MEPS 361:181-189 (2008)  -  DOI: https://doi.org/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 × 20 × 20 cm plots, we estimated worm densities to be as high as 4875 m^–2 at one site. Mean (±SE) worm density was 3200 ± 466 m^–2 for the north Leeman site, with a minimum density of 750 m^–2 at the Point Louise site (1940 ± 475 m^–2). Using estimates of consumption by earthworms from previous research, we calculated that earthworms could consume approximately 19 kg m^–2 yr^–1 of wrack material deposited at Point Louise and 31 kg m^–2 yr^–1 at north Leeman. The densities and associated potential consumption rates of worms recorded in the wrack habitat well exceed any records 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 δ¹³C –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 of marine-derived nutrients into what is essentially a nutrient-poor terrestrial coastal system. High earthworm densities in the wrack also indicate that wrack as a habitat is a potential hotspot for diversity and metabolism, probably exceeding records for other more stereotypically rich habitats, such as rainforests.

KEY WORDS: Coastal systems · Detached macrophytes · Land–water interface · Nutrient turnover · Wrack