Resilience to changes in lake trophic state: Nutrient allocation into resting eggs.

During past decades, many lakes underwent drastic human-caused changes in trophic state with strong implications for population dynamics and food web processes. We investigated the influence of trophic state on nutrient allocation into resting eggs. The production of resting eggs is an important survival strategy, allowing to cope with unfavorable environmental conditions. Allocation of essential nutrients into resting eggs may crucially influence embryonic development and offspring survival and thus is of great ecological and evolutionary interest. The capacity of to adjust the allocation of nutrients into resting eggs may depend on the dietary nutrient supply, which may vary with trophic state-related changes in the phytoplankton community composition. Resting eggs were isolated from sediment cores taken from Lake Constance, a large prealpine lake with a distinct eutrophication and reoligotrophication history, and analyzed for elemental (carbon, nitrogen, and phosphorus) and biochemical (sterols and fatty acids) nutrients. Carbon allocation into resting eggs continuously decreased over time, irrespective of changes in trophic state. The allocation of nitrogen into resting eggs followed the changes in trophic state, that is, nitrogen concentrations in resting eggs increased with eutrophication and decreased again with reoligotrophication. The allocation of phosphorus, sterols and long-chain polyunsaturated fatty acids, such as eicosapentaenoic acid, into resting eggs did not change significantly over time. Changes in trophic state strikingly influenced all trophic levels in Lake Constance. However, nutrient allocation into resting eggs was mostly resilient to changes in lake trophic state.