sign in sign up
<<
Home , Hydrilla

Hydrilla Verticillata

Fish 423, Fall 2011

Aquatic Invasion Ecology

Logan Spencer

Diagnostic Information

Hydrilla verticillata is most commonly known as Hydrilla but also known as Water Thyme, , Indian Star Vine, and Wasserquirl. It belongs to the Kingdom Plantae, Phylum Magnoliophyta, Class Liliopsida, Order Hydrocharitales, Family ,

Genus Hydrilla, and Species Verticillata. Figure 1. Photo of Hydrilla in the water forming a mat (left). Close up photo of Hydrilla (right). Basic Identification which are located in a whorl pattern (Blackburn Hydrilla is an aquatic invasive perennial and Weldon). There are also white that species with long slender stems. It can be form that float on the surface water. found in freshwater such as lakes, Hydrilla has an appearance that is very similar to rivers, ponds, canals, springs, streams, reservoirs that of the native , the American and even ditches. The roots of hydrilla are long Elodea (), and the non native and slender usually found buried in the sediment Brazilian Elodea () (Boersma et al. being a white to light brown in color. At the end 2006). These species can be easily confused of the roots the tubers form which are compact with one another but there are differences to tell buds that are buried in the sediment. Long them apart. Noticeable differences are that the slender stems grow through the sediment and flowers on the Elodea and Egeria are larger than can reach a length of 8.5 meters at a growth rate those on hydrilla and that hydrilla has a texture up to approximately 2 centimeters a day (MA that is more rough (Boersma et al. 2006). One Dept. of Cnsv.). The stems branch out when major difference between the is that they reach the water surface and bend hydrilla produces tubers while the other two horizontally to form large dense mats which can species do not (Boersma et al. 2006). contribute to approximately 20% of the plant’s total biomass (Columbia Uni.). The are Life-history and basic ecology narrow and green with a reddish mid-vein underneath. The margins are visibly serrated and Life cycle the underside of each has a small spine. The Hydrilla can sprout very easily. A new leaves are approximately 1-2 centimeters in plant can form from as little as a stem fragment length and there are usually 4-8 leaves per node with just a single node attached (IN Dept. of Figure 2. A drawn depiction of Hydrilla Verticillata showing the entire plant including the tuber, a leaf, the female , the male flower, and the turion.

Figure 3. Drawn depiction of the three aquatic plants to help present the differences. Hydrilla on the left has 4-8 leaves per node. Elodea (American Elodea) in the middle has three leaves per node. Egeria (Brazilian Elodea) on the right has longer leaves and 5-6 leaves per node. NR.). It can also sprout from just fragments of Nitrogen, Potassium, and Phosphorus to grow. the tubers, turions and seeds. Tubers are It can store nutrients and use them at later times approximately 5-10 mm long and are white to to help compensate for when it is limiting yellowish in color (IN Dept. of NR.). The tubers (Barko et al. 1988). of hydrilla are formed on the stem beneath the sediment and each stem can produce up to 6000 Reproductive strategies new tubers (MA Dept. of Cnsv.). The tubers can There are two biotypes of hydrilla; monoecious survive out of the water for several days and and dioecious (Steward and Van 1987). The even lie dormant for approximately 4 years in dioecious plants have only the male or female the soil before sprouting a new plant (Langeland flower per plant and the monoecious plants have 1996). The turions are formed in the leaf axils. the flowers of both sexes on a given plant They break off from the plant and move toward (Boersma et al. 2006). Hydrilla has four the sediment and once it is there it can sprout a different ways of reproducing making it new plant. Turions are green compact buds that extremely successful as an . are approximately 5-8 mm in length and are The four different ways of reproducing are produced in the leaf axils in the dioecious plants fragmentation, turions, tubers, and seed. Both and on the stem tips in the monoecious plants biotypes of Hydrilla produce turions and tubers (IN dept. of NR.). Seeds can be ingested by and usually create them during fall as birds and if excreted into freshwater habitats can overwintering structures. The monoecious sprout as well. plants put more energy into tuber and turion Once grown hydrilla then becomes intertwined productions then the dioecious plants do (Sutton with other hydrilla plants to form a mat across et al. 1992). the surface of the water which blocks the The monoecious plants produce female flowers sunlight from other plant species. Hydrilla then that have three petals about 10-50 millimeters in keeps spreading until either eradicated or it takes length and 4-8 millimeters wide (WA Dept. of complete domination of the body of water. Eco.). They grow attached to the leaf axils and float on the water surface. The male flowers Feeding habits have three whitish to reddish petals that are Like most all plant species Hydrilla about 2 millimeters long and three sepals that utilizes sunlight and nutrients to survive. This are about 3 millimeters long and 2 mm species however can thrive off little sunlight and wide(WA Dept. of Eco.). The also form on the limiting nutrients. The sunlight levels needed to leaf axils but break off and float on the surface survive are much lower than those of other plant water. The male flowers expel the pollen while species. It also utilizes such nutrients as Carbon, floating on the surface and the females become pollenated. In North America all dioecious plants are female and in Washington the plants were all monoecious (IN Dept. of NR).

Environmental optima and tolerances Hydrilla is considered the one of the most threatening invasive species to the . It can tolerate many various conditions because it has adaptations which allow it to outcompete many other plant species. It can grow at low Figure 4. A map showing the locations and biotypes light intensities which allow it to grow for of Hydrilla distributed across the United States. longer periods of the day and at deeper depths. (Madeira et al. 2000).

It can absorb Carbon from the water more on every continent in the world except efficiently allowing it to thrive during summer Antarctica. Within the United States it has months when Carbon can become a limiting spread across the Eastern states. The nutrient (Langeland 1996). It can store nutrients monoecious plants have dominated the for later use in case that nutrient becomes Southeastern states while the dioecious plants limiting and it can tolerate various water have dominated the upper Eastern states. Both conditions including salinity levels of up to 9-10 biotypes of hydrilla have also spread throughout parts per thousand (Langelanf d 1996). . In the Pacific Northwest the only documented spotting of Hydrilla was located in Biotic associations (pathogens, parasites, and Washington State. It was spotted in Pipe Lake commensals) and Lake Lucerne. There has only been one biotic association connected with hydrilla. The mats that are formed by hydrilla have been reported to be a great for (blue-green algae) which produce a dangerous toxin for the wildlife (Menninger).

Current geographic distribution

Figure 5. A 2003 aerial view of the Hydrilla locations Hydrilla is thought to be native to Australia, within Washington State showing Pipe Lake (left) and Asia, and parts of Africa. It is currently located Lake Lucerne (right). (WA dept. of Eco.) History of invasiveness purchased under the wrong name. Another of which is by hitchhiking on the water lily (WA Hydrilla is believed to be first introduced into dept. of Eco.). The water lily was placed in the The United States in the 1950’s. It was first lake and it is believed that it was possible that a observed in Florida. Because of its adaption to fragment of hydrilla tagged along and then survive in many conditions it easily establishes became introduced. Luckily because the Lakes and spreads once it is introduced. In the Pacific have no boat launches the hydrilla problem was Northwest it has only been sighted in two lakes able to be contained to this area and treated. that are joined. Factors influencing establishment and spread Invasion process The ability for Hydrilla to adapt to a wide range of conditions and easily reproduce Pathways, vectors and routes of introduction new plants from fragments of itself it is easily Hydrilla can use various vectors and pathways to spread when at new areas. Hydrilla can also travel from region to region and become easily spread through horticulture industry when introduced to new areas. Most common fragments of tubers are present in other plants. pathways within the United States are most Because it can grow in a wide range of likely through recreation. Boaters going from conditions it can be commonly found in areas of one lake to the next can easily can pick up the low nutrients and areas of high nutrients fragments or seeds of the plant and introduce it (Langeland 1996). to a new area. It was believed that hydrilla was first introduced into the United States through Potential ecological and/or economic impacts the aquarium trade in the late 1950’s (Madeira et Hydrilla poses a significant economic threat on a al. 200). region. Because it is a very difficult species to For the Pacific Northwest there are two control it can cost a region millions of dollars if hypotheses for how Hydrilla got into Pipe Lake established. It can grow to clog waterways, and and Lucerne Lake. Because the lakes are interfere with fishing, boating, and other secluded and don’t have boat docks it is not recreational activities. Lakeside property value believed that recreational boating is a vector to can also decrease with the presence of hydrilla. the lakes. One of which is by the Aquarium If left untreated it would cost millions to repair trade (WA dept. of Eco.). It was believed that the damages made by hydrilla. Unfortunately, if someone might have dumped their aquarium out established, there is a significant cost to manage into the lake. There have been reports of people it. Florida can range from 18-30 million dollars owning hydrilla in there aquariums due to being annual just to manage the plant (WA dept. of eco.). According to the Washington State’s In 1995 King County began applying Hydrilla Eradication project annual reports, to both Pipe Lake and Lake Lucerne. They used King County has spent over half a million herbicide with the active ingredient of fluridone dollars eradicating hydrilla from Pipe Lake and (WA Dept. of Eco). They applied the herbicide Lake Lucerne. for over eight weeks during the summer months Because Hydrilla grows to create large mats on at levels between 10 and 20 ppb. They repeated the surface water it can shade out other aquatic this process until the year 2000 where they plants and significantly decline the native plant stopped due to the National Pollution Discharge diversity and abundance (langeland 1996). It Elimination System (NPDES) permitting can also change the food web by decreasing the requirements for treatments with number of larger fish that won’t have the (WA Dept. of Eco). In 2001 SCUBA divers feeding habitat. It can also lower dissolved began to hand pull the hydrilla out of the lakes oxygen levels which can stress fish. and was the only method of control until 2003. Ecologically, hydrilla dominates the ecosystem In 2003 herbicides were again used after making it more difficult for the native species to surveying the lakes and observing hydrilla survive. growth. Since 2003 herbicide and divers have been the only treatment methods for hydrilla. Management strategies and control methods The lakes are under monitoring now with signs showing that eradication is near (Katie Messick). Hydrilla is currently classified as a federal noxious weed in the United States. Extensive research has been done to find the most successful means of control and eradication for hydrilla. Several methods and combinations of methods have been proven to be successful. Herbicide is one of the most common methods with various types, using different active ingredients. Bio control has been an affective type of control but it does not have the capability of eradicating hydrilla from any given location (Balciunas and Minno). So far the best method has been a combination of herbicides and mechanically removing the plants (WA dept. of Eco.).

Figure 5: Pipe Lake and Lake Lucerne in 1995 still heavily infested with Hydrilla (top). Pipe Lake and Lake Lucerne in 2002 after several years of management control with significant results (bottom). (WA Dept. of Eco.) Literature cited Madeira, P.T., Jacono, C.C., and Van, T.K. 2000. Monitoring hydrilla using RAPD Balciunas, J.K. and Minno, M.C., 1985 Insects procedures and the nonindigenous aquatic damaging Hydrilla in the USA. J. Aquat. species database. J. Aquat. Plant Manage. Plant Manage. 23: 77-83 38: 33-40

Barko, J.W., Smart, R.M., McFarland, D.G. and Steward, K.K., and Van, T.K., 1987. Chen, R.L., 1988. Interrelationships Comparative studies of Monoecious and between the growth of Hydrilla verticillata dioecious Hydrilla (Hydrilla verticillata) (L.f.) Royle and sediment nutrient biotypes. Weed Sci. 35: 204-210 availability. Aquat. Bot., 32: 205-216. Sutton D.L., Van, T.K., and Portier, K.M. 1992. Blackburn, R.D., and Weldon, L.W., 1969. Growth of dioecious and monoecious Control of Hydrilla verticillata. Proc. So. hydrilla from single tubers. J. Aquat. Plant Weed Conf. 22:317 Manage. 30: 15-20

Boersma, P.D., Reichard, S.H., and Van Buren, Other key sources of information and A.N. (Eds.). Invasive Species in the Pacific bibliographies Northwest. Seattle, Wa: University of Washington Press, 2006. 285pp. ISBN 0- Columbia University. Invasion biology of 295-98596-8 hydrilla http://www.columbia.edu/itc/cerc/danoff- Langeland, K.A. 1996. Hydrilla verticillata burg/invasion_bio/inv_spp_summ/Hydrilla_verti (L.F.) Royle (Hydrocharitaceae), "The cillata.html#Identification Perfect Aquatic Weed". Castanea 61:293-

304 Indiana Department of Natural Resources.

Aquatic Invasive Species Madeira, P.T., Coetzee, J.A., Center, T.D., http://www.in.gov/dnr/files/hydrilla.pdf White, E.E. and Tipping, P.W., 2007. The

origin of Hydrilla verticillata recently Massachusetts Department of Conservation and discovered at a South African dam. Aquat. Recreation. Rapid response plan for Bot., 87: 176-180 Hydrilla

http://www.mass.gov/dcr/watersupply/lakepond/ downloads/rrp/hydrilla.pdf

Menninger, Holly. Hydrilla verticillata in the Cayuga Inlet: NY Invasive Species Research Institute http://www.nyis.info/user_uploads/files/NYISRI %20Hydrilla%20%20Briefing_Outreach.pdf

Washington State Department of Ecology http://www.ecy.wa.gov/programs/wq/plants/wee ds/aqua001.html

Expert contact information in PNW Katie Messick Aquatic Weed Specialist King County Noxious Weed Control Program Phone: (206) 263-6461 [email protected]

Current research and management efforts There is still research being done on the best way to control hydrilla infestations around the United States. As of 2007 Washington has not seen hydrilla in the lakes. The lakes are under observation for the next five years to see if hydrilla sprouts again. Divers are still currently checking the lake floor to find any remnants but as of now herbicide is not being injected into the water (Kate Messick).