MACROINVERTEBRATES AND LITTER NUTRIENT RELEASE ON A SUB-ANTARCTIC ISLAND

For most plant communities on Marion Island (47-degrees-S, 38-degrees-E), mineralization of the large reserves of organic matter is the main process supplying nutrients for plant growth. However, due to the constantly low temperature, soil acidity and waterlogging, rates of nutrient release mediated by microorganisms alone are too low to account for the amounts taken up by the vegetation. Microcosm studies showed that the rate of inorganic nutrient release from plant litter is generally enhanced by moth larvae, earthworms, weevil larvae and adults, snails and slugs. Overall, moth larvae and slugs exerted the greatest influence across all nutrients tested (nitrogen, phosphorus, calcium, potassium, magnesium and sodium), although the effect was most consistently significant for nitrogen and phosphorus. The influence of the other invertebrate species was mostly limited to particular animal/nutrient combinations, which were fairly consistent across litter types, e.g. earthworms for nitrogen and phosphorus, snails for calcium and weevil adults for potassium. These findings suggest that, by 'short-circuiting' the slow microbially mediated mineralization of nutrients from organic matter, soil invertebrates are important agents of nutrient cycling on the island.