Juvenile drift of an invasive crayfish Faxonius virilis (Hagen, 1870) (Decapoda: Astacidea: Cambaridae) in the middle Pecos River, New Mexico, USA

Abstract

Abstract Ecologists have long recognized that dispersal capabilities influence range expansion by nonnative species. Some of the most disruptive crayfish invaders are highly mobile as adults within and across watershed networks. In this study, we contribute a new facet to our understanding of crayfish early life history and invasions by documenting strong evidence of synchronized, behavioral downstream drift by early juveniles. During 2019, we observed a relatively dense springtime pulse of juvenile crayfish in drift nets set at two sites in the middle Pecos River near Fort Sumner, New Mexico. To determine whether this was an anomalous episode or an annual event, we sampled in 2020 and 2021 to: 1) determine the timing and extent of drifting behavior relative to environmental variation, and 2) identify the drifters to species level using DNA barcoding. Across three years, we collected juvenile crayfish (2.4–13.1 mm carapace length) after sunset during April through June in relatively clear water conditions (5–64 NTU) that coincided with minimum flows (41–152 cfs) and seasonally typical temperatures for this region (15–26 °C). To identify specimens to species level, we sequenced the barcoding region of the cytochrome c oxidase I (COI) DNA barcode for 35 juveniles and 6 adult male vouchers that represented all years. Based on morphological identifications of adult males and COI sequence comparisons to published reference specimens, nearly all drifting juveniles were identified as Virile Crayfish Faxonius virilis (Hagen, 1870). Drifters matched the sizes of second-molt juveniles newly released in the laboratory from two brooding females that we captured in the field. Faxonius virilis has been collected throughout the Rio Grande watershed, but not yet been reported in the Pecos River. As drifting early life stages are common across crustaceans, we suspect juvenile crayfish drift is probably not unique to F. virilis nor to our study system. We encourage others to perform targeted surveys of juvenile drift across a broad range of study systems, and to identify causal factors and ecological consequences of juvenile drift using controlled experiments.