We conducted preliminary investigations into some of the potential effects of Australian swamp stonecrop, a nonnative invasive aquatic plant in the U.K., on native pond plants and newt populations. Four studies were carried out in the northwest of England, in the field and under controlled conditions, during the period 2002 to 2003. Six plant species, which are important to newts as an egg-laying substrate, showed significant germination suppression up to 83% under Australian swamp stonecrop. However, there was no significant effect of Australian swamp stonecrop on pond seed banks, and no significant loss of plant species was observed in ponds invaded by the weed. Smooth newt eggs hatched at a later developmental stage when laid on Australian swamp stonecrop compared with those laid on the native substrate watercress, generally considered to be a preferred species. No significant differences in developmental stage at hatching could be detected between substrates in the great crested newt, a protected species.

Nomenclature: Australian swamp stonecrop or New Zealand pigmyweed, Crassula helmsii (Kirk) Cockayne; watercress, Rorippa nasturtium-aquaticum (L.) Hayek; great crested newt, Triturus cristatus (Laurenti, 1768); smooth newt, Triturus vulgaris (Linnaeus, 1758).

Additional index words: Aquatic plants, invasive, nonnative, species interactions, urodele amphibians.