Morphology and dynamics of calcium carbonate granules produced by different earthworm species

Granules of calcium carbonate produced by earthworms are regularly found in soil profiles, but little is known of their origins and dynamics. Pure cultures of a range of species were therefore set up, using artificial soils, and the granules recovered for examination. Species of Lumbricus, Aporrectodea, Octolasion and Allolobophora all produced granules larger than 0.125 mm, but Eisenia hortensis did not. For comparison, two compost-dwelling Eisenia species were also cultured. These yielded no granules at all, suggesting that the genus as a whole does not produce granules, consistent with its lack of calciferous sacs. Granules recovered from the other 7 species have a variety of sizes and morphologies, ranging from single calcite crystals to aggregations up to 2.5 mm in diameter. SEM photographs of the granules and data on granule concentrations in relation to depth are presented.