Extraordinarily high earthworm abundance in deposits of marine macrodetritus along two semi-arid beaches

• Published in: Marine ecology. Progress series (Halstenbek) 2008-06, Vol.361, p.181-189
• Main Authors: Coupland, Grey T., McDonald, Justin I.
• Format: Article
• Language: English
• Subjects: Aquatic habitats; Beaches; Earthworms; Forest habitats; Forest soils; Habitats; Isotopes; Macroalgae; Marine; Pontodrilus; Soil ecology; Worms
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps07351

Earthworms are common in most soil profiles; however, the abundance of earthworms varies greatly among habitats. The euryhaline earthwormPontodrilus litoraliswas 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–2at one site. Mean (±SE) worm density was 3200 ± 466 m–2for the north Leeman site, with a minimum density of 750 m–2at 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–2yr–1of wrack material deposited at Point Louise and 31 kg m–2yr–1at 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.