Ecological Memory of Historical Contamination Influences the Response of Phytoplankton Communities

Abstract Ecological memory (EM) recognizes the importance of previous stress encounters in promoting community tolerance and thereby enhances ecosystem stability, provided that gained tolerances are preserved during non-stress periods. Drawing from this concept, we hypothesized recruitment tolerant species can be facilitated by imposing an initial sorting process (conditioning) early stages assembly, which should result higher production (biomass development photosynthetic efficiency) stable composition. To test this, phytoplankton resting were germinated lake sediments originating two catchments differed contamination history: one impacted long-term herbicides pesticides exposures (historically contaminated lake) agricultural catchment compared to a low-impacted (near-pristine forested catchment. Conditioning was achieved adding herbicide (Isoproturon, commonly used historically germination. Afterward, communities obtained germination exposed increasing gradient Isoproturon. As hypothesized, upon conditioning, assemblages able rapidly restore efficiency ( p > 0.01) became structurally (community composition) more resistant The near-pristine did not yield these positive effects regardless supporting EM unique attribute stressed ecosystem. Moreover, displayed structural resistance concurrently yielded lower biomass, indicating benefits stability may trade-off with production. Our results clearly indicate foster recurring stressor.