Ceratophyllum demersum
(coontail)

C. demersum is a cosmopolitan submerged aquatic species that has probably already invaded most of its potential exotic range. It has the advantages of being a perennial surviving well overwinter in deeper water and by growing both by asexual reproduction of broken or complete stems and by sexual reproduction of very many seeds. It has a wide ecological tolerance and grows relatively fast. Disturbance of the water body results in increases in growth through changes in nutrient availability but also in faster dispersal around water bodies allowing greater competition with less vigorous species.

C. demersum is a rootless aquatic macrophyte with a cosmopolitan distribution; it has a wide ecological tolerance. When water is disturbed, it is quite common for native species to increase their growth and become a threat to human use of the water body. Frequently, disturbance of the bed of the water body or soils in the catchment results from an increase in the trophic level of the water or the substrate. C. demersum has become locally troublesome on several occasions (Cook, 1990). It is one of the 26 aquatic vascular plant species that Cook (1985) characterized as 'very widespread', and is unlikely to be native throughout its whole range of occurrence.

In general, C. demersum occurs in quiet or slow flowing, hard calcareous, nutrient-rich or eutrophic waters of streams, ditches ,canals, ponds and lakes as a near free-floating aquatic plant where it may form large masses. It is especially favoured by nitrate-rich conditions where it grows in greater abundance (Goulder and Boatman, 1971; Toetz, 1971; Best, 1980; Kulshreshta, 1982). It is a cosmopolitan species. Although the plant is considered rootless, it bears some appendages which assist in delaying movement around the shallower margins of lakes under the influence of, for example, wind fetch.

C. demersum is a perennial, submerged aquatic angiosperm, branching but with a single branch produced per node. Roots are lacking, but leafy branches are sometimes modified as rhizoids; stems break easily and the pieces continue growth separately (Godfrey and Wooten, 1981).

In temperate regions, C. demersum plants perennate by dormant apices on the lake bottom, where these organs are covered by a layer of detritus. Dormancy is initiated in late summer and autumn when elongation growth of the lateral shoots ceases, and tightly clustered, dark-green leaves, which contain high levels of starch, are formed. The dormant apices remain attached throughout winter or become liberated, depending on the disintegration rate of the parent axis. In temperate regions, liberation of the hibernacula [winter buds] is an important means of dispersal, because water temperatures are too low for flowering and seed development. In late spring the axis elongates, the leaves expand and a new plant starts to grow.

During growth the plants tend to concentrate most of their biomass in the upper half of their height and often reach the water surface. At the end of the growth season, the plants senesce rapidly and, in doing so, lose substantial amounts of nutrients (Pomogyi et al., 1984). Decomposition of the plant material proceeds rapidly: most of the dead plant biomass decomposes and disintegrates  before the next growth season starts, leaving only and a small fraction of organic matterial in the water body (Best et al., 1990). Phenological cycle, growth and primary production have been described (Sculthorpe, 1971; Best and Dassen, 1987 [and citations therein]). Photosynthesis has been investigated intensively (Carr, 1969; Van et al., 1976; Best and Meulemans, 1979; Fair and Meeke, 1983; Sand-Jensen and Madsen, 1991). A simulation model to calculate biomass formation has been developed by Best and Jacobs (1990).

Flowering does occur in warmer areas: for example, seeds were abundant in Papua New Guinea (Osborne and Polunin, 1986). Pollen transport is hydrophilous [via water]: recent studies indicate that, at the population level, hydrophilous taxa have a lower percentage of polymorphic loci, fewer alleles per locus, and lower levels of heterozygosity than non-hydrophilous plants. These patterns may be explained by limited sexuality, extensive vegetative spread and the greater isolation of freshwater populations (lakes may be considered as 'islands') relative to most terrestrial plant species and to coastal species such as Zostera marina (Les, 1991; Barrett et al., 1993; Laushman, 1993).

Triploid grass carp (Ctenopharyngodon idella) were successfully used to control water weeds including C. demersum, in waterlily production ponds in Brookshire, and in Lake Conroe, both in Texas, USA (Martyn et al., 1986; Santha et al., 1994), in Iowa, USA (Mitzner, 1976), and in Thailand (Pholprasith et al., 1978). Grass carp also proved useful in tropical areas, such as Egypt (Khattab and El-Gharably, 1986).

The larvae of Parapoynx diminutalis, an Asian pyralid moth adventive on Hydrilla verticillata, were able to remove considerable C. demersum biomass (Buckingham and Bennett, 1989). The nematode Hirschmanniella caudacrena may be pathogenic to C. demersum (Gerber et al., 1986; Gerber and Smart, 1987).

Several fungi have been tested to control aquatic weeds. Mycoleptodiscus terrestris, a microbial herbicide candidate for Myriophyllum spicatum, also proved pathogenic to C. demersum when applied as alginate beads (Verma and Charudattan, 1993).

Animal feed, fodder, forage

• Fodder/animal feed

Environmental

• Wildlife habitat

General

• Ornamental
• Pet/aquarium trade

Materials

• Manure
• Mulches

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

Netherlands: European Weed Research Society - EWRS, Postbus 29, NL-6865 ZG Doorwerth, http://www.ewrs.org

UK: Centre for Ecology and Hydrology - CEH, CEH Wallingford, Maclean Building, Crowmarsh Gifford, Walingford, Oxfordshire, http://www.ceh.ac.uk/

UK: Environment Agency, National Customer Contact Centre PO Box 544, Rotherham S60 1BY, http://www.environment-agency.gov.uk/

14/01/2008 Updated by:

Hugh Dawson, CEH Wallingford, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB, UK