Resource depletion affects the structure of an experimental benthic food web

In this study, we investigated the long-term (2-year) response of a detritus-based food web to resource depletion simulated in microcosms filled with lake sediment. The effects of resource depletion on the food web were estimated from the biomass responses of a simplified, size-based trophic network comprising three trophic levels: (1) bacteria, (2) bacterivorous meiofauna, and (3) omnivore/predacious nematodes and oligochaetes. The results showed that sediment bacteria and organic carbon stock were not affected by resource depletion, whereas oligochaetes, large nematodes and some bacterivores, such as rotifers and ostracods, decreased dramatically. At the same time, resource depletion had no negative effect on minute bacterivorous nematodes and harpacticoid copepods, suggesting their release from competition with other bacterivores and/or their release from potential predation by large nematodes and oligochaetes. Our results globally confirmed classical trophic dynamics models in which a shortage in resources dampens food-chain length. Yet, low resources did not completely eliminate all large invertebrates, and did not affect the standing stock of detritus and bacteria, suggesting that detritus-based food webs could show a remarkable resilience to the effects of resource depletion.