IV. Aquatic plants

ICES mar. Sei. Symp., 194: 106-109. 1992

Impact of Eichhornia and Hydrilla in the United States1

Joseph C. Joyce

Joyce, J. C. 1992. Impact of Eichhornia and Hydrilla in the United States. - ICES mar. Sei. Symp., 194: 106-109.

The history of the introduction of two severe aquatic weed species - the waterhyacinth (Eichhornia crassipes) and hydrilla (Hydrilla verticillata) - is reviewed along with case histories of their economic and environmental impacts. Expensive management programs and regulatory controls have been implemented after introduction and establishment; however, these programs have not stopped the spread of the plants throughout the United States. Future programs must be more aggressive in their attempt to determine weedy potential prior to any purposeful introductions.

Joseph C. Joyce: Center fo r Aquatic Plants, Institute o f Food and Agricultural Sciences, University o f Florida, 7922 N W 71st Street, Gainesville, FL 32606, USA.

Introduction

In a recent article, C. D. K. Cook stated, “There often seems to be an almost blind belief that really trouble­some aquatic weeds have been introduced from else­where and that the main reason for their aggressiveness is that they have been relieved of the ecological re­straints within their native range” (Cook, 1990). Cook further indicated that the cause of the weed problem is invariably man-induced changes to the aquatic habitat which allows the alien species to expand. Cook also estimated that 172 species of aquatic plants have become established outside their native range and that only a few have become seriously troublesome but all are potential weeds (Cook, 1990).

There is no complete agreement within the lake man­agement community over Cook’s statement relative to the problematic nature of these plants being due to man- induced changes. Experience in the United States with two plants in particular, waterhyacinths (Eichhornia crassipes) and hydrilla (Hydrilla verticillata), form the basis for much of this disagreement. These two plants have become serious pests in the United States not due to man’s manipulation of the aquatic habitat but through their growth form, physiology, and reproductive capa­bilities.

1 Florida Agricultural Experiment Stations Journal Series No. N-00381.

History of introduction

The waterhyacinth was introduced into the United States in 1884 at the Cotton States Exposition in New Orleans. The Japanese were distributing the plants as souvenirs, and, as the story goes, the plants were placed in ornamental ponds by the attendees. As the plants filled the ponds, the excess was thrown into nearby creeks and lakes (Barrett, 1989). The introduced plants quickly affected navigation and other water activities in southeastern lakes and rivers. By 1898 the plants had increased to the point that steamboats and other vessels were unable to reach docks or pass through navigation openings in bridges or narrow points on rivers. Public concern over the economic impact of this plant resulted in the passage of the River and Harbor Act of 1899, which authorized the US Army Corps of Engineers to construct and operate vessels and log booms in navig­able waters of Florida and Louisiana in an attempt to manage the impact of the plant. These methods proved inadequate and seasonal climatic conditions provided the only real relief for several decades. The public outcry was so great that agencies resorted to such drastic efforts as spraying the plants with sodium arsenite. This was later prohibited due to the poisoning of applicators and livestock. More scientifically based and environmentally compatible management efforts utilizing safer herbi­cides and host-specific biocontrol insects were eventu­ally developed. Today the waterhyacinth is not a serious pest due to the continuous efforts of many management agencies.

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Another major aquatic plant in the United States, hydrilla, was introduced about 1959 in the Miami and Crystal River areas of Florida. The assumption has been that it was introduced by the aquarium industry as Elodea sp. and was called Florida Elodea for years. Hydrilla quickly became a problem in Florida due to its rapid growth rate and the physiological capability of requiring less sunlight for photosynthesis than native submersed plants. Hydrilla was able to grow in much deeper waters than native species and completely occupy the majority of the submersed habitat of many lakes and rivers. This niche was previously unoccupied by any native aquatic vegetation. This growth character­istic created serious water use, recreation, fish and wildlife and flood control problems which were rarely encountered with native plants.

Impacts of aquatic weeds

An example of the ecological impacts of these two plants is the increased contribution of organic material to lake sediments generated either through natural growth or treatment with herbicides. Table 1 indicates that the amount of organic sedimentation generated by waterhyacinths or hydrilla is greatest when the plants are allowed to completely cover a waterbody and no spray operations are conducted. The more intensive manage­ment activities (<30% coverage) significantly reduces this contribution (Joyce, 1985). Because of this and ecological impacts of these species, many biologists now consider them as “biological pollutants” of our water resources.

There are few disagreements over the impacts of severe infestations of aquatic weeds; however, there are many disagreements and concerns over the management techniques utilized and the magnitude and effects of some of the plant populations. For example, those individuals responsible for ensuring navigation, recrea­tional boating, water recreation, flood control, public health, or irrigation would desire to have as little vege­tation as possible. Whereas, those who are more con­cerned about fish and wildlife values would argue for more vegetation. The main disagreement involves the level of vegetation necessary to support a healthy fish

Table 1. Annual organic sedimentation by aquatic weeds.

Percentcoverage

Tons/acre (dry weight)

Waterhyacinths Hydrilla

0 0.9 0.6<30 1.5 0.9100% (sprayed) 4.2 1.1100% (unsprayed) 6.5 1.3

and wildlife population, while not disrupting native species diversity or interfering with man’s other uses. With exotic plants such as hydrilla and waterhyacinths, which display rapid expansion capabilities, the manage­ment at this “optimum” level becomes difficult and expensive.

Two recent experiences at Lake Okeechobee and Orange Lake, Florida with these two species indicate the magnitude of the problem, the environmental and econ­omic impacts, and the cost of containment.

Lake Okeechobee

Lake Okeechobee, located in South-central Florida, ranks as the second largest freshwater lake in the United States after Lake Michigan. The natural watershed has been highly modified to provide flood control and water supply benefits for agricultural and urban interest, as well as recreation and commercial navigation. In respect to these water resource uses, unmanaged waterhya­cinths have shown the ability to cause severe economic and ecological damage by disruption of these water resource objectives.

As early as 1905, waterhyacinth problems were reported on Lake Okeechobee. Initial control oper­ations consisted of mechanical removal or destruction. These methods were ineffective except on a localized, short-term basis. The development of 2,4-D in 1941, improvements in herbicide application techniques, dis­covery and introduction of biological suppressants (in­sects), and higher levels of funding led to the develop­ment of successful management programs. In today’s management programs, plant populations are aggressi­vely kept below problematic levels. The approach is commonly known as maintenance control.

Table 2 provides an analysis of waterhyacinth control on Lake Okeechobee since 1978 (Bodle, 1990; US Army Corps of Engineers, 1989; Zattau, 1990). Under maintenance control, it can be seen that maintaining the plants at low levels (FY 80-81, 81-82, 88-89, and 89-90) results in lower overall costs, fewer acres sprayed (thus less herbicide used), fewer plants pres­ent, but higher per acre costs. However, waterhyacinth populations on Lake Okeechobee have sometimes been allowed to exceed maintenance control levels when aquatic plant management programs were inter­rupted by the lack of adequate resources (FY 83-84, 84-85), or by policies (FY 86-87, 87-88) that were based upon factors other than many years of oper­ational experience and scientific data. One such situ­ation occurred in 1986 when waterhyacinth manage­ment was halted as a theoretical means to reduce phosphorus concentrations in the lake. In the absence of control programs, waterhyacinth coverage increased by 94% between August and November 1986 and caused emergency conditions on the lake which dis­rupted navigation and water movement, and destroyed

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Table 2. Lake Okeechobee waterhyacinth control expendi­tures and operations Corps of Engineers and South Florida Water Management District 1978-1990.1

Fiscalyear

Total expenditures

($ x 1000)Acres

controlled

Cost ($ per acre)

Acrespresent2

78-79 280.5 8949 31.34 63079-80 330.3 7703 42.88 40080-81 338.1 3509 96.35 N/A81-823 252.3 3306 76.32 69482-83 450.6 8117 55.51 761083-84 638.0 16604 38.42 644984-85 383.5 11995 31.97 126585-86 388.0 6327 61.32 5542486-87 625.4 10 139 61.68 90087-88 715.0 11744 68.88 52588-89 481.7 5256 91.65 5089-90 363.6 4650 78.20 65

1 Data obtained from U.S. Army Corps of Engineers. Jack­sonville, Florida and South Florida Water Management Dis­trict, West Palm Beach, Florida (Bodle, 1990; US Army Corps Eng., 1989; Zattau, 1990).2 Data obtained from annual surveys in August of each year by Florida Department of Natural Resources.3 The SFWMD assumed control operations on the Lake and tributaries from the CO E in June, 1982.4 Acreage reaches record level of 7700 acres in December 1986.

native plant communities. As predicted by previous experience, high costs associated with large amounts of herbicides and manpower (FY 86-87 and 87-88) were necessary to regain maintenance control levels.

O ra n g e L ake

Orange Lake is a 5400-hectare, shallow, eutrophic lake in North-central Florida which undergoes wide annual fluctuations in water level and surface area. The lake is a nationally renowned sportfishing lake and annually attracts a large number of non-local anglers. The lake supports 20 full-time fish camps that provide services such as lodging, guides, boat rentals, tackle, live bait, and food. The lake shoreline is relatively undeveloped and has an extensive littoral area which has historic­ally been covered with spatterdock (Nuphar luteum), maidencane (Panicum hem itomon), knotgrass (Paspali- dium germinatum), coontail (Ceratophyllum demer- sum ), southern naiad (Najas quadalupensis), and blad- derwort (Utricularia sp.) (Colle, et al., 1987). The predominant industry in the immediate area is associ­ated with agriculture (pasture lands) and sportfishing.

Hydrilla was identified in Orange Lake in 1974. Prior to this approximately 2700 hectares of the lake was devoid of submersed aquatic vegetation. Hydrilla was first discovered at a public boat ramp and was probably inadvertently introduced by a boater not removing vege­tation fragments from the boat trailer after leaving an infested lake. Hydrilla quickly increased in coverage

such that by 1977 there was only 114 hectares of open water on the lake or 95% areal coverage by a dense surface mat of hydrilla (Colle, et al., 1987). Hydrilla management activities during this period consisted of chemically and mechanically cutting boating trails from access ramps to the remaining open water areas. In 1978, the hydrilla coverage was drastically reduced due to a dense algal bloom caused by a large influx of surface water. This bloom and the sharp increase in water level drastically reduced hydrilla coverage. During sub­sequent years, hydrilla reinfested the lake from tubers produced by the plants. Due to intense management activities with a new herbicide. Sonar (active ingredient fluridone), hydrilla has not exceeded 70% of the lake area in spite of the water level fluctuations.

Fortunately, the Florida Game and Freshwater Fish Commission periodically conducts non-uniform- probability roving creel surveys on the lake (Pfeiffer, 1967; Ware, et al., 1972) in order to obtain estimates of angler effort. This data, combined with estimates of sportfishing expenditures by resident and non-resident anglers, provided an estimated value of US$1.0 million during the 1978-1979 angling season (Colle, et al., 1987). In 1977, sportfishing activity decreased by over 90% due to the hydrilla infestation, but fully recovered in 1979 after the hydrilla was reduced to low levels. Subsequently, more intensive surveys of economic activity (Milon, et al., 1986; Milon and Welsh, 1989) estimated the total indirect benefit of sportfishing to the region in excess of US$10.0 million. Thus, it can be seen that severe hydrilla infestations which cause significant shifts in sportfishing activities can have severe localized economic impacts.

Regulatory controls

One of the major US points of entry and distribution of aquatic plants is the State of Florida. According to the 1990 Florida Agricultural Statistics Service estimates there are over 44 aquatic plant growers with net sales of over US$7.0 million. In order to avoid intentional intro­ductions of additional potentially harmful species, vari­ous institutional controls, primarily on the aquatic plant importation and aquarium industry, have been enacted. In Florida, laws are in place which regulate the impor­tation, transportation, cultivation, collection, sale, pos­session, and revegetation of aquatic plants. The Florida Department of Natural Resources is charged with devel­oping lists of potentially nuisance species, promulgating rules and permitting procedures for plant culture and possession, inspection of imports and growout facilities, enforcement of violations, and conducting emergency eradication activities upon discovery of nuisance species.

At the national level, the Federal Noxious Weed Act

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of 1974 (Public Law 93-269) regulates the import and movement of noxious weeds under the auspices of the US Department of Agriculture, Animal Plant and Health Inspection Service. This act also lists prohibited nuisance weed species, established quarantine pro­cedures, and specified penalties for violations of US$5000, one year in prison, or both. Unfortunately, proper enforcement of this act was never funded.

Future directions

Prevention of future adverse effects of alien aquatic plant species is similar to that for other plants or animals. Efforts must be intensified to (a) establish systems and mechanisms to provide a predictive capability of poten­tial ecological and economic impacts of species prior to their introduction, and (b) provide a realistic, respon­sive system of enforcement. In the past, the magnitude of the damage was not known until after the species was introduced or released. New advances in tissue culture or bioengineering techniques may provide methods of determining the “weedy” nature of a species or the development of growth characteristics in ornamental species which will decrease their weed potential. Barring such advances, future efforts will require expanded, worldwide databases on the biological and ecological characteristics of potentially weedy species, and past experiences with the target species. The availability of this information and the level of key wording should also be such that those less able to conduct the necessary research will have free and easy access to the infor­mation. Enforcement of international importation and quarantine programs must also be adequately funded so that potentially harmful species are excluded. Further, it is important that these programs be responsive enough that potentially economically important species which

pose limited potential for disruption of native diversityare not unduly restricted or excluded.

References

Barrett, S. C. H. 1989. Water weed invasions. Sei. Am. October, 1989: 90-97.

Bodlc, M. 1990. Personal communication. South Florida Water Management District, W. Palm Beach, FL.

Colic, D. E. et al. 1987. Influence of hydrilla on harvestable sportfish populations, angler use, and angler expenditures at Orange Lake, Florida. N. Am. J. Fish. Manage., 7:410-417.

Cook, C. D. K. 1990. Origin, autecology, and spread of some of the world’s most troublesome aquatic weeds. In Aquatic Weeds. The Ecology and Management of Nuisance Aquatic Vegetation, pp. 31—38. Ed. by A. H. Pieterse and K. J. Murphy. Oxford University Press, New York.

Joyce, 1. C. 1985. Benefits of maintenance control of waterhya­cinths. Aquatics, 7(4): 11-13.

Milon, J. W., Yingling, J ., and Reynolds, J. E. 1986. An economic analysis of the benefits of aquatic weed control in North-central Florida. Food and Resources Economics De­partment Report 113. Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611. 52 pp.

Milon, J. W., and Welsh, R. 1989. An economic analysis of sport fishing and the effects of hydrilla management in Lake County, Florida. Food and Resources Economics Depart­ment Report 118. Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611. 47 pp.

Pfeiffer, P. W. 1967. The results of a non-uniform probability creel survey on a small state-owned lake. Proceedings of the Annual Conference Southeastern Association of Game and Fish Commissioners, 20: 409-412.

US Army Corps of Engineers, Jacksonville District. 1989. FY 1988 Aquatic Plant Control Program District Survey.

Ware, F. J ., Fish, W. V., and Prevatt, L. 1972. Five year creel survey of two Florida lakes. Q. J. Florida Acad. Sei., 35: 31-48.

Zattau, W. Personal communication. 1990. Aquatic Plant Con­trol Costs. US Army Corps of Engineers, PO Box 4970, Jacksonville, Florida 32232.

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