Free-living terrestrial nematodes indicate decomposition pathways of aquatic insect subsidies

Insects can connect aquatic food webs to the surrounding terrestrial environment. At Lake Mývatn in northeast Iceland billions of midges (Chironomidae) emerge from the lake, swarm over the shore to mate, and die. Their carcasses then become available to detritivores such as collembola, mites, and nematodes. The latter of these are indicators of bottom-up changes to soil food webs. Nematodes play an important role in soil food webs by consuming bacteria, fungi, and plants, and contributing to the mineralization of nitrogen, while also being consumed by various arthropods. As fungal and bacterial decomposers increase in abundance with midge inputs, the proportion of fungal and bacterial feeding nematodes are expected to increase. We studied the effect of midge deposition on soil food webs around lakes in the Lake Mývatn region during the summer of 2010. Soil nematodes were extracted from long-term research plots that have received midge additions for three years, short term plots with only recent midge additions, and along a natural midge deposition gradient at varying distances from the lake margin. Nematodes were classified based on the maturity index using colonizer-persister functional guilds. Midge inputs increased the proportion of early colonizer-persister nematodes within the nematode assemblage. The response of free-living terrestrial nematodes to midge input allows us to better understand decomposition pathways by which midges enter terrestrial ecosystems.