Recipient ecosystem productivity influences effects of resource pulses in mesocosms

Abstract

Resource pulses are found in a variety of ecosystems and are becoming a prevailing theme in ecology. However, limited information is available regarding how recipient ecosystem productivity influences effects of resource pulses. Our objective was to compare the abundance, stability, and food web responses of nutrients and primary producers and consumers in oligotrophic versus eutrophic aquatic mesocosms receiving resource pulses of decaying fish. Nutrient availability and primary producer and consumer abundance were generally different between trophic states and pulsed treatments. Nitrate decreased and phytoplankton increased as a result of the pulse, whereas total Kjeldahl nitrogen, copepods, and total zooplankton increased following the pulse in oligotrophic but not eutrophic mesocosms. Gastropod density was higher in non-pulsed oligotrophic compared to pulsed eutrophic mesocosms but was not affected by the pulse within a trophic state. Despite temporal variation of all parameters, ecosystem stability was not affected by the pulse. Several differences in δ15N and δ13C values were also observed between biota in oligotrophic and eutrophic mesocosms, but only amphipod δ13C values in eutrophic mesocosms were depleted by the pulse. Overall, our results indicate that recipient ecosystem productivity is an important factor regulating the effects of resource pulses, with implications for ecosystems and food web structure.