Survival and biomass of exotic earthworms, Aporrectodea spp. (Lumbricidae), when introduced to pastures in south-eastern Australia

Abstract

The earthworm fauna of pastures in south-eastern Australia is dominated by exotic lumbricid earthworms, in particular the endogeic species, Aporrectodea caliginosa and A. trapezoides. Anecic species such as A. longa are very rare. All 3 species were introduced within cages in 10 pastures on a range of soil types within the region. Five months later, A. longa had generally survived the best and A. trapezoides the worst. The survivals and weights of individual worms varied between sites for all 3 species. The survivals of A. caliginosa and A. longa, and to a lesser extent A. trapezoides, were positively correlated with soil clay content. The weights of A. caliginosa and A. longa, but not A. trapezoides, were positively correlated with soil P content. The survivals and weights of A. longa and A. trapezoides and the weights only of A. caliginosa decreased with increasing inoculation density, suggesting increased intraspecific competition for resources, particularly in the first two species. A. longa reduced the abundance and biomass of the exotic acanthodrilid earthworm, Microscolex dubius, at one site, and the total biomass of 3 native megascolecid species at another, when these latter species occurred as contaminants in A. longa cages. The addition of lime had no effect on the survivals and weights of A. caliginosa, A. longa, and A. trapezoides, although the soils were acid at the sites tested. The addition of sheep dung increased the survival and weights of some species at some sites. Mechanical disturbance of the soil within cages reduced the survivals of A. longa and A. trapezoides. A. longa was released without being caged at 25 sites within one pasture in South Australia. Four years later, it was recovered at all release points. A. longa has the potential to colonise pastures widely throughout the higher rainfall regions of south-eastern Australia.