Can adult Ephemeroptera replace nymphs in stream bioassessment? A taxonomic congruence approach in neotropical streams

Abstract Monitoring tropical streams uses benthic macroinvertebrates; however, identification constraints and long processing times limit its application. Taxonomic surrogacy has been proposed, but its ecological validity is uncertain. Ephemeroptera are used as bioindicators because their nymphs are highly sensitive to environmental change. However, nymph identification is often limited by fragile structures, whereas adults retain stable traits, and it remains unclear whether imagos can act as surrogates without ecological information loss. Therefore, we evaluated congruence within and between life stages across protected areas and their relationships with environmental variables to assess whether one stage can substitute the other in biomonitoring. We sampled 40 Atlantic Forest streams across two distinct geographic regions, collecting nymphs with D-net and adults with Malaise and Pennsylvania traps. Specimens were identified to the genus level. We evaluated community structure using richness, abundance, and occurrence and tested congruence between life stages and assemblages metrics using Procrustes analysis. We collected 3067 individuals, 1882 nymphs and 1185 adults. Leptophlebiidae and Leptohyphidae were the dominant families for nymphs and adults, respectively. Relations with environmental variables was weak and stage dependent. Abundance and occurrence data were highly congruent within life stages (96–97%). However, cross-stage congruence was low and nonsignificant, suggesting distinct ecological filters between stages, for example, benthic microhabitat for nymphs versus dispersal and phenology for adults, limiting cross-stage surrogacy. Within stages, abundance and occurrence metrics were interchangeable, but adults cannot replace nymph assemblages. Therefore, integrated approaches that combine multiple metrics and life stages enhance the precision and effectiveness of biomonitoring studies.