditions appear to be favorable for V. americana, small test plantings should be made the first year.
The area to be planted should have a water depth of 0.7 to 1.8 m with 0.9 to 1.2 m preferred. The most important requirement for sprouting winter buds or seeds is light energy, which is a function of water transparency. Secchi disk readings multiplied by a constant (2.7-3.0) will give the approximate depth of the photic zone required by plants (Cole 1979). Winter buds should be planted so that they will be well within this photic zone. The substrate should be of firm silt or a sand-silt mixture. Hard clay or silty soft mud should be avoided. A slow current is better than stagnant or rapidly flowing water.
Consideration should be given to enclosing the experimental planting area with a fence (wood-slatted snow fence, chicken wire, or welded wire) that will persist in water for several months. Fencing serves several purposes: it protects the young plants from rough fish, acts as a wave break, delimits the planting area, and holds plants that float to the surface at the end of the growing season. A marked but open plot, adjacent to the fenced plot, should be set up as a control planting to see if fencing is needed. Whether fencing is used or not, the planting area should be permanently marked so it can be relocated.
Most studies recommend mixing seeds with wet, sticky mud or clay soil before planting. Pieces of this mixture are then scattered in the planting area, ideally in spring. Muenscher (1936) recommended spring planting over fall planting because seeds planted in fall may be removed from the planting area by water currents, waves, or ice movement during spring breakup; buried by sediment; or eaten by migrating waterfowl. Moyle and Hotchkiss (1945) suggested making balls out of the mud and seed mixture, or placing pieces of it in a single thickness of cheese cloth.
Vallisneria americana fruiting structures containing the seeds can be gathered in late summer with a rake or net (Moyle and Hotchkiss 1945). The harvested fruits can be allowed to decompose in a water-filled container (Muenscher 1936) or broken into pieces (Moyle and Hotchkiss 1945). If planting in the next spring is desired, the seeds or pieces of fruit should be stored in cold water (1-3°C) under dark conditions (Muenscher 1936). Hoover (1984) found that V. americana seeds germinated 2-5 weeks later on the more organic sediments of his study areas. This could be ecologically important because such plants might have competition from other species that are phenologically advanced.
Transplanting Winter Buds
If winter buds are going to be harvested for transplanting, a V. americana bed should be found in the same locale. The size of winter buds is influenced by the pH (acidic conditions produce smaller buds) and the type of substrate (Hoover 1984). Small winter buds produce smaller plants than large buds (Hoover 1984); therefore, more desirable results will be obtained by planting large buds.
Winter buds can be collected by sieving substrate collected from an existing V. americana bed by shovel or with a hydraulic dredge. Winter buds normally float to the water surface when loosened from the sediments. They can then be collected in great numbers with little effort by moving the substrate with a high pressure and volume water pump. We constructed a dredge (pump, dredge, davit) for collecting winter buds (Fig. 5). The gasoline pump had specifications of 8 horsepower and 7.62-cm (3 inches) suction and discharge hoses and an output volume of 83,270 L per hour. The long dredge pipe was 7.62-cm (3 inches) galvanized iron pipe reduced to three 5.08-cm (2 inches) copper nozzles about 15 cm (6 inches) apart. The nozzles (shaped by heating copper tubes with a torch) terminated with 1.27-cm x 7.62-cm openings. The dredge was suspended from the davit by 0.95-cm (3/8 inch) cable. In this way the dredge could easily be moved to any position above the substrate to ensure adequate water pressure for excavating a trench 45 cm wide and about 15 cm deep. The depth of the trench could also be regulated through movement of the boat.
When ready to start excavating, we searched areas that were about 1 m deep (so that persons in chest waders could be in the water). We used a long metal fence post as an anchor for the boat and ran a nylon line from the post through a C-clamp on the bow of the boat. The boat was then moved in an arc with the rope restricting backward but not lateral movement. At the end of the arc a small length of rope was released so that the dredge would excavate a trench parallel to the one made on the previous pass. This technique permitted efficient harvest of an area with the least amount of effort to maneuver the boat.
Two or more persons waded around the boat (or downstream if in a current) and swept up the winter buds with dip nets. In some situations the buds rose to the water surface 30 m or more from the boat so it was best to initially determine the pattern of the water current.
Because winter buds do not store well for extended periods (C. E. Korschgen, unpublished data), they should be collected just before transplanting, and stored in water in a refrigerator (at less than 10° C) to prevent the shoots from elongating.
Muenscher (1936) recommended that winter buds be transplanted in spring for the reasons previously described for seeds. At northern latitudes, the winter buds should be planted from mid-April to early May, when the water temperature is 10-14°C.
An efficient method for planting winter buds is to place one or more winter buds in a reinforced paper envelope in which holes have been punched, or in a cottonpolyester, nylon, or plastic mesh bag (0.64 cm holes) filled with a gravel mixture for weight (Fig. 6). Paper and cotton-polyester bags should be tested in the field to ensure that they will not deteriorate before the winter buds sprout and root. The bags can be prefilled with gravel to avoid delays in the transplanting process. After the winter buds are placed in the bags, the bags should be closed with a twist tie and kept wet until they are deposited at the transplant site.
Trial plantings are recommended for new areas. Success can be determined at minimal cost by establishing two or three paired plots (fenced vs. open) of about 7.5 m on a side. Initially, about 250 to 300 winter buds per exclosure should be planted to determine if the location is suitable. A high-density planting compensates for injured or inferior winter buds that do not grow.
The ideal method for planting V. americana winter buds is to bury them 5 to 10 cm in the sediment. Divers may plant the winter buds by hand, or if water drawdown is possible, the water may be lowered to a level where the winter buds may be planted by hand. Because contracting SCUBA divers is expensing and water drawdown may not be possible, we generally recommend placing the buds in weighted mesh sacks. A planting density of 1,000 per 0.4 ha is recommended.
Records should be kept of how many winter buds were transplanted at each site. The planting should be evaluated during and at the end of the growing season. The simplest way to determine if the winter buds have sprouted and are growing well is to place a couple of the transplant bags that contain winter buds in a sunken container filled with substrate from the site. A float attached to the container helps to locate the plants for periodic inspection. A five-gallon plastic bucket works well if a hole is cut in the side of the bucket to permit water to drain when tbe bucket is lifted.
Leaves will grow rapidly in a favorable environment and, within a few weeks, new rhizomes should irrupt from the primary plant, giving rise to additional plants (Fig. 7). At northern latitudes (Wisconsin) the plants will flower around 1 August, produce winter buds around 1 September, and senesce around 1 October. If the transplant is successful, the plot should contain a dense stand of plants by September (Fig. 8).
In a favorable environment, each winter bud should produce at least three or more new plants. The net gain of plants can be quickly estimated by counting the number of floating rosettes within the fenced area as tbe plants senesce. Careful examination of these rosettes for the descending rhizome, which terminated in a winter bud, will indicate whether or not the plants produced buds. The density and size of the winter buds can be determined by searching for them in the substrate with a post-hole diggger, corer, or long-handled shovel; the number of winter buds per unit area may then be estimated and the size measured.
The planting should be monitored for a second growing season.
Winter buds are available from commercial supply companies that raise and harvest their own stock and cost about $0.10 each. If a trial program or a small-scale operational program is going to be initiated, purchasing winter buds is probably more cost effective than buying the equipment to harvest them (except for long-handled shovels and a sieving box).
In the event that winter buds or seeds are not available from a nearby water body, they can be purchased from wild game food nurseries. Many suppliers sell American wildcelery parts adapted to a northern environment. It is unknown how well these winter buds would tolerate the climate of southern areas or brackish water conditions.