Community and ecosystem response to a pesticide disturbance in ponds: The role of assembly history and compositional variability

Background/Question/Methods Agricultural practices, including the use of pesticides, pose a major threat to the biodiversity and integrity of freshwater systems. Previous research has shown that the application of pesticides can have strong negative consequences for aquatic communities. However, little is known about community recovery from this anthropogenic disturbance. To investigate community recovery, the pesticide Sevin® (active ingredient carbaryl) was added to aquatic mesocosms with different assembly histories. Mesocosms were located near one of two source ponds and macroinvertebrate communities were either: 1) created via natural colonization events or 2) hand-assembled through manual addition of organisms, thereby incorporating community compositional variability. The impact of carbaryl on these communities and the degree of recovery by the different assemblages was investigated through comparisons to control mesocosms. Results/Conclusions Community and ecosystem responses to the addition of carbaryl were similar across mesocosms with different assembly histories. Disturbed mesocosms experienced a loss in species richness and abundance for both zooplankton and macroinvertebrate communities. Following the degradation of carbaryl, aggregate community response variables recovered to pre-disturbance and control levels, although differences in community composition remained between disturbed and control mesocosms. Despite differences in assembly histories and initial community composition, communities responded similarly to a pesticide disturbance. However, disturbed communities did not return to their initial states, which warrants future research into the mechanisms and processes responsible for community recovery.