MEPS prepress abstract  -  doi: 10.3354/meps07351

ABSTRACT: Earthworms are common in most soil profiles, however, the abundance of earthworms varies greatly among habitats. The euryhaline earthworm Pontodrilus litoralis was recorded in extraordinarily high numbers in wrack material deposited on arid beaches along the western Australian coastline. Based on worm abundance in 20 cm x 20 cm x 20 cm plots, we estimated worm densities to be as high as 4,875 m^-2 at one site. Mean worm density was 3,200 m^-2 (± 466 SE) for north Leeman site, with a minimum density of 750 m^-2 at the Point Louise site (mean 1,940 m^-2 ± 475 SE). Using estimates of consumption by earthworms from previous research, we calculated earthworms could consume approximately 19 kg m^-2 year^-1 of wrack material deposited at Point Louise and 31 kg m^-2 year^-1 at the north Leeman site. The densities and associated potential consumption rates of worms recorded in the wrack habitat well exceeds any records made of worm populations in other natural systems. The only similar estimates are those from artificially created habitats, such as manure heaps. Stable isotope analyses suggest that the earthworms (mean δ¹⁵C -15.9 and δ¹⁵N 6.9) were consuming the more ephemeral algal component (mean δ¹³C -21.5 and δ¹⁵N 3.7) of the wrack in preference to the more persistent seagrass material (mean δ¹³C -12.4 and δ¹⁵N 2.1). The extraordinary densities of earthworms in wrack habitat have implications for the rate of wrack turnover along beach habitats and incorporation marine derived nutrients into what is essentially a nutrient poor terrestrial coastal system. High earthworm densities in the wrack also indicates that wrack as a habitat is a potential hotspot for diversity and metabolism, likely exceeding records for other more stereotypically rich habitats, such as rainforests.