The distribution and abundance of the submerged water-weed, Lagarosiphon major in Lake Taupo / by Clive Howard-Williams, John Davies and Virginia Reid.

"This report is provisional and should not be quoted without consulting the author or Director"

Lagarosiphon major is the most conspicuous and most important weed species in Lake Taupo. This study documents the distribution pattern of the species and its abundance and rates of growth in the lake. Horizontal distribution around the lake is patchy and long stretches of coast have no weed problems. Nuisance growths of #L. major# occur on 10% of the coast. The plant occurs to a maximum depth of 6.5 m., and in areas where it grows in abundance it had caused a major loss to the native aquatic vegetation. These areas are largely demarcated by exposure to wave action. An inverse relationship between exposure and the height and biomass of the weed beds is demonstrated. Weed bed growth rates were not rapid, being always less than 2% per day, and at any one site there was considerable temporal variability in growth. Weed beds grew upwards, collapsed and regrew in a cyclical pattern. Management issues of this and other aquatic weeds in Lake Taupo are discussed in relation to weed control in boat ramp and swimming areas, control of "duck itch" and conservation of the native flora. Information gaps are identified. (auths)