Why didn’t the nudibranch cross the ocean? Understanding biogeographic and evolutionary relationships ofHermissenda(Nudibranchia: Myrrhinidae) Bergh, 1878

Abstract

AbstractIn the aftermath of the 2011 east Japanese earthquake and tsunami, anthropogenic debris from the east coast of Japan floated across the Pacific Ocean to the west coast of North America. One such vessel from Iwate Prefecture arrived on the coast of Oregon, and the fouling community included specimens identified as the nudibranchHermissenda crassicornis, which was previously thought to range from Japan to Baja California but has since been split into three species:H. crassicornis(Alaska to southern CA),H. opalescens(British Columbia to Baja California), andH. emurai(Japan, Korea, Russian Far East). Previous work suggested that all of the motile invertebrates found in the tsunami debris fouling community were either pelagic or Japanese in origin. Our study sought to determine whether the nudibranch specimens collected from the Iwate vessel were, according to the new classification system, onlyH. emuraior whether the Eastern PacificHermissendawere present as well. Results from DNA sequencing and morphological analysis suggest that specimens ofH. crassicornis, as it is currently recognized, andH. opalescenswere found on the vessel.This finding indicates either that these species settled after arrival to the west coast of North America or thatH. crassicornisandH. opalescensis found in Japan, suggestingHermissendaranges need to be investigated further.Occurrence data shared on the iNaturalist platform were also used to assess current ranges. Our phylogenetic tree and haplotype network constructed from COI data from allHermissendaspecies indicate thatH. opalescensandH. emuraiare most closely related withH. opalescenssister to the clade that containsH. opalescensandH. emurai. This study demonstrates the power of combining volunteer naturalist data with lab-collected data to understand evolutionary relationships, species ranges, and biogeography.