New Zealand Journal of Marine and Freshwater Research abstracts

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Effects of fluctuations in water level and growth of Lagarosiphon major on the aquatic vascular plants in Lake Rotoma, 1973-80

J. S. CLAYTON

Botany Department University of Auckland Private Bag Auckland, New Zealand

Abstract Fluctuations in water level and the growth of the introduced exotic Lagarosiphon major (Ridley) Moss have significantly influenced the submerged vegetation of Lake Rotoma over the period 1973-80. Low lake levels temporarily reduced the proportion of native vascular plants by removing available shallow-water habitats through erosion, siltation, or desiccation. High lake levels have allowed native vascular plants to re-establish from seed and rhizomes. Fluctuations in water level appear to have reduced the long-term replacement of native species by L. major, which has none the less spread progressively around the lake. Water-level fluctuations enhanced its rate of fragmentation, and thus its dispersal and establishment. The annual increase in the proportion of L. major has been primarily at the expense of the shallow-water characean algae, but also partly by competitive displacement of native vascular plants. The southwest inlet of Lake Rotoma had an exceptionally high plant density, with up to 3518 g/m² dry weight of L. major (believed to be a world record for submerged plant biomass); this is attributed to local enrichment and protection from wave exposure.

Keywords Lake Rotoma; water level fluctuations; aquatic plants; biological surveys; Lagarosiphon major, Hydrocharytaceae; biomass; Elodea canadensis; freshwater weeds; freshwater lakes. Received 8 January 1981; revised 31 July 1981 Bag, Hamilton, New Zealand

New Zealand Journal of Marine and Freshwater Research, 1982, Vol. 16 : 89-94Received 8 January 1981; revised 31 July 1981

PDF file of entire paper: medium quality (486K); (scanned from paper original: notes about this process)

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