An assessment of aquatic amphibian biodiversity on the California Lost Coast

Abstract

One of the most difficult aspects of studying intact amphibian communities is that they tend to occupy isolated areas within inaccessible terrain—factors that both protect watersheds from development and disturbance while also making them difficult to study. We conducted an extensive survey of the freshwater herpetofauna of the remote King Range National Conservation Area in Northern California using a combination of visual encounter surveys and environmental DNA (eDNA) sampling. We found twelve species of native aquatic amphibians and the western pond turtle (Actinemys marmorata), and no introduced amphibians. Detection probabilities for the four most commonly encountered species, giant salamanders (Dicamptodon sp), foothill yellow-legged frogs (Rana boylii), western toads (Anaxyrus boreas), and black salamanders (Aneides flavipunctatus), were affected by substrate and canopy cover, but the effects of these habitat characteristics on detection probability were species specific. Neither survey method, visual encounter surveys nor eDNA sampling, was more effective than the other, and our study suggests that the use of visual encounter surveys in conjunction with eDNA sampling may counteract the shortcomings of either when done individually. Five species were found using both methods, seven were only encountered during visual encounter surveys, and one recorded only from eDNA sampling. DNA samples from two taxa, toads and giant salamanders, could not be resolved to species. Toad species identity was assigned to the only member of the candidate species with a species range known to overlap the study area; the other three candidate species occupy restricted ranges far from the study area. Neither of the two giant salamander candidate species have known species ranges overlapping the study area. One, the California giant salamander (D. ensata), is known to occur within 100 km. However, there is a paucity of genetic material in GenBank DNA library for both the California giant salamander and the coastal giant salamander (D. tenebrosus), a widely distributed species with a range overlapping the study area, which could lead to inaccurate assignment of eDNA fragments.